Fix inconsistencies in the code

[postgresql] / src / backend / catalog / namespace.c

/*-------------------------------------------------------------------------
 *
 * namespace.c
 *        code to support accessing and searching namespaces
 *
 * This is separate from pg_namespace.c, which contains the routines that
 * directly manipulate the pg_namespace system catalog.  This module
 * provides routines associated with defining a "namespace search path"
 * and implementing search-path-controlled searches.
 *
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        src/backend/catalog/namespace.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/parallel.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "catalog/dependency.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_conversion.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_statistic_ext.h"
#include "catalog/pg_ts_config.h"
#include "catalog/pg_ts_dict.h"
#include "catalog/pg_ts_parser.h"
#include "catalog/pg_ts_template.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#include "funcapi.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "parser/parse_func.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/sinvaladt.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/catcache.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
#include "utils/varlena.h"


/*
 * The namespace search path is a possibly-empty list of namespace OIDs.
 * In addition to the explicit list, implicitly-searched namespaces
 * may be included:
 *
 * 1. If a TEMP table namespace has been initialized in this session, it
 * is implicitly searched first.  (The only time this doesn't happen is
 * when we are obeying an override search path spec that says not to use the
 * temp namespace, or the temp namespace is included in the explicit list.)
 *
 * 2. The system catalog namespace is always searched.  If the system
 * namespace is present in the explicit path then it will be searched in
 * the specified order; otherwise it will be searched after TEMP tables and
 * *before* the explicit list.  (It might seem that the system namespace
 * should be implicitly last, but this behavior appears to be required by
 * SQL99.  Also, this provides a way to search the system namespace first
 * without thereby making it the default creation target namespace.)
 *
 * For security reasons, searches using the search path will ignore the temp
 * namespace when searching for any object type other than relations and
 * types.  (We must allow types since temp tables have rowtypes.)
 *
 * The default creation target namespace is always the first element of the
 * explicit list.  If the explicit list is empty, there is no default target.
 *
 * The textual specification of search_path can include "$user" to refer to
 * the namespace named the same as the current user, if any.  (This is just
 * ignored if there is no such namespace.)      Also, it can include "pg_temp"
 * to refer to the current backend's temp namespace.  This is usually also
 * ignorable if the temp namespace hasn't been set up, but there's a special
 * case: if "pg_temp" appears first then it should be the default creation
 * target.  We kluge this case a little bit so that the temp namespace isn't
 * set up until the first attempt to create something in it.  (The reason for
 * klugery is that we can't create the temp namespace outside a transaction,
 * but initial GUC processing of search_path happens outside a transaction.)
 * activeTempCreationPending is true if "pg_temp" appears first in the string
 * but is not reflected in activeCreationNamespace because the namespace isn't
 * set up yet.
 *
 * In bootstrap mode, the search path is set equal to "pg_catalog", so that
 * the system namespace is the only one searched or inserted into.
 * initdb is also careful to set search_path to "pg_catalog" for its
 * post-bootstrap standalone backend runs.  Otherwise the default search
 * path is determined by GUC.  The factory default path contains the PUBLIC
 * namespace (if it exists), preceded by the user's personal namespace
 * (if one exists).
 *
 * We support a stack of "override" search path settings for use within
 * specific sections of backend code.  namespace_search_path is ignored
 * whenever the override stack is nonempty.  activeSearchPath is always
 * the actually active path; it points either to the search list of the
 * topmost stack entry, or to baseSearchPath which is the list derived
 * from namespace_search_path.
 *
 * If baseSearchPathValid is false, then baseSearchPath (and other
 * derived variables) need to be recomputed from namespace_search_path.
 * We mark it invalid upon an assignment to namespace_search_path or receipt
 * of a syscache invalidation event for pg_namespace.  The recomputation
 * is done during the next non-overridden lookup attempt.  Note that an
 * override spec is never subject to recomputation.
 *
 * Any namespaces mentioned in namespace_search_path that are not readable
 * by the current user ID are simply left out of baseSearchPath; so
 * we have to be willing to recompute the path when current userid changes.
 * namespaceUser is the userid the path has been computed for.
 *
 * Note: all data pointed to by these List variables is in TopMemoryContext.
 */

/* These variables define the actually active state: */

static List *activeSearchPath = NIL;

/* default place to create stuff; if InvalidOid, no default */
static Oid      activeCreationNamespace = InvalidOid;

/* if true, activeCreationNamespace is wrong, it should be temp namespace */
static bool activeTempCreationPending = false;

/* These variables are the values last derived from namespace_search_path: */

static List *baseSearchPath = NIL;

static Oid      baseCreationNamespace = InvalidOid;

static bool baseTempCreationPending = false;

static Oid      namespaceUser = InvalidOid;

/* The above four values are valid only if baseSearchPathValid */
static bool baseSearchPathValid = true;

/* Override requests are remembered in a stack of OverrideStackEntry structs */

typedef struct
{
        List       *searchPath;         /* the desired search path */
        Oid                     creationNamespace;      /* the desired creation namespace */
        int                     nestLevel;              /* subtransaction nesting level */
} OverrideStackEntry;

static List *overrideStack = NIL;

/*
 * myTempNamespace is InvalidOid until and unless a TEMP namespace is set up
 * in a particular backend session (this happens when a CREATE TEMP TABLE
 * command is first executed).  Thereafter it's the OID of the temp namespace.
 *
 * myTempToastNamespace is the OID of the namespace for my temp tables' toast
 * tables.  It is set when myTempNamespace is, and is InvalidOid before that.
 *
 * myTempNamespaceSubID shows whether we've created the TEMP namespace in the
 * current subtransaction.  The flag propagates up the subtransaction tree,
 * so the main transaction will correctly recognize the flag if all
 * intermediate subtransactions commit.  When it is InvalidSubTransactionId,
 * we either haven't made the TEMP namespace yet, or have successfully
 * committed its creation, depending on whether myTempNamespace is valid.
 */
static Oid      myTempNamespace = InvalidOid;

static Oid      myTempToastNamespace = InvalidOid;

static SubTransactionId myTempNamespaceSubID = InvalidSubTransactionId;

/*
 * This is the user's textual search path specification --- it's the value
 * of the GUC variable 'search_path'.
 */
char       *namespace_search_path = NULL;


/* Local functions */
static void recomputeNamespacePath(void);
static void AccessTempTableNamespace(bool force);
static void InitTempTableNamespace(void);
static void RemoveTempRelations(Oid tempNamespaceId);
static void RemoveTempRelationsCallback(int code, Datum arg);
static void NamespaceCallback(Datum arg, int cacheid, uint32 hashvalue);
static bool MatchNamedCall(HeapTuple proctup, int nargs, List *argnames,
                                                   int **argnumbers);


/*
 * RangeVarGetRelidExtended
 *              Given a RangeVar describing an existing relation,
 *              select the proper namespace and look up the relation OID.
 *
 * If the schema or relation is not found, return InvalidOid if flags contains
 * RVR_MISSING_OK, otherwise raise an error.
 *
 * If flags contains RVR_NOWAIT, throw an error if we'd have to wait for a
 * lock.
 *
 * If flags contains RVR_SKIP_LOCKED, return InvalidOid if we'd have to wait
 * for a lock.
 *
 * flags cannot contain both RVR_NOWAIT and RVR_SKIP_LOCKED.
 *
 * Note that if RVR_MISSING_OK and RVR_SKIP_LOCKED are both specified, a
 * return value of InvalidOid could either mean the relation is missing or it
 * could not be locked.
 *
 * Callback allows caller to check permissions or acquire additional locks
 * prior to grabbing the relation lock.
 */
Oid
RangeVarGetRelidExtended(const RangeVar *relation, LOCKMODE lockmode,
                                                 uint32 flags,
                                                 RangeVarGetRelidCallback callback, void *callback_arg)
{
        uint64          inval_count;
        Oid                     relId;
        Oid                     oldRelId = InvalidOid;
        bool            retry = false;
        bool            missing_ok = (flags & RVR_MISSING_OK) != 0;

        /* verify that flags do no conflict */
        Assert(!((flags & RVR_NOWAIT) && (flags & RVR_SKIP_LOCKED)));

        /*
         * We check the catalog name and then ignore it.
         */
        if (relation->catalogname)
        {
                if (strcmp(relation->catalogname, get_database_name(MyDatabaseId)) != 0)
                        ereport(ERROR,
                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                         errmsg("cross-database references are not implemented: \"%s.%s.%s\"",
                                                        relation->catalogname, relation->schemaname,
                                                        relation->relname)));
        }

        /*
         * DDL operations can change the results of a name lookup.  Since all such
         * operations will generate invalidation messages, we keep track of
         * whether any such messages show up while we're performing the operation,
         * and retry until either (1) no more invalidation messages show up or (2)
         * the answer doesn't change.
         *
         * But if lockmode = NoLock, then we assume that either the caller is OK
         * with the answer changing under them, or that they already hold some
         * appropriate lock, and therefore return the first answer we get without
         * checking for invalidation messages.  Also, if the requested lock is
         * already held, LockRelationOid will not AcceptInvalidationMessages, so
         * we may fail to notice a change.  We could protect against that case by
         * calling AcceptInvalidationMessages() before beginning this loop, but
         * that would add a significant amount overhead, so for now we don't.
         */
        for (;;)
        {
                /*
                 * Remember this value, so that, after looking up the relation name
                 * and locking its OID, we can check whether any invalidation messages
                 * have been processed that might require a do-over.
                 */
                inval_count = SharedInvalidMessageCounter;

                /*
                 * Some non-default relpersistence value may have been specified.  The
                 * parser never generates such a RangeVar in simple DML, but it can
                 * happen in contexts such as "CREATE TEMP TABLE foo (f1 int PRIMARY
                 * KEY)".  Such a command will generate an added CREATE INDEX
                 * operation, which must be careful to find the temp table, even when
                 * pg_temp is not first in the search path.
                 */
                if (relation->relpersistence == RELPERSISTENCE_TEMP)
                {
                        if (!OidIsValid(myTempNamespace))
                                relId = InvalidOid; /* this probably can't happen? */
                        else
                        {
                                if (relation->schemaname)
                                {
                                        Oid                     namespaceId;

                                        namespaceId = LookupExplicitNamespace(relation->schemaname, missing_ok);

                                        /*
                                         * For missing_ok, allow a non-existent schema name to
                                         * return InvalidOid.
                                         */
                                        if (namespaceId != myTempNamespace)
                                                ereport(ERROR,
                                                                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                                                                 errmsg("temporary tables cannot specify a schema name")));
                                }

                                relId = get_relname_relid(relation->relname, myTempNamespace);
                        }
                }
                else if (relation->schemaname)
                {
                        Oid                     namespaceId;

                        /* use exact schema given */
                        namespaceId = LookupExplicitNamespace(relation->schemaname, missing_ok);
                        if (missing_ok && !OidIsValid(namespaceId))
                                relId = InvalidOid;
                        else
                                relId = get_relname_relid(relation->relname, namespaceId);
                }
                else
                {
                        /* search the namespace path */
                        relId = RelnameGetRelid(relation->relname);
                }

                /*
                 * Invoke caller-supplied callback, if any.
                 *
                 * This callback is a good place to check permissions: we haven't
                 * taken the table lock yet (and it's really best to check permissions
                 * before locking anything!), but we've gotten far enough to know what
                 * OID we think we should lock.  Of course, concurrent DDL might
                 * change things while we're waiting for the lock, but in that case
                 * the callback will be invoked again for the new OID.
                 */
                if (callback)
                        callback(relation, relId, oldRelId, callback_arg);

                /*
                 * If no lock requested, we assume the caller knows what they're
                 * doing.  They should have already acquired a heavyweight lock on
                 * this relation earlier in the processing of this same statement, so
                 * it wouldn't be appropriate to AcceptInvalidationMessages() here, as
                 * that might pull the rug out from under them.
                 */
                if (lockmode == NoLock)
                        break;

                /*
                 * If, upon retry, we get back the same OID we did last time, then the
                 * invalidation messages we processed did not change the final answer.
                 * So we're done.
                 *
                 * If we got a different OID, we've locked the relation that used to
                 * have this name rather than the one that does now.  So release the
                 * lock.
                 */
                if (retry)
                {
                        if (relId == oldRelId)
                                break;
                        if (OidIsValid(oldRelId))
                                UnlockRelationOid(oldRelId, lockmode);
                }

                /*
                 * Lock relation.  This will also accept any pending invalidation
                 * messages.  If we got back InvalidOid, indicating not found, then
                 * there's nothing to lock, but we accept invalidation messages
                 * anyway, to flush any negative catcache entries that may be
                 * lingering.
                 */
                if (!OidIsValid(relId))
                        AcceptInvalidationMessages();
                else if (!(flags & (RVR_NOWAIT | RVR_SKIP_LOCKED)))
                        LockRelationOid(relId, lockmode);
                else if (!ConditionalLockRelationOid(relId, lockmode))
                {
                        int                     elevel = (flags & RVR_SKIP_LOCKED) ? DEBUG1 : ERROR;

                        if (relation->schemaname)
                                ereport(elevel,
                                                (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                                                 errmsg("could not obtain lock on relation \"%s.%s\"",
                                                                relation->schemaname, relation->relname)));
                        else
                                ereport(elevel,
                                                (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                                                 errmsg("could not obtain lock on relation \"%s\"",
                                                                relation->relname)));

                        return InvalidOid;
                }

                /*
                 * If no invalidation message were processed, we're done!
                 */
                if (inval_count == SharedInvalidMessageCounter)
                        break;

                /*
                 * Something may have changed.  Let's repeat the name lookup, to make
                 * sure this name still references the same relation it did
                 * previously.
                 */
                retry = true;
                oldRelId = relId;
        }

        if (!OidIsValid(relId))
        {
                int                     elevel = missing_ok ? DEBUG1 : ERROR;

                if (relation->schemaname)
                        ereport(elevel,
                                        (errcode(ERRCODE_UNDEFINED_TABLE),
                                         errmsg("relation \"%s.%s\" does not exist",
                                                        relation->schemaname, relation->relname)));
                else
                        ereport(elevel,
                                        (errcode(ERRCODE_UNDEFINED_TABLE),
                                         errmsg("relation \"%s\" does not exist",
                                                        relation->relname)));
        }
        return relId;
}

/*
 * RangeVarGetCreationNamespace
 *              Given a RangeVar describing a to-be-created relation,
 *              choose which namespace to create it in.
 *
 * Note: calling this may result in a CommandCounterIncrement operation.
 * That will happen on the first request for a temp table in any particular
 * backend run; we will need to either create or clean out the temp schema.
 */
Oid
RangeVarGetCreationNamespace(const RangeVar *newRelation)
{
        Oid                     namespaceId;

        /*
         * We check the catalog name and then ignore it.
         */
        if (newRelation->catalogname)
        {
                if (strcmp(newRelation->catalogname, get_database_name(MyDatabaseId)) != 0)
                        ereport(ERROR,
                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                         errmsg("cross-database references are not implemented: \"%s.%s.%s\"",
                                                        newRelation->catalogname, newRelation->schemaname,
                                                        newRelation->relname)));
        }

        if (newRelation->schemaname)
        {
                /* check for pg_temp alias */
                if (strcmp(newRelation->schemaname, "pg_temp") == 0)
                {
                        /* Initialize temp namespace */
                        AccessTempTableNamespace(false);
                        return myTempNamespace;
                }
                /* use exact schema given */
                namespaceId = get_namespace_oid(newRelation->schemaname, false);
                /* we do not check for USAGE rights here! */
        }
        else if (newRelation->relpersistence == RELPERSISTENCE_TEMP)
        {
                /* Initialize temp namespace */
                AccessTempTableNamespace(false);
                return myTempNamespace;
        }
        else
        {
                /* use the default creation namespace */
                recomputeNamespacePath();
                if (activeTempCreationPending)
                {
                        /* Need to initialize temp namespace */
                        AccessTempTableNamespace(true);
                        return myTempNamespace;
                }
                namespaceId = activeCreationNamespace;
                if (!OidIsValid(namespaceId))
                        ereport(ERROR,
                                        (errcode(ERRCODE_UNDEFINED_SCHEMA),
                                         errmsg("no schema has been selected to create in")));
        }

        /* Note: callers will check for CREATE rights when appropriate */

        return namespaceId;
}

/*
 * RangeVarGetAndCheckCreationNamespace
 *
 * This function returns the OID of the namespace in which a new relation
 * with a given name should be created.  If the user does not have CREATE
 * permission on the target namespace, this function will instead signal
 * an ERROR.
 *
 * If non-NULL, *existing_relation_id is set to the OID of any existing relation
 * with the same name which already exists in that namespace, or to InvalidOid
 * if no such relation exists.
 *
 * If lockmode != NoLock, the specified lock mode is acquired on the existing
 * relation, if any, provided that the current user owns the target relation.
 * However, if lockmode != NoLock and the user does not own the target
 * relation, we throw an ERROR, as we must not try to lock relations the
 * user does not have permissions on.
 *
 * As a side effect, this function acquires AccessShareLock on the target
 * namespace.  Without this, the namespace could be dropped before our
 * transaction commits, leaving behind relations with relnamespace pointing
 * to a no-longer-existent namespace.
 *
 * As a further side-effect, if the selected namespace is a temporary namespace,
 * we mark the RangeVar as RELPERSISTENCE_TEMP.
 */
Oid
RangeVarGetAndCheckCreationNamespace(RangeVar *relation,
                                                                         LOCKMODE lockmode,
                                                                         Oid *existing_relation_id)
{
        uint64          inval_count;
        Oid                     relid;
        Oid                     oldrelid = InvalidOid;
        Oid                     nspid;
        Oid                     oldnspid = InvalidOid;
        bool            retry = false;

        /*
         * We check the catalog name and then ignore it.
         */
        if (relation->catalogname)
        {
                if (strcmp(relation->catalogname, get_database_name(MyDatabaseId)) != 0)
                        ereport(ERROR,
                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                         errmsg("cross-database references are not implemented: \"%s.%s.%s\"",
                                                        relation->catalogname, relation->schemaname,
                                                        relation->relname)));
        }

        /*
         * As in RangeVarGetRelidExtended(), we guard against concurrent DDL
         * operations by tracking whether any invalidation messages are processed
         * while we're doing the name lookups and acquiring locks.  See comments
         * in that function for a more detailed explanation of this logic.
         */
        for (;;)
        {
                AclResult       aclresult;

                inval_count = SharedInvalidMessageCounter;

                /* Look up creation namespace and check for existing relation. */
                nspid = RangeVarGetCreationNamespace(relation);
                Assert(OidIsValid(nspid));
                if (existing_relation_id != NULL)
                        relid = get_relname_relid(relation->relname, nspid);
                else
                        relid = InvalidOid;

                /*
                 * In bootstrap processing mode, we don't bother with permissions or
                 * locking.  Permissions might not be working yet, and locking is
                 * unnecessary.
                 */
                if (IsBootstrapProcessingMode())
                        break;

                /* Check namespace permissions. */
                aclresult = pg_namespace_aclcheck(nspid, GetUserId(), ACL_CREATE);
                if (aclresult != ACLCHECK_OK)
                        aclcheck_error(aclresult, OBJECT_SCHEMA,
                                                   get_namespace_name(nspid));

                if (retry)
                {
                        /* If nothing changed, we're done. */
                        if (relid == oldrelid && nspid == oldnspid)
                                break;
                        /* If creation namespace has changed, give up old lock. */
                        if (nspid != oldnspid)
                                UnlockDatabaseObject(NamespaceRelationId, oldnspid, 0,
                                                                         AccessShareLock);
                        /* If name points to something different, give up old lock. */
                        if (relid != oldrelid && OidIsValid(oldrelid) && lockmode != NoLock)
                                UnlockRelationOid(oldrelid, lockmode);
                }

                /* Lock namespace. */
                if (nspid != oldnspid)
                        LockDatabaseObject(NamespaceRelationId, nspid, 0, AccessShareLock);

                /* Lock relation, if required if and we have permission. */
                if (lockmode != NoLock && OidIsValid(relid))
                {
                        if (!pg_class_ownercheck(relid, GetUserId()))
                                aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(get_rel_relkind(relid)),
                                                           relation->relname);
                        if (relid != oldrelid)
                                LockRelationOid(relid, lockmode);
                }

                /* If no invalidation message were processed, we're done! */
                if (inval_count == SharedInvalidMessageCounter)
                        break;

                /* Something may have changed, so recheck our work. */
                retry = true;
                oldrelid = relid;
                oldnspid = nspid;
        }

        RangeVarAdjustRelationPersistence(relation, nspid);
        if (existing_relation_id != NULL)
                *existing_relation_id = relid;
        return nspid;
}

/*
 * Adjust the relpersistence for an about-to-be-created relation based on the
 * creation namespace, and throw an error for invalid combinations.
 */
void
RangeVarAdjustRelationPersistence(RangeVar *newRelation, Oid nspid)
{
        switch (newRelation->relpersistence)
        {
                case RELPERSISTENCE_TEMP:
                        if (!isTempOrTempToastNamespace(nspid))
                        {
                                if (isAnyTempNamespace(nspid))
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                                                         errmsg("cannot create relations in temporary schemas of other sessions")));
                                else
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                                                         errmsg("cannot create temporary relation in non-temporary schema")));
                        }
                        break;
                case RELPERSISTENCE_PERMANENT:
                        if (isTempOrTempToastNamespace(nspid))
                                newRelation->relpersistence = RELPERSISTENCE_TEMP;
                        else if (isAnyTempNamespace(nspid))
                                ereport(ERROR,
                                                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                                                 errmsg("cannot create relations in temporary schemas of other sessions")));
                        break;
                default:
                        if (isAnyTempNamespace(nspid))
                                ereport(ERROR,
                                                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                                                 errmsg("only temporary relations may be created in temporary schemas")));
        }
}

/*
 * RelnameGetRelid
 *              Try to resolve an unqualified relation name.
 *              Returns OID if relation found in search path, else InvalidOid.
 */
Oid
RelnameGetRelid(const char *relname)
{
        Oid                     relid;
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);

                relid = get_relname_relid(relname, namespaceId);
                if (OidIsValid(relid))
                        return relid;
        }

        /* Not found in path */
        return InvalidOid;
}


/*
 * RelationIsVisible
 *              Determine whether a relation (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified relation name".
 */
bool
RelationIsVisible(Oid relid)
{
        HeapTuple       reltup;
        Form_pg_class relform;
        Oid                     relnamespace;
        bool            visible;

        reltup = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
        if (!HeapTupleIsValid(reltup))
                elog(ERROR, "cache lookup failed for relation %u", relid);
        relform = (Form_pg_class) GETSTRUCT(reltup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        relnamespace = relform->relnamespace;
        if (relnamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, relnamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another relation of the same name earlier in the path. So
                 * we must do a slow check for conflicting relations.
                 */
                char       *relname = NameStr(relform->relname);
                ListCell   *l;

                visible = false;
                foreach(l, activeSearchPath)
                {
                        Oid                     namespaceId = lfirst_oid(l);

                        if (namespaceId == relnamespace)
                        {
                                /* Found it first in path */
                                visible = true;
                                break;
                        }
                        if (OidIsValid(get_relname_relid(relname, namespaceId)))
                        {
                                /* Found something else first in path */
                                break;
                        }
                }
        }

        ReleaseSysCache(reltup);

        return visible;
}


/*
 * TypenameGetTypid
 *              Try to resolve an unqualified datatype name.
 *              Returns OID if type found in search path, else InvalidOid.
 *
 * This is essentially the same as RelnameGetRelid.
 */
Oid
TypenameGetTypid(const char *typname)
{
        Oid                     typid;
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);

                typid = GetSysCacheOid2(TYPENAMENSP, Anum_pg_type_oid,
                                                                PointerGetDatum(typname),
                                                                ObjectIdGetDatum(namespaceId));
                if (OidIsValid(typid))
                        return typid;
        }

        /* Not found in path */
        return InvalidOid;
}

/*
 * TypeIsVisible
 *              Determine whether a type (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified type name".
 */
bool
TypeIsVisible(Oid typid)
{
        HeapTuple       typtup;
        Form_pg_type typform;
        Oid                     typnamespace;
        bool            visible;

        typtup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typid));
        if (!HeapTupleIsValid(typtup))
                elog(ERROR, "cache lookup failed for type %u", typid);
        typform = (Form_pg_type) GETSTRUCT(typtup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        typnamespace = typform->typnamespace;
        if (typnamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, typnamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another type of the same name earlier in the path. So we
                 * must do a slow check for conflicting types.
                 */
                char       *typname = NameStr(typform->typname);
                ListCell   *l;

                visible = false;
                foreach(l, activeSearchPath)
                {
                        Oid                     namespaceId = lfirst_oid(l);

                        if (namespaceId == typnamespace)
                        {
                                /* Found it first in path */
                                visible = true;
                                break;
                        }
                        if (SearchSysCacheExists2(TYPENAMENSP,
                                                                          PointerGetDatum(typname),
                                                                          ObjectIdGetDatum(namespaceId)))
                        {
                                /* Found something else first in path */
                                break;
                        }
                }
        }

        ReleaseSysCache(typtup);

        return visible;
}


/*
 * FuncnameGetCandidates
 *              Given a possibly-qualified function name and argument count,
 *              retrieve a list of the possible matches.
 *
 * If nargs is -1, we return all functions matching the given name,
 * regardless of argument count.  (argnames must be NIL, and expand_variadic
 * and expand_defaults must be false, in this case.)
 *
 * If argnames isn't NIL, we are considering a named- or mixed-notation call,
 * and only functions having all the listed argument names will be returned.
 * (We assume that length(argnames) <= nargs and all the passed-in names are
 * distinct.)  The returned structs will include an argnumbers array showing
 * the actual argument index for each logical argument position.
 *
 * If expand_variadic is true, then variadic functions having the same number
 * or fewer arguments will be retrieved, with the variadic argument and any
 * additional argument positions filled with the variadic element type.
 * nvargs in the returned struct is set to the number of such arguments.
 * If expand_variadic is false, variadic arguments are not treated specially,
 * and the returned nvargs will always be zero.
 *
 * If expand_defaults is true, functions that could match after insertion of
 * default argument values will also be retrieved.  In this case the returned
 * structs could have nargs > passed-in nargs, and ndargs is set to the number
 * of additional args (which can be retrieved from the function's
 * proargdefaults entry).
 *
 * It is not possible for nvargs and ndargs to both be nonzero in the same
 * list entry, since default insertion allows matches to functions with more
 * than nargs arguments while the variadic transformation requires the same
 * number or less.
 *
 * When argnames isn't NIL, the returned args[] type arrays are not ordered
 * according to the functions' declarations, but rather according to the call:
 * first any positional arguments, then the named arguments, then defaulted
 * arguments (if needed and allowed by expand_defaults).  The argnumbers[]
 * array can be used to map this back to the catalog information.
 * argnumbers[k] is set to the proargtypes index of the k'th call argument.
 *
 * We search a single namespace if the function name is qualified, else
 * all namespaces in the search path.  In the multiple-namespace case,
 * we arrange for entries in earlier namespaces to mask identical entries in
 * later namespaces.
 *
 * When expanding variadics, we arrange for non-variadic functions to mask
 * variadic ones if the expanded argument list is the same.  It is still
 * possible for there to be conflicts between different variadic functions,
 * however.
 *
 * It is guaranteed that the return list will never contain multiple entries
 * with identical argument lists.  When expand_defaults is true, the entries
 * could have more than nargs positions, but we still guarantee that they are
 * distinct in the first nargs positions.  However, if argnames isn't NIL or
 * either expand_variadic or expand_defaults is true, there might be multiple
 * candidate functions that expand to identical argument lists.  Rather than
 * throw error here, we report such situations by returning a single entry
 * with oid = 0 that represents a set of such conflicting candidates.
 * The caller might end up discarding such an entry anyway, but if it selects
 * such an entry it should react as though the call were ambiguous.
 *
 * If missing_ok is true, an empty list (NULL) is returned if the name was
 * schema- qualified with a schema that does not exist.  Likewise if no
 * candidate is found for other reasons.
 */
FuncCandidateList
FuncnameGetCandidates(List *names, int nargs, List *argnames,
                                          bool expand_variadic, bool expand_defaults,
                                          bool missing_ok)
{
        FuncCandidateList resultList = NULL;
        bool            any_special = false;
        char       *schemaname;
        char       *funcname;
        Oid                     namespaceId;
        CatCList   *catlist;
        int                     i;

        /* check for caller error */
        Assert(nargs >= 0 || !(expand_variadic | expand_defaults));

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &funcname);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (!OidIsValid(namespaceId))
                        return NULL;
        }
        else
        {
                /* flag to indicate we need namespace search */
                namespaceId = InvalidOid;
                recomputeNamespacePath();
        }

        /* Search syscache by name only */
        catlist = SearchSysCacheList1(PROCNAMEARGSNSP, CStringGetDatum(funcname));

        for (i = 0; i < catlist->n_members; i++)
        {
                HeapTuple       proctup = &catlist->members[i]->tuple;
                Form_pg_proc procform = (Form_pg_proc) GETSTRUCT(proctup);
                int                     pronargs = procform->pronargs;
                int                     effective_nargs;
                int                     pathpos = 0;
                bool            variadic;
                bool            use_defaults;
                Oid                     va_elem_type;
                int                *argnumbers = NULL;
                FuncCandidateList newResult;

                if (OidIsValid(namespaceId))
                {
                        /* Consider only procs in specified namespace */
                        if (procform->pronamespace != namespaceId)
                                continue;
                }
                else
                {
                        /*
                         * Consider only procs that are in the search path and are not in
                         * the temp namespace.
                         */
                        ListCell   *nsp;

                        foreach(nsp, activeSearchPath)
                        {
                                if (procform->pronamespace == lfirst_oid(nsp) &&
                                        procform->pronamespace != myTempNamespace)
                                        break;
                                pathpos++;
                        }
                        if (nsp == NULL)
                                continue;               /* proc is not in search path */
                }

                if (argnames != NIL)
                {
                        /*
                         * Call uses named or mixed notation
                         *
                         * Named or mixed notation can match a variadic function only if
                         * expand_variadic is off; otherwise there is no way to match the
                         * presumed-nameless parameters expanded from the variadic array.
                         */
                        if (OidIsValid(procform->provariadic) && expand_variadic)
                                continue;
                        va_elem_type = InvalidOid;
                        variadic = false;

                        /*
                         * Check argument count.
                         */
                        Assert(nargs >= 0); /* -1 not supported with argnames */

                        if (pronargs > nargs && expand_defaults)
                        {
                                /* Ignore if not enough default expressions */
                                if (nargs + procform->pronargdefaults < pronargs)
                                        continue;
                                use_defaults = true;
                        }
                        else
                                use_defaults = false;

                        /* Ignore if it doesn't match requested argument count */
                        if (pronargs != nargs && !use_defaults)
                                continue;

                        /* Check for argument name match, generate positional mapping */
                        if (!MatchNamedCall(proctup, nargs, argnames,
                                                                &argnumbers))
                                continue;

                        /* Named argument matching is always "special" */
                        any_special = true;
                }
                else
                {
                        /*
                         * Call uses positional notation
                         *
                         * Check if function is variadic, and get variadic element type if
                         * so.  If expand_variadic is false, we should just ignore
                         * variadic-ness.
                         */
                        if (pronargs <= nargs && expand_variadic)
                        {
                                va_elem_type = procform->provariadic;
                                variadic = OidIsValid(va_elem_type);
                                any_special |= variadic;
                        }
                        else
                        {
                                va_elem_type = InvalidOid;
                                variadic = false;
                        }

                        /*
                         * Check if function can match by using parameter defaults.
                         */
                        if (pronargs > nargs && expand_defaults)
                        {
                                /* Ignore if not enough default expressions */
                                if (nargs + procform->pronargdefaults < pronargs)
                                        continue;
                                use_defaults = true;
                                any_special = true;
                        }
                        else
                                use_defaults = false;

                        /* Ignore if it doesn't match requested argument count */
                        if (nargs >= 0 && pronargs != nargs && !variadic && !use_defaults)
                                continue;
                }

                /*
                 * We must compute the effective argument list so that we can easily
                 * compare it to earlier results.  We waste a palloc cycle if it gets
                 * masked by an earlier result, but really that's a pretty infrequent
                 * case so it's not worth worrying about.
                 */
                effective_nargs = Max(pronargs, nargs);
                newResult = (FuncCandidateList)
                        palloc(offsetof(struct _FuncCandidateList, args) +
                                   effective_nargs * sizeof(Oid));
                newResult->pathpos = pathpos;
                newResult->oid = procform->oid;
                newResult->nargs = effective_nargs;
                newResult->argnumbers = argnumbers;
                if (argnumbers)
                {
                        /* Re-order the argument types into call's logical order */
                        Oid                *proargtypes = procform->proargtypes.values;
                        int                     i;

                        for (i = 0; i < pronargs; i++)
                                newResult->args[i] = proargtypes[argnumbers[i]];
                }
                else
                {
                        /* Simple positional case, just copy proargtypes as-is */
                        memcpy(newResult->args, procform->proargtypes.values,
                                   pronargs * sizeof(Oid));
                }
                if (variadic)
                {
                        int                     i;

                        newResult->nvargs = effective_nargs - pronargs + 1;
                        /* Expand variadic argument into N copies of element type */
                        for (i = pronargs - 1; i < effective_nargs; i++)
                                newResult->args[i] = va_elem_type;
                }
                else
                        newResult->nvargs = 0;
                newResult->ndargs = use_defaults ? pronargs - nargs : 0;

                /*
                 * Does it have the same arguments as something we already accepted?
                 * If so, decide what to do to avoid returning duplicate argument
                 * lists.  We can skip this check for the single-namespace case if no
                 * special (named, variadic or defaults) match has been made, since
                 * then the unique index on pg_proc guarantees all the matches have
                 * different argument lists.
                 */
                if (resultList != NULL &&
                        (any_special || !OidIsValid(namespaceId)))
                {
                        /*
                         * If we have an ordered list from SearchSysCacheList (the normal
                         * case), then any conflicting proc must immediately adjoin this
                         * one in the list, so we only need to look at the newest result
                         * item.  If we have an unordered list, we have to scan the whole
                         * result list.  Also, if either the current candidate or any
                         * previous candidate is a special match, we can't assume that
                         * conflicts are adjacent.
                         *
                         * We ignore defaulted arguments in deciding what is a match.
                         */
                        FuncCandidateList prevResult;

                        if (catlist->ordered && !any_special)
                        {
                                /* ndargs must be 0 if !any_special */
                                if (effective_nargs == resultList->nargs &&
                                        memcmp(newResult->args,
                                                   resultList->args,
                                                   effective_nargs * sizeof(Oid)) == 0)
                                        prevResult = resultList;
                                else
                                        prevResult = NULL;
                        }
                        else
                        {
                                int                     cmp_nargs = newResult->nargs - newResult->ndargs;

                                for (prevResult = resultList;
                                         prevResult;
                                         prevResult = prevResult->next)
                                {
                                        if (cmp_nargs == prevResult->nargs - prevResult->ndargs &&
                                                memcmp(newResult->args,
                                                           prevResult->args,
                                                           cmp_nargs * sizeof(Oid)) == 0)
                                                break;
                                }
                        }

                        if (prevResult)
                        {
                                /*
                                 * We have a match with a previous result.  Decide which one
                                 * to keep, or mark it ambiguous if we can't decide.  The
                                 * logic here is preference > 0 means prefer the old result,
                                 * preference < 0 means prefer the new, preference = 0 means
                                 * ambiguous.
                                 */
                                int                     preference;

                                if (pathpos != prevResult->pathpos)
                                {
                                        /*
                                         * Prefer the one that's earlier in the search path.
                                         */
                                        preference = pathpos - prevResult->pathpos;
                                }
                                else if (variadic && prevResult->nvargs == 0)
                                {
                                        /*
                                         * With variadic functions we could have, for example,
                                         * both foo(numeric) and foo(variadic numeric[]) in the
                                         * same namespace; if so we prefer the non-variadic match
                                         * on efficiency grounds.
                                         */
                                        preference = 1;
                                }
                                else if (!variadic && prevResult->nvargs > 0)
                                {
                                        preference = -1;
                                }
                                else
                                {
                                        /*----------
                                         * We can't decide.  This can happen with, for example,
                                         * both foo(numeric, variadic numeric[]) and
                                         * foo(variadic numeric[]) in the same namespace, or
                                         * both foo(int) and foo (int, int default something)
                                         * in the same namespace, or both foo(a int, b text)
                                         * and foo(b text, a int) in the same namespace.
                                         *----------
                                         */
                                        preference = 0;
                                }

                                if (preference > 0)
                                {
                                        /* keep previous result */
                                        pfree(newResult);
                                        continue;
                                }
                                else if (preference < 0)
                                {
                                        /* remove previous result from the list */
                                        if (prevResult == resultList)
                                                resultList = prevResult->next;
                                        else
                                        {
                                                FuncCandidateList prevPrevResult;

                                                for (prevPrevResult = resultList;
                                                         prevPrevResult;
                                                         prevPrevResult = prevPrevResult->next)
                                                {
                                                        if (prevResult == prevPrevResult->next)
                                                        {
                                                                prevPrevResult->next = prevResult->next;
                                                                break;
                                                        }
                                                }
                                                Assert(prevPrevResult); /* assert we found it */
                                        }
                                        pfree(prevResult);
                                        /* fall through to add newResult to list */
                                }
                                else
                                {
                                        /* mark old result as ambiguous, discard new */
                                        prevResult->oid = InvalidOid;
                                        pfree(newResult);
                                        continue;
                                }
                        }
                }

                /*
                 * Okay to add it to result list
                 */
                newResult->next = resultList;
                resultList = newResult;
        }

        ReleaseSysCacheList(catlist);

        return resultList;
}

/*
 * MatchNamedCall
 *              Given a pg_proc heap tuple and a call's list of argument names,
 *              check whether the function could match the call.
 *
 * The call could match if all supplied argument names are accepted by
 * the function, in positions after the last positional argument, and there
 * are defaults for all unsupplied arguments.
 *
 * The number of positional arguments is nargs - list_length(argnames).
 * Note caller has already done basic checks on argument count.
 *
 * On match, return true and fill *argnumbers with a palloc'd array showing
 * the mapping from call argument positions to actual function argument
 * numbers.  Defaulted arguments are included in this map, at positions
 * after the last supplied argument.
 */
static bool
MatchNamedCall(HeapTuple proctup, int nargs, List *argnames,
                           int **argnumbers)
{
        Form_pg_proc procform = (Form_pg_proc) GETSTRUCT(proctup);
        int                     pronargs = procform->pronargs;
        int                     numposargs = nargs - list_length(argnames);
        int                     pronallargs;
        Oid                *p_argtypes;
        char      **p_argnames;
        char       *p_argmodes;
        bool            arggiven[FUNC_MAX_ARGS];
        bool            isnull;
        int                     ap;                             /* call args position */
        int                     pp;                             /* proargs position */
        ListCell   *lc;

        Assert(argnames != NIL);
        Assert(numposargs >= 0);
        Assert(nargs <= pronargs);

        /* Ignore this function if its proargnames is null */
        (void) SysCacheGetAttr(PROCOID, proctup, Anum_pg_proc_proargnames,
                                                   &isnull);
        if (isnull)
                return false;

        /* OK, let's extract the argument names and types */
        pronallargs = get_func_arg_info(proctup,
                                                                        &p_argtypes, &p_argnames, &p_argmodes);
        Assert(p_argnames != NULL);

        /* initialize state for matching */
        *argnumbers = (int *) palloc(pronargs * sizeof(int));
        memset(arggiven, false, pronargs * sizeof(bool));

        /* there are numposargs positional args before the named args */
        for (ap = 0; ap < numposargs; ap++)
        {
                (*argnumbers)[ap] = ap;
                arggiven[ap] = true;
        }

        /* now examine the named args */
        foreach(lc, argnames)
        {
                char       *argname = (char *) lfirst(lc);
                bool            found;
                int                     i;

                pp = 0;
                found = false;
                for (i = 0; i < pronallargs; i++)
                {
                        /* consider only input parameters */
                        if (p_argmodes &&
                                (p_argmodes[i] != FUNC_PARAM_IN &&
                                 p_argmodes[i] != FUNC_PARAM_INOUT &&
                                 p_argmodes[i] != FUNC_PARAM_VARIADIC))
                                continue;
                        if (p_argnames[i] && strcmp(p_argnames[i], argname) == 0)
                        {
                                /* fail if argname matches a positional argument */
                                if (arggiven[pp])
                                        return false;
                                arggiven[pp] = true;
                                (*argnumbers)[ap] = pp;
                                found = true;
                                break;
                        }
                        /* increase pp only for input parameters */
                        pp++;
                }
                /* if name isn't in proargnames, fail */
                if (!found)
                        return false;
                ap++;
        }

        Assert(ap == nargs);            /* processed all actual parameters */

        /* Check for default arguments */
        if (nargs < pronargs)
        {
                int                     first_arg_with_default = pronargs - procform->pronargdefaults;

                for (pp = numposargs; pp < pronargs; pp++)
                {
                        if (arggiven[pp])
                                continue;
                        /* fail if arg not given and no default available */
                        if (pp < first_arg_with_default)
                                return false;
                        (*argnumbers)[ap++] = pp;
                }
        }

        Assert(ap == pronargs);         /* processed all function parameters */

        return true;
}

/*
 * FunctionIsVisible
 *              Determine whether a function (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified function name with exact argument matches".
 */
bool
FunctionIsVisible(Oid funcid)
{
        HeapTuple       proctup;
        Form_pg_proc procform;
        Oid                     pronamespace;
        bool            visible;

        proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
        if (!HeapTupleIsValid(proctup))
                elog(ERROR, "cache lookup failed for function %u", funcid);
        procform = (Form_pg_proc) GETSTRUCT(proctup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        pronamespace = procform->pronamespace;
        if (pronamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, pronamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another proc of the same name and arguments earlier in
                 * the path.  So we must do a slow check to see if this is the same
                 * proc that would be found by FuncnameGetCandidates.
                 */
                char       *proname = NameStr(procform->proname);
                int                     nargs = procform->pronargs;
                FuncCandidateList clist;

                visible = false;

                clist = FuncnameGetCandidates(list_make1(makeString(proname)),
                                                                          nargs, NIL, false, false, false);

                for (; clist; clist = clist->next)
                {
                        if (memcmp(clist->args, procform->proargtypes.values,
                                           nargs * sizeof(Oid)) == 0)
                        {
                                /* Found the expected entry; is it the right proc? */
                                visible = (clist->oid == funcid);
                                break;
                        }
                }
        }

        ReleaseSysCache(proctup);

        return visible;
}


/*
 * OpernameGetOprid
 *              Given a possibly-qualified operator name and exact input datatypes,
 *              look up the operator.  Returns InvalidOid if not found.
 *
 * Pass oprleft = InvalidOid for a prefix op, oprright = InvalidOid for
 * a postfix op.
 *
 * If the operator name is not schema-qualified, it is sought in the current
 * namespace search path.  If the name is schema-qualified and the given
 * schema does not exist, InvalidOid is returned.
 */
Oid
OpernameGetOprid(List *names, Oid oprleft, Oid oprright)
{
        char       *schemaname;
        char       *opername;
        CatCList   *catlist;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &opername);

        if (schemaname)
        {
                /* search only in exact schema given */
                Oid                     namespaceId;

                namespaceId = LookupExplicitNamespace(schemaname, true);
                if (OidIsValid(namespaceId))
                {
                        HeapTuple       opertup;

                        opertup = SearchSysCache4(OPERNAMENSP,
                                                                          CStringGetDatum(opername),
                                                                          ObjectIdGetDatum(oprleft),
                                                                          ObjectIdGetDatum(oprright),
                                                                          ObjectIdGetDatum(namespaceId));
                        if (HeapTupleIsValid(opertup))
                        {
                                Form_pg_operator operclass = (Form_pg_operator) GETSTRUCT(opertup);
                                Oid                     result = operclass->oid;

                                ReleaseSysCache(opertup);
                                return result;
                        }
                }

                return InvalidOid;
        }

        /* Search syscache by name and argument types */
        catlist = SearchSysCacheList3(OPERNAMENSP,
                                                                  CStringGetDatum(opername),
                                                                  ObjectIdGetDatum(oprleft),
                                                                  ObjectIdGetDatum(oprright));

        if (catlist->n_members == 0)
        {
                /* no hope, fall out early */
                ReleaseSysCacheList(catlist);
                return InvalidOid;
        }

        /*
         * We have to find the list member that is first in the search path, if
         * there's more than one.  This doubly-nested loop looks ugly, but in
         * practice there should usually be few catlist members.
         */
        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);
                int                     i;

                if (namespaceId == myTempNamespace)
                        continue;                       /* do not look in temp namespace */

                for (i = 0; i < catlist->n_members; i++)
                {
                        HeapTuple       opertup = &catlist->members[i]->tuple;
                        Form_pg_operator operform = (Form_pg_operator) GETSTRUCT(opertup);

                        if (operform->oprnamespace == namespaceId)
                        {
                                Oid                     result = operform->oid;

                                ReleaseSysCacheList(catlist);
                                return result;
                        }
                }
        }

        ReleaseSysCacheList(catlist);
        return InvalidOid;
}

/*
 * OpernameGetCandidates
 *              Given a possibly-qualified operator name and operator kind,
 *              retrieve a list of the possible matches.
 *
 * If oprkind is '\0', we return all operators matching the given name,
 * regardless of arguments.
 *
 * We search a single namespace if the operator name is qualified, else
 * all namespaces in the search path.  The return list will never contain
 * multiple entries with identical argument lists --- in the multiple-
 * namespace case, we arrange for entries in earlier namespaces to mask
 * identical entries in later namespaces.
 *
 * The returned items always have two args[] entries --- one or the other
 * will be InvalidOid for a prefix or postfix oprkind.  nargs is 2, too.
 */
FuncCandidateList
OpernameGetCandidates(List *names, char oprkind, bool missing_schema_ok)
{
        FuncCandidateList resultList = NULL;
        char       *resultSpace = NULL;
        int                     nextResult = 0;
        char       *schemaname;
        char       *opername;
        Oid                     namespaceId;
        CatCList   *catlist;
        int                     i;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &opername);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_schema_ok);
                if (missing_schema_ok && !OidIsValid(namespaceId))
                        return NULL;
        }
        else
        {
                /* flag to indicate we need namespace search */
                namespaceId = InvalidOid;
                recomputeNamespacePath();
        }

        /* Search syscache by name only */
        catlist = SearchSysCacheList1(OPERNAMENSP, CStringGetDatum(opername));

        /*
         * In typical scenarios, most if not all of the operators found by the
         * catcache search will end up getting returned; and there can be quite a
         * few, for common operator names such as '=' or '+'.  To reduce the time
         * spent in palloc, we allocate the result space as an array large enough
         * to hold all the operators.  The original coding of this routine did a
         * separate palloc for each operator, but profiling revealed that the
         * pallocs used an unreasonably large fraction of parsing time.
         */
#define SPACE_PER_OP MAXALIGN(offsetof(struct _FuncCandidateList, args) + \
                                                          2 * sizeof(Oid))

        if (catlist->n_members > 0)
                resultSpace = palloc(catlist->n_members * SPACE_PER_OP);

        for (i = 0; i < catlist->n_members; i++)
        {
                HeapTuple       opertup = &catlist->members[i]->tuple;
                Form_pg_operator operform = (Form_pg_operator) GETSTRUCT(opertup);
                int                     pathpos = 0;
                FuncCandidateList newResult;

                /* Ignore operators of wrong kind, if specific kind requested */
                if (oprkind && operform->oprkind != oprkind)
                        continue;

                if (OidIsValid(namespaceId))
                {
                        /* Consider only opers in specified namespace */
                        if (operform->oprnamespace != namespaceId)
                                continue;
                        /* No need to check args, they must all be different */
                }
                else
                {
                        /*
                         * Consider only opers that are in the search path and are not in
                         * the temp namespace.
                         */
                        ListCell   *nsp;

                        foreach(nsp, activeSearchPath)
                        {
                                if (operform->oprnamespace == lfirst_oid(nsp) &&
                                        operform->oprnamespace != myTempNamespace)
                                        break;
                                pathpos++;
                        }
                        if (nsp == NULL)
                                continue;               /* oper is not in search path */

                        /*
                         * Okay, it's in the search path, but does it have the same
                         * arguments as something we already accepted?  If so, keep only
                         * the one that appears earlier in the search path.
                         *
                         * If we have an ordered list from SearchSysCacheList (the normal
                         * case), then any conflicting oper must immediately adjoin this
                         * one in the list, so we only need to look at the newest result
                         * item.  If we have an unordered list, we have to scan the whole
                         * result list.
                         */
                        if (resultList)
                        {
                                FuncCandidateList prevResult;

                                if (catlist->ordered)
                                {
                                        if (operform->oprleft == resultList->args[0] &&
                                                operform->oprright == resultList->args[1])
                                                prevResult = resultList;
                                        else
                                                prevResult = NULL;
                                }
                                else
                                {
                                        for (prevResult = resultList;
                                                 prevResult;
                                                 prevResult = prevResult->next)
                                        {
                                                if (operform->oprleft == prevResult->args[0] &&
                                                        operform->oprright == prevResult->args[1])
                                                        break;
                                        }
                                }
                                if (prevResult)
                                {
                                        /* We have a match with a previous result */
                                        Assert(pathpos != prevResult->pathpos);
                                        if (pathpos > prevResult->pathpos)
                                                continue;       /* keep previous result */
                                        /* replace previous result */
                                        prevResult->pathpos = pathpos;
                                        prevResult->oid = operform->oid;
                                        continue;       /* args are same, of course */
                                }
                        }
                }

                /*
                 * Okay to add it to result list
                 */
                newResult = (FuncCandidateList) (resultSpace + nextResult);
                nextResult += SPACE_PER_OP;

                newResult->pathpos = pathpos;
                newResult->oid = operform->oid;
                newResult->nargs = 2;
                newResult->nvargs = 0;
                newResult->ndargs = 0;
                newResult->argnumbers = NULL;
                newResult->args[0] = operform->oprleft;
                newResult->args[1] = operform->oprright;
                newResult->next = resultList;
                resultList = newResult;
        }

        ReleaseSysCacheList(catlist);

        return resultList;
}

/*
 * OperatorIsVisible
 *              Determine whether an operator (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified operator name with exact argument matches".
 */
bool
OperatorIsVisible(Oid oprid)
{
        HeapTuple       oprtup;
        Form_pg_operator oprform;
        Oid                     oprnamespace;
        bool            visible;

        oprtup = SearchSysCache1(OPEROID, ObjectIdGetDatum(oprid));
        if (!HeapTupleIsValid(oprtup))
                elog(ERROR, "cache lookup failed for operator %u", oprid);
        oprform = (Form_pg_operator) GETSTRUCT(oprtup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        oprnamespace = oprform->oprnamespace;
        if (oprnamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, oprnamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another operator of the same name and arguments earlier
                 * in the path.  So we must do a slow check to see if this is the same
                 * operator that would be found by OpernameGetOprid.
                 */
                char       *oprname = NameStr(oprform->oprname);

                visible = (OpernameGetOprid(list_make1(makeString(oprname)),
                                                                        oprform->oprleft, oprform->oprright)
                                   == oprid);
        }

        ReleaseSysCache(oprtup);

        return visible;
}


/*
 * OpclassnameGetOpcid
 *              Try to resolve an unqualified index opclass name.
 *              Returns OID if opclass found in search path, else InvalidOid.
 *
 * This is essentially the same as TypenameGetTypid, but we have to have
 * an extra argument for the index AM OID.
 */
Oid
OpclassnameGetOpcid(Oid amid, const char *opcname)
{
        Oid                     opcid;
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);

                if (namespaceId == myTempNamespace)
                        continue;                       /* do not look in temp namespace */

                opcid = GetSysCacheOid3(CLAAMNAMENSP, Anum_pg_opclass_oid,
                                                                ObjectIdGetDatum(amid),
                                                                PointerGetDatum(opcname),
                                                                ObjectIdGetDatum(namespaceId));
                if (OidIsValid(opcid))
                        return opcid;
        }

        /* Not found in path */
        return InvalidOid;
}

/*
 * OpclassIsVisible
 *              Determine whether an opclass (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified opclass name".
 */
bool
OpclassIsVisible(Oid opcid)
{
        HeapTuple       opctup;
        Form_pg_opclass opcform;
        Oid                     opcnamespace;
        bool            visible;

        opctup = SearchSysCache1(CLAOID, ObjectIdGetDatum(opcid));
        if (!HeapTupleIsValid(opctup))
                elog(ERROR, "cache lookup failed for opclass %u", opcid);
        opcform = (Form_pg_opclass) GETSTRUCT(opctup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        opcnamespace = opcform->opcnamespace;
        if (opcnamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, opcnamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another opclass of the same name earlier in the path. So
                 * we must do a slow check to see if this opclass would be found by
                 * OpclassnameGetOpcid.
                 */
                char       *opcname = NameStr(opcform->opcname);

                visible = (OpclassnameGetOpcid(opcform->opcmethod, opcname) == opcid);
        }

        ReleaseSysCache(opctup);

        return visible;
}

/*
 * OpfamilynameGetOpfid
 *              Try to resolve an unqualified index opfamily name.
 *              Returns OID if opfamily found in search path, else InvalidOid.
 *
 * This is essentially the same as TypenameGetTypid, but we have to have
 * an extra argument for the index AM OID.
 */
Oid
OpfamilynameGetOpfid(Oid amid, const char *opfname)
{
        Oid                     opfid;
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);

                if (namespaceId == myTempNamespace)
                        continue;                       /* do not look in temp namespace */

                opfid = GetSysCacheOid3(OPFAMILYAMNAMENSP, Anum_pg_opfamily_oid,
                                                                ObjectIdGetDatum(amid),
                                                                PointerGetDatum(opfname),
                                                                ObjectIdGetDatum(namespaceId));
                if (OidIsValid(opfid))
                        return opfid;
        }

        /* Not found in path */
        return InvalidOid;
}

/*
 * OpfamilyIsVisible
 *              Determine whether an opfamily (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified opfamily name".
 */
bool
OpfamilyIsVisible(Oid opfid)
{
        HeapTuple       opftup;
        Form_pg_opfamily opfform;
        Oid                     opfnamespace;
        bool            visible;

        opftup = SearchSysCache1(OPFAMILYOID, ObjectIdGetDatum(opfid));
        if (!HeapTupleIsValid(opftup))
                elog(ERROR, "cache lookup failed for opfamily %u", opfid);
        opfform = (Form_pg_opfamily) GETSTRUCT(opftup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        opfnamespace = opfform->opfnamespace;
        if (opfnamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, opfnamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another opfamily of the same name earlier in the path. So
                 * we must do a slow check to see if this opfamily would be found by
                 * OpfamilynameGetOpfid.
                 */
                char       *opfname = NameStr(opfform->opfname);

                visible = (OpfamilynameGetOpfid(opfform->opfmethod, opfname) == opfid);
        }

        ReleaseSysCache(opftup);

        return visible;
}

/*
 * lookup_collation
 *              If there's a collation of the given name/namespace, and it works
 *              with the given encoding, return its OID.  Else return InvalidOid.
 */
static Oid
lookup_collation(const char *collname, Oid collnamespace, int32 encoding)
{
        Oid                     collid;
        HeapTuple       colltup;
        Form_pg_collation collform;

        /* Check for encoding-specific entry (exact match) */
        collid = GetSysCacheOid3(COLLNAMEENCNSP, Anum_pg_collation_oid,
                                                         PointerGetDatum(collname),
                                                         Int32GetDatum(encoding),
                                                         ObjectIdGetDatum(collnamespace));
        if (OidIsValid(collid))
                return collid;

        /*
         * Check for any-encoding entry.  This takes a bit more work: while libc
         * collations with collencoding = -1 do work with all encodings, ICU
         * collations only work with certain encodings, so we have to check that
         * aspect before deciding it's a match.
         */
        colltup = SearchSysCache3(COLLNAMEENCNSP,
                                                          PointerGetDatum(collname),
                                                          Int32GetDatum(-1),
                                                          ObjectIdGetDatum(collnamespace));
        if (!HeapTupleIsValid(colltup))
                return InvalidOid;
        collform = (Form_pg_collation) GETSTRUCT(colltup);
        if (collform->collprovider == COLLPROVIDER_ICU)
        {
                if (is_encoding_supported_by_icu(encoding))
                        collid = collform->oid;
                else
                        collid = InvalidOid;
        }
        else
        {
                collid = collform->oid;
        }
        ReleaseSysCache(colltup);
        return collid;
}

/*
 * CollationGetCollid
 *              Try to resolve an unqualified collation name.
 *              Returns OID if collation found in search path, else InvalidOid.
 *
 * Note that this will only find collations that work with the current
 * database's encoding.
 */
Oid
CollationGetCollid(const char *collname)
{
        int32           dbencoding = GetDatabaseEncoding();
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);
                Oid                     collid;

                if (namespaceId == myTempNamespace)
                        continue;                       /* do not look in temp namespace */

                collid = lookup_collation(collname, namespaceId, dbencoding);
                if (OidIsValid(collid))
                        return collid;
        }

        /* Not found in path */
        return InvalidOid;
}

/*
 * CollationIsVisible
 *              Determine whether a collation (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified collation name".
 *
 * Note that only collations that work with the current database's encoding
 * will be considered visible.
 */
bool
CollationIsVisible(Oid collid)
{
        HeapTuple       colltup;
        Form_pg_collation collform;
        Oid                     collnamespace;
        bool            visible;

        colltup = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
        if (!HeapTupleIsValid(colltup))
                elog(ERROR, "cache lookup failed for collation %u", collid);
        collform = (Form_pg_collation) GETSTRUCT(colltup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        collnamespace = collform->collnamespace;
        if (collnamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, collnamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another collation of the same name earlier in the path,
                 * or it might not work with the current DB encoding.  So we must do a
                 * slow check to see if this collation would be found by
                 * CollationGetCollid.
                 */
                char       *collname = NameStr(collform->collname);

                visible = (CollationGetCollid(collname) == collid);
        }

        ReleaseSysCache(colltup);

        return visible;
}


/*
 * ConversionGetConid
 *              Try to resolve an unqualified conversion name.
 *              Returns OID if conversion found in search path, else InvalidOid.
 *
 * This is essentially the same as RelnameGetRelid.
 */
Oid
ConversionGetConid(const char *conname)
{
        Oid                     conid;
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);

                if (namespaceId == myTempNamespace)
                        continue;                       /* do not look in temp namespace */

                conid = GetSysCacheOid2(CONNAMENSP, Anum_pg_conversion_oid,
                                                                PointerGetDatum(conname),
                                                                ObjectIdGetDatum(namespaceId));
                if (OidIsValid(conid))
                        return conid;
        }

        /* Not found in path */
        return InvalidOid;
}

/*
 * ConversionIsVisible
 *              Determine whether a conversion (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified conversion name".
 */
bool
ConversionIsVisible(Oid conid)
{
        HeapTuple       contup;
        Form_pg_conversion conform;
        Oid                     connamespace;
        bool            visible;

        contup = SearchSysCache1(CONVOID, ObjectIdGetDatum(conid));
        if (!HeapTupleIsValid(contup))
                elog(ERROR, "cache lookup failed for conversion %u", conid);
        conform = (Form_pg_conversion) GETSTRUCT(contup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        connamespace = conform->connamespace;
        if (connamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, connamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another conversion of the same name earlier in the path.
                 * So we must do a slow check to see if this conversion would be found
                 * by ConversionGetConid.
                 */
                char       *conname = NameStr(conform->conname);

                visible = (ConversionGetConid(conname) == conid);
        }

        ReleaseSysCache(contup);

        return visible;
}

/*
 * get_statistics_object_oid - find a statistics object by possibly qualified name
 *
 * If not found, returns InvalidOid if missing_ok, else throws error
 */
Oid
get_statistics_object_oid(List *names, bool missing_ok)
{
        char       *schemaname;
        char       *stats_name;
        Oid                     namespaceId;
        Oid                     stats_oid = InvalidOid;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &stats_name);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (missing_ok && !OidIsValid(namespaceId))
                        stats_oid = InvalidOid;
                else
                        stats_oid = GetSysCacheOid2(STATEXTNAMENSP, Anum_pg_statistic_ext_oid,
                                                                                PointerGetDatum(stats_name),
                                                                                ObjectIdGetDatum(namespaceId));
        }
        else
        {
                /* search for it in search path */
                recomputeNamespacePath();

                foreach(l, activeSearchPath)
                {
                        namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */
                        stats_oid = GetSysCacheOid2(STATEXTNAMENSP, Anum_pg_statistic_ext_oid,
                                                                                PointerGetDatum(stats_name),
                                                                                ObjectIdGetDatum(namespaceId));
                        if (OidIsValid(stats_oid))
                                break;
                }
        }

        if (!OidIsValid(stats_oid) && !missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("statistics object \"%s\" does not exist",
                                                NameListToString(names))));

        return stats_oid;
}

/*
 * StatisticsObjIsVisible
 *              Determine whether a statistics object (identified by OID) is visible in
 *              the current search path.  Visible means "would be found by searching
 *              for the unqualified statistics object name".
 */
bool
StatisticsObjIsVisible(Oid relid)
{
        HeapTuple       stxtup;
        Form_pg_statistic_ext stxform;
        Oid                     stxnamespace;
        bool            visible;

        stxtup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(relid));
        if (!HeapTupleIsValid(stxtup))
                elog(ERROR, "cache lookup failed for statistics object %u", relid);
        stxform = (Form_pg_statistic_ext) GETSTRUCT(stxtup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        stxnamespace = stxform->stxnamespace;
        if (stxnamespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, stxnamespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another statistics object of the same name earlier in the
                 * path. So we must do a slow check for conflicting objects.
                 */
                char       *stxname = NameStr(stxform->stxname);
                ListCell   *l;

                visible = false;
                foreach(l, activeSearchPath)
                {
                        Oid                     namespaceId = lfirst_oid(l);

                        if (namespaceId == stxnamespace)
                        {
                                /* Found it first in path */
                                visible = true;
                                break;
                        }
                        if (SearchSysCacheExists2(STATEXTNAMENSP,
                                                                          PointerGetDatum(stxname),
                                                                          ObjectIdGetDatum(namespaceId)))
                        {
                                /* Found something else first in path */
                                break;
                        }
                }
        }

        ReleaseSysCache(stxtup);

        return visible;
}

/*
 * get_ts_parser_oid - find a TS parser by possibly qualified name
 *
 * If not found, returns InvalidOid if missing_ok, else throws error
 */
Oid
get_ts_parser_oid(List *names, bool missing_ok)
{
        char       *schemaname;
        char       *parser_name;
        Oid                     namespaceId;
        Oid                     prsoid = InvalidOid;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &parser_name);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (missing_ok && !OidIsValid(namespaceId))
                        prsoid = InvalidOid;
                else
                        prsoid = GetSysCacheOid2(TSPARSERNAMENSP, Anum_pg_ts_parser_oid,
                                                                         PointerGetDatum(parser_name),
                                                                         ObjectIdGetDatum(namespaceId));
        }
        else
        {
                /* search for it in search path */
                recomputeNamespacePath();

                foreach(l, activeSearchPath)
                {
                        namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        prsoid = GetSysCacheOid2(TSPARSERNAMENSP, Anum_pg_ts_parser_oid,
                                                                         PointerGetDatum(parser_name),
                                                                         ObjectIdGetDatum(namespaceId));
                        if (OidIsValid(prsoid))
                                break;
                }
        }

        if (!OidIsValid(prsoid) && !missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("text search parser \"%s\" does not exist",
                                                NameListToString(names))));

        return prsoid;
}

/*
 * TSParserIsVisible
 *              Determine whether a parser (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified parser name".
 */
bool
TSParserIsVisible(Oid prsId)
{
        HeapTuple       tup;
        Form_pg_ts_parser form;
        Oid                     namespace;
        bool            visible;

        tup = SearchSysCache1(TSPARSEROID, ObjectIdGetDatum(prsId));
        if (!HeapTupleIsValid(tup))
                elog(ERROR, "cache lookup failed for text search parser %u", prsId);
        form = (Form_pg_ts_parser) GETSTRUCT(tup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        namespace = form->prsnamespace;
        if (namespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, namespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another parser of the same name earlier in the path. So
                 * we must do a slow check for conflicting parsers.
                 */
                char       *name = NameStr(form->prsname);
                ListCell   *l;

                visible = false;
                foreach(l, activeSearchPath)
                {
                        Oid                     namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        if (namespaceId == namespace)
                        {
                                /* Found it first in path */
                                visible = true;
                                break;
                        }
                        if (SearchSysCacheExists2(TSPARSERNAMENSP,
                                                                          PointerGetDatum(name),
                                                                          ObjectIdGetDatum(namespaceId)))
                        {
                                /* Found something else first in path */
                                break;
                        }
                }
        }

        ReleaseSysCache(tup);

        return visible;
}

/*
 * get_ts_dict_oid - find a TS dictionary by possibly qualified name
 *
 * If not found, returns InvalidOid if failOK, else throws error
 */
Oid
get_ts_dict_oid(List *names, bool missing_ok)
{
        char       *schemaname;
        char       *dict_name;
        Oid                     namespaceId;
        Oid                     dictoid = InvalidOid;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &dict_name);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (missing_ok && !OidIsValid(namespaceId))
                        dictoid = InvalidOid;
                else
                        dictoid = GetSysCacheOid2(TSDICTNAMENSP, Anum_pg_ts_dict_oid,
                                                                          PointerGetDatum(dict_name),
                                                                          ObjectIdGetDatum(namespaceId));
        }
        else
        {
                /* search for it in search path */
                recomputeNamespacePath();

                foreach(l, activeSearchPath)
                {
                        namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        dictoid = GetSysCacheOid2(TSDICTNAMENSP, Anum_pg_ts_dict_oid,
                                                                          PointerGetDatum(dict_name),
                                                                          ObjectIdGetDatum(namespaceId));
                        if (OidIsValid(dictoid))
                                break;
                }
        }

        if (!OidIsValid(dictoid) && !missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("text search dictionary \"%s\" does not exist",
                                                NameListToString(names))));

        return dictoid;
}

/*
 * TSDictionaryIsVisible
 *              Determine whether a dictionary (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified dictionary name".
 */
bool
TSDictionaryIsVisible(Oid dictId)
{
        HeapTuple       tup;
        Form_pg_ts_dict form;
        Oid                     namespace;
        bool            visible;

        tup = SearchSysCache1(TSDICTOID, ObjectIdGetDatum(dictId));
        if (!HeapTupleIsValid(tup))
                elog(ERROR, "cache lookup failed for text search dictionary %u",
                         dictId);
        form = (Form_pg_ts_dict) GETSTRUCT(tup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        namespace = form->dictnamespace;
        if (namespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, namespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another dictionary of the same name earlier in the path.
                 * So we must do a slow check for conflicting dictionaries.
                 */
                char       *name = NameStr(form->dictname);
                ListCell   *l;

                visible = false;
                foreach(l, activeSearchPath)
                {
                        Oid                     namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        if (namespaceId == namespace)
                        {
                                /* Found it first in path */
                                visible = true;
                                break;
                        }
                        if (SearchSysCacheExists2(TSDICTNAMENSP,
                                                                          PointerGetDatum(name),
                                                                          ObjectIdGetDatum(namespaceId)))
                        {
                                /* Found something else first in path */
                                break;
                        }
                }
        }

        ReleaseSysCache(tup);

        return visible;
}

/*
 * get_ts_template_oid - find a TS template by possibly qualified name
 *
 * If not found, returns InvalidOid if missing_ok, else throws error
 */
Oid
get_ts_template_oid(List *names, bool missing_ok)
{
        char       *schemaname;
        char       *template_name;
        Oid                     namespaceId;
        Oid                     tmploid = InvalidOid;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &template_name);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (missing_ok && !OidIsValid(namespaceId))
                        tmploid = InvalidOid;
                else
                        tmploid = GetSysCacheOid2(TSTEMPLATENAMENSP, Anum_pg_ts_template_oid,
                                                                          PointerGetDatum(template_name),
                                                                          ObjectIdGetDatum(namespaceId));
        }
        else
        {
                /* search for it in search path */
                recomputeNamespacePath();

                foreach(l, activeSearchPath)
                {
                        namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        tmploid = GetSysCacheOid2(TSTEMPLATENAMENSP, Anum_pg_ts_template_oid,
                                                                          PointerGetDatum(template_name),
                                                                          ObjectIdGetDatum(namespaceId));
                        if (OidIsValid(tmploid))
                                break;
                }
        }

        if (!OidIsValid(tmploid) && !missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("text search template \"%s\" does not exist",
                                                NameListToString(names))));

        return tmploid;
}

/*
 * TSTemplateIsVisible
 *              Determine whether a template (identified by OID) is visible in the
 *              current search path.  Visible means "would be found by searching
 *              for the unqualified template name".
 */
bool
TSTemplateIsVisible(Oid tmplId)
{
        HeapTuple       tup;
        Form_pg_ts_template form;
        Oid                     namespace;
        bool            visible;

        tup = SearchSysCache1(TSTEMPLATEOID, ObjectIdGetDatum(tmplId));
        if (!HeapTupleIsValid(tup))
                elog(ERROR, "cache lookup failed for text search template %u", tmplId);
        form = (Form_pg_ts_template) GETSTRUCT(tup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        namespace = form->tmplnamespace;
        if (namespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, namespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another template of the same name earlier in the path. So
                 * we must do a slow check for conflicting templates.
                 */
                char       *name = NameStr(form->tmplname);
                ListCell   *l;

                visible = false;
                foreach(l, activeSearchPath)
                {
                        Oid                     namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        if (namespaceId == namespace)
                        {
                                /* Found it first in path */
                                visible = true;
                                break;
                        }
                        if (SearchSysCacheExists2(TSTEMPLATENAMENSP,
                                                                          PointerGetDatum(name),
                                                                          ObjectIdGetDatum(namespaceId)))
                        {
                                /* Found something else first in path */
                                break;
                        }
                }
        }

        ReleaseSysCache(tup);

        return visible;
}

/*
 * get_ts_config_oid - find a TS config by possibly qualified name
 *
 * If not found, returns InvalidOid if missing_ok, else throws error
 */
Oid
get_ts_config_oid(List *names, bool missing_ok)
{
        char       *schemaname;
        char       *config_name;
        Oid                     namespaceId;
        Oid                     cfgoid = InvalidOid;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, &config_name);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (missing_ok && !OidIsValid(namespaceId))
                        cfgoid = InvalidOid;
                else
                        cfgoid = GetSysCacheOid2(TSCONFIGNAMENSP, Anum_pg_ts_config_oid,
                                                                         PointerGetDatum(config_name),
                                                                         ObjectIdGetDatum(namespaceId));
        }
        else
        {
                /* search for it in search path */
                recomputeNamespacePath();

                foreach(l, activeSearchPath)
                {
                        namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        cfgoid = GetSysCacheOid2(TSCONFIGNAMENSP, Anum_pg_ts_config_oid,
                                                                         PointerGetDatum(config_name),
                                                                         ObjectIdGetDatum(namespaceId));
                        if (OidIsValid(cfgoid))
                                break;
                }
        }

        if (!OidIsValid(cfgoid) && !missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("text search configuration \"%s\" does not exist",
                                                NameListToString(names))));

        return cfgoid;
}

/*
 * TSConfigIsVisible
 *              Determine whether a text search configuration (identified by OID)
 *              is visible in the current search path.  Visible means "would be found
 *              by searching for the unqualified text search configuration name".
 */
bool
TSConfigIsVisible(Oid cfgid)
{
        HeapTuple       tup;
        Form_pg_ts_config form;
        Oid                     namespace;
        bool            visible;

        tup = SearchSysCache1(TSCONFIGOID, ObjectIdGetDatum(cfgid));
        if (!HeapTupleIsValid(tup))
                elog(ERROR, "cache lookup failed for text search configuration %u",
                         cfgid);
        form = (Form_pg_ts_config) GETSTRUCT(tup);

        recomputeNamespacePath();

        /*
         * Quick check: if it ain't in the path at all, it ain't visible. Items in
         * the system namespace are surely in the path and so we needn't even do
         * list_member_oid() for them.
         */
        namespace = form->cfgnamespace;
        if (namespace != PG_CATALOG_NAMESPACE &&
                !list_member_oid(activeSearchPath, namespace))
                visible = false;
        else
        {
                /*
                 * If it is in the path, it might still not be visible; it could be
                 * hidden by another configuration of the same name earlier in the
                 * path. So we must do a slow check for conflicting configurations.
                 */
                char       *name = NameStr(form->cfgname);
                ListCell   *l;

                visible = false;
                foreach(l, activeSearchPath)
                {
                        Oid                     namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        if (namespaceId == namespace)
                        {
                                /* Found it first in path */
                                visible = true;
                                break;
                        }
                        if (SearchSysCacheExists2(TSCONFIGNAMENSP,
                                                                          PointerGetDatum(name),
                                                                          ObjectIdGetDatum(namespaceId)))
                        {
                                /* Found something else first in path */
                                break;
                        }
                }
        }

        ReleaseSysCache(tup);

        return visible;
}


/*
 * DeconstructQualifiedName
 *              Given a possibly-qualified name expressed as a list of String nodes,
 *              extract the schema name and object name.
 *
 * *nspname_p is set to NULL if there is no explicit schema name.
 */
void
DeconstructQualifiedName(List *names,
                                                 char **nspname_p,
                                                 char **objname_p)
{
        char       *catalogname;
        char       *schemaname = NULL;
        char       *objname = NULL;

        switch (list_length(names))
        {
                case 1:
                        objname = strVal(linitial(names));
                        break;
                case 2:
                        schemaname = strVal(linitial(names));
                        objname = strVal(lsecond(names));
                        break;
                case 3:
                        catalogname = strVal(linitial(names));
                        schemaname = strVal(lsecond(names));
                        objname = strVal(lthird(names));

                        /*
                         * We check the catalog name and then ignore it.
                         */
                        if (strcmp(catalogname, get_database_name(MyDatabaseId)) != 0)
                                ereport(ERROR,
                                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                                 errmsg("cross-database references are not implemented: %s",
                                                                NameListToString(names))));
                        break;
                default:
                        ereport(ERROR,
                                        (errcode(ERRCODE_SYNTAX_ERROR),
                                         errmsg("improper qualified name (too many dotted names): %s",
                                                        NameListToString(names))));
                        break;
        }

        *nspname_p = schemaname;
        *objname_p = objname;
}

/*
 * LookupNamespaceNoError
 *              Look up a schema name.
 *
 * Returns the namespace OID, or InvalidOid if not found.
 *
 * Note this does NOT perform any permissions check --- callers are
 * responsible for being sure that an appropriate check is made.
 * In the majority of cases LookupExplicitNamespace is preferable.
 */
Oid
LookupNamespaceNoError(const char *nspname)
{
        /* check for pg_temp alias */
        if (strcmp(nspname, "pg_temp") == 0)
        {
                if (OidIsValid(myTempNamespace))
                {
                        InvokeNamespaceSearchHook(myTempNamespace, true);
                        return myTempNamespace;
                }

                /*
                 * Since this is used only for looking up existing objects, there is
                 * no point in trying to initialize the temp namespace here; and doing
                 * so might create problems for some callers. Just report "not found".
                 */
                return InvalidOid;
        }

        return get_namespace_oid(nspname, true);
}

/*
 * LookupExplicitNamespace
 *              Process an explicitly-specified schema name: look up the schema
 *              and verify we have USAGE (lookup) rights in it.
 *
 * Returns the namespace OID
 */
Oid
LookupExplicitNamespace(const char *nspname, bool missing_ok)
{
        Oid                     namespaceId;
        AclResult       aclresult;

        /* check for pg_temp alias */
        if (strcmp(nspname, "pg_temp") == 0)
        {
                if (OidIsValid(myTempNamespace))
                        return myTempNamespace;

                /*
                 * Since this is used only for looking up existing objects, there is
                 * no point in trying to initialize the temp namespace here; and doing
                 * so might create problems for some callers --- just fall through.
                 */
        }

        namespaceId = get_namespace_oid(nspname, missing_ok);
        if (missing_ok && !OidIsValid(namespaceId))
                return InvalidOid;

        aclresult = pg_namespace_aclcheck(namespaceId, GetUserId(), ACL_USAGE);
        if (aclresult != ACLCHECK_OK)
                aclcheck_error(aclresult, OBJECT_SCHEMA,
                                           nspname);
        /* Schema search hook for this lookup */
        InvokeNamespaceSearchHook(namespaceId, true);

        return namespaceId;
}

/*
 * LookupCreationNamespace
 *              Look up the schema and verify we have CREATE rights on it.
 *
 * This is just like LookupExplicitNamespace except for the different
 * permission check, and that we are willing to create pg_temp if needed.
 *
 * Note: calling this may result in a CommandCounterIncrement operation,
 * if we have to create or clean out the temp namespace.
 */
Oid
LookupCreationNamespace(const char *nspname)
{
        Oid                     namespaceId;
        AclResult       aclresult;

        /* check for pg_temp alias */
        if (strcmp(nspname, "pg_temp") == 0)
        {
                /* Initialize temp namespace */
                AccessTempTableNamespace(false);
                return myTempNamespace;
        }

        namespaceId = get_namespace_oid(nspname, false);

        aclresult = pg_namespace_aclcheck(namespaceId, GetUserId(), ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
                aclcheck_error(aclresult, OBJECT_SCHEMA,
                                           nspname);

        return namespaceId;
}

/*
 * Common checks on switching namespaces.
 *
 * We complain if either the old or new namespaces is a temporary schema
 * (or temporary toast schema), or if either the old or new namespaces is the
 * TOAST schema.
 */
void
CheckSetNamespace(Oid oldNspOid, Oid nspOid)
{
        /* disallow renaming into or out of temp schemas */
        if (isAnyTempNamespace(nspOid) || isAnyTempNamespace(oldNspOid))
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("cannot move objects into or out of temporary schemas")));

        /* same for TOAST schema */
        if (nspOid == PG_TOAST_NAMESPACE || oldNspOid == PG_TOAST_NAMESPACE)
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("cannot move objects into or out of TOAST schema")));
}

/*
 * QualifiedNameGetCreationNamespace
 *              Given a possibly-qualified name for an object (in List-of-Values
 *              format), determine what namespace the object should be created in.
 *              Also extract and return the object name (last component of list).
 *
 * Note: this does not apply any permissions check.  Callers must check
 * for CREATE rights on the selected namespace when appropriate.
 *
 * Note: calling this may result in a CommandCounterIncrement operation,
 * if we have to create or clean out the temp namespace.
 */
Oid
QualifiedNameGetCreationNamespace(List *names, char **objname_p)
{
        char       *schemaname;
        Oid                     namespaceId;

        /* deconstruct the name list */
        DeconstructQualifiedName(names, &schemaname, objname_p);

        if (schemaname)
        {
                /* check for pg_temp alias */
                if (strcmp(schemaname, "pg_temp") == 0)
                {
                        /* Initialize temp namespace */
                        AccessTempTableNamespace(false);
                        return myTempNamespace;
                }
                /* use exact schema given */
                namespaceId = get_namespace_oid(schemaname, false);
                /* we do not check for USAGE rights here! */
        }
        else
        {
                /* use the default creation namespace */
                recomputeNamespacePath();
                if (activeTempCreationPending)
                {
                        /* Need to initialize temp namespace */
                        AccessTempTableNamespace(true);
                        return myTempNamespace;
                }
                namespaceId = activeCreationNamespace;
                if (!OidIsValid(namespaceId))
                        ereport(ERROR,
                                        (errcode(ERRCODE_UNDEFINED_SCHEMA),
                                         errmsg("no schema has been selected to create in")));
        }

        return namespaceId;
}

/*
 * get_namespace_oid - given a namespace name, look up the OID
 *
 * If missing_ok is false, throw an error if namespace name not found.  If
 * true, just return InvalidOid.
 */
Oid
get_namespace_oid(const char *nspname, bool missing_ok)
{
        Oid                     oid;

        oid = GetSysCacheOid1(NAMESPACENAME, Anum_pg_namespace_oid,
                                                  CStringGetDatum(nspname));
        if (!OidIsValid(oid) && !missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_SCHEMA),
                                 errmsg("schema \"%s\" does not exist", nspname)));

        return oid;
}

/*
 * makeRangeVarFromNameList
 *              Utility routine to convert a qualified-name list into RangeVar form.
 */
RangeVar *
makeRangeVarFromNameList(List *names)
{
        RangeVar   *rel = makeRangeVar(NULL, NULL, -1);

        switch (list_length(names))
        {
                case 1:
                        rel->relname = strVal(linitial(names));
                        break;
                case 2:
                        rel->schemaname = strVal(linitial(names));
                        rel->relname = strVal(lsecond(names));
                        break;
                case 3:
                        rel->catalogname = strVal(linitial(names));
                        rel->schemaname = strVal(lsecond(names));
                        rel->relname = strVal(lthird(names));
                        break;
                default:
                        ereport(ERROR,
                                        (errcode(ERRCODE_SYNTAX_ERROR),
                                         errmsg("improper relation name (too many dotted names): %s",
                                                        NameListToString(names))));
                        break;
        }

        return rel;
}

/*
 * NameListToString
 *              Utility routine to convert a qualified-name list into a string.
 *
 * This is used primarily to form error messages, and so we do not quote
 * the list elements, for the sake of legibility.
 *
 * In most scenarios the list elements should always be Value strings,
 * but we also allow A_Star for the convenience of ColumnRef processing.
 */
char *
NameListToString(List *names)
{
        StringInfoData string;
        ListCell   *l;

        initStringInfo(&string);

        foreach(l, names)
        {
                Node       *name = (Node *) lfirst(l);

                if (l != list_head(names))
                        appendStringInfoChar(&string, '.');

                if (IsA(name, String))
                        appendStringInfoString(&string, strVal(name));
                else if (IsA(name, A_Star))
                        appendStringInfoChar(&string, '*');
                else
                        elog(ERROR, "unexpected node type in name list: %d",
                                 (int) nodeTag(name));
        }

        return string.data;
}

/*
 * NameListToQuotedString
 *              Utility routine to convert a qualified-name list into a string.
 *
 * Same as above except that names will be double-quoted where necessary,
 * so the string could be re-parsed (eg, by textToQualifiedNameList).
 */
char *
NameListToQuotedString(List *names)
{
        StringInfoData string;
        ListCell   *l;

        initStringInfo(&string);

        foreach(l, names)
        {
                if (l != list_head(names))
                        appendStringInfoChar(&string, '.');
                appendStringInfoString(&string, quote_identifier(strVal(lfirst(l))));
        }

        return string.data;
}

/*
 * isTempNamespace - is the given namespace my temporary-table namespace?
 */
bool
isTempNamespace(Oid namespaceId)
{
        if (OidIsValid(myTempNamespace) && myTempNamespace == namespaceId)
                return true;
        return false;
}

/*
 * isTempToastNamespace - is the given namespace my temporary-toast-table
 *              namespace?
 */
bool
isTempToastNamespace(Oid namespaceId)
{
        if (OidIsValid(myTempToastNamespace) && myTempToastNamespace == namespaceId)
                return true;
        return false;
}

/*
 * isTempOrTempToastNamespace - is the given namespace my temporary-table
 *              namespace or my temporary-toast-table namespace?
 */
bool
isTempOrTempToastNamespace(Oid namespaceId)
{
        if (OidIsValid(myTempNamespace) &&
                (myTempNamespace == namespaceId || myTempToastNamespace == namespaceId))
                return true;
        return false;
}

/*
 * isAnyTempNamespace - is the given namespace a temporary-table namespace
 * (either my own, or another backend's)?  Temporary-toast-table namespaces
 * are included, too.
 */
bool
isAnyTempNamespace(Oid namespaceId)
{
        bool            result;
        char       *nspname;

        /* True if the namespace name starts with "pg_temp_" or "pg_toast_temp_" */
        nspname = get_namespace_name(namespaceId);
        if (!nspname)
                return false;                   /* no such namespace? */
        result = (strncmp(nspname, "pg_temp_", 8) == 0) ||
                (strncmp(nspname, "pg_toast_temp_", 14) == 0);
        pfree(nspname);
        return result;
}

/*
 * isOtherTempNamespace - is the given namespace some other backend's
 * temporary-table namespace (including temporary-toast-table namespaces)?
 *
 * Note: for most purposes in the C code, this function is obsolete.  Use
 * RELATION_IS_OTHER_TEMP() instead to detect non-local temp relations.
 */
bool
isOtherTempNamespace(Oid namespaceId)
{
        /* If it's my own temp namespace, say "false" */
        if (isTempOrTempToastNamespace(namespaceId))
                return false;
        /* Else, if it's any temp namespace, say "true" */
        return isAnyTempNamespace(namespaceId);
}

/*
 * isTempNamespaceInUse - is the given namespace owned and actively used
 * by a backend?
 *
 * Note: this can be used while scanning relations in pg_class to detect
 * orphaned temporary tables or namespaces with a backend connected to a
 * given database.  The result may be out of date quickly, so the caller
 * must be careful how to handle this information.
 */
bool
isTempNamespaceInUse(Oid namespaceId)
{
        PGPROC     *proc;
        int                     backendId;

        Assert(OidIsValid(MyDatabaseId));

        backendId = GetTempNamespaceBackendId(namespaceId);

        if (backendId == InvalidBackendId ||
                backendId == MyBackendId)
                return false;

        /* Is the backend alive? */
        proc = BackendIdGetProc(backendId);
        if (proc == NULL)
                return false;

        /* Is the backend connected to the same database we are looking at? */
        if (proc->databaseId != MyDatabaseId)
                return false;

        /* Does the backend own the temporary namespace? */
        if (proc->tempNamespaceId != namespaceId)
                return false;

        /* all good to go */
        return true;
}

/*
 * GetTempNamespaceBackendId - if the given namespace is a temporary-table
 * namespace (either my own, or another backend's), return the BackendId
 * that owns it.  Temporary-toast-table namespaces are included, too.
 * If it isn't a temp namespace, return InvalidBackendId.
 */
int
GetTempNamespaceBackendId(Oid namespaceId)
{
        int                     result;
        char       *nspname;

        /* See if the namespace name starts with "pg_temp_" or "pg_toast_temp_" */
        nspname = get_namespace_name(namespaceId);
        if (!nspname)
                return InvalidBackendId;        /* no such namespace? */
        if (strncmp(nspname, "pg_temp_", 8) == 0)
                result = atoi(nspname + 8);
        else if (strncmp(nspname, "pg_toast_temp_", 14) == 0)
                result = atoi(nspname + 14);
        else
                result = InvalidBackendId;
        pfree(nspname);
        return result;
}

/*
 * GetTempToastNamespace - get the OID of my temporary-toast-table namespace,
 * which must already be assigned.  (This is only used when creating a toast
 * table for a temp table, so we must have already done InitTempTableNamespace)
 */
Oid
GetTempToastNamespace(void)
{
        Assert(OidIsValid(myTempToastNamespace));
        return myTempToastNamespace;
}


/*
 * GetTempNamespaceState - fetch status of session's temporary namespace
 *
 * This is used for conveying state to a parallel worker, and is not meant
 * for general-purpose access.
 */
void
GetTempNamespaceState(Oid *tempNamespaceId, Oid *tempToastNamespaceId)
{
        /* Return namespace OIDs, or 0 if session has not created temp namespace */
        *tempNamespaceId = myTempNamespace;
        *tempToastNamespaceId = myTempToastNamespace;
}

/*
 * SetTempNamespaceState - set status of session's temporary namespace
 *
 * This is used for conveying state to a parallel worker, and is not meant for
 * general-purpose access.  By transferring these namespace OIDs to workers,
 * we ensure they will have the same notion of the search path as their leader
 * does.
 */
void
SetTempNamespaceState(Oid tempNamespaceId, Oid tempToastNamespaceId)
{
        /* Worker should not have created its own namespaces ... */
        Assert(myTempNamespace == InvalidOid);
        Assert(myTempToastNamespace == InvalidOid);
        Assert(myTempNamespaceSubID == InvalidSubTransactionId);

        /* Assign same namespace OIDs that leader has */
        myTempNamespace = tempNamespaceId;
        myTempToastNamespace = tempToastNamespaceId;

        /*
         * It's fine to leave myTempNamespaceSubID == InvalidSubTransactionId.
         * Even if the namespace is new so far as the leader is concerned, it's
         * not new to the worker, and we certainly wouldn't want the worker trying
         * to destroy it.
         */

        baseSearchPathValid = false;    /* may need to rebuild list */
}


/*
 * GetOverrideSearchPath - fetch current search path definition in form
 * used by PushOverrideSearchPath.
 *
 * The result structure is allocated in the specified memory context
 * (which might or might not be equal to CurrentMemoryContext); but any
 * junk created by revalidation calculations will be in CurrentMemoryContext.
 */
OverrideSearchPath *
GetOverrideSearchPath(MemoryContext context)
{
        OverrideSearchPath *result;
        List       *schemas;
        MemoryContext oldcxt;

        recomputeNamespacePath();

        oldcxt = MemoryContextSwitchTo(context);

        result = (OverrideSearchPath *) palloc0(sizeof(OverrideSearchPath));
        schemas = list_copy(activeSearchPath);
        while (schemas && linitial_oid(schemas) != activeCreationNamespace)
        {
                if (linitial_oid(schemas) == myTempNamespace)
                        result->addTemp = true;
                else
                {
                        Assert(linitial_oid(schemas) == PG_CATALOG_NAMESPACE);
                        result->addCatalog = true;
                }
                schemas = list_delete_first(schemas);
        }
        result->schemas = schemas;

        MemoryContextSwitchTo(oldcxt);

        return result;
}

/*
 * CopyOverrideSearchPath - copy the specified OverrideSearchPath.
 *
 * The result structure is allocated in CurrentMemoryContext.
 */
OverrideSearchPath *
CopyOverrideSearchPath(OverrideSearchPath *path)
{
        OverrideSearchPath *result;

        result = (OverrideSearchPath *) palloc(sizeof(OverrideSearchPath));
        result->schemas = list_copy(path->schemas);
        result->addCatalog = path->addCatalog;
        result->addTemp = path->addTemp;

        return result;
}

/*
 * OverrideSearchPathMatchesCurrent - does path match current setting?
 */
bool
OverrideSearchPathMatchesCurrent(OverrideSearchPath *path)
{
        ListCell   *lc,
                           *lcp;

        recomputeNamespacePath();

        /* We scan down the activeSearchPath to see if it matches the input. */
        lc = list_head(activeSearchPath);

        /* If path->addTemp, first item should be my temp namespace. */
        if (path->addTemp)
        {
                if (lc && lfirst_oid(lc) == myTempNamespace)
                        lc = lnext(lc);
                else
                        return false;
        }
        /* If path->addCatalog, next item should be pg_catalog. */
        if (path->addCatalog)
        {
                if (lc && lfirst_oid(lc) == PG_CATALOG_NAMESPACE)
                        lc = lnext(lc);
                else
                        return false;
        }
        /* We should now be looking at the activeCreationNamespace. */
        if (activeCreationNamespace != (lc ? lfirst_oid(lc) : InvalidOid))
                return false;
        /* The remainder of activeSearchPath should match path->schemas. */
        foreach(lcp, path->schemas)
        {
                if (lc && lfirst_oid(lc) == lfirst_oid(lcp))
                        lc = lnext(lc);
                else
                        return false;
        }
        if (lc)
                return false;
        return true;
}

/*
 * PushOverrideSearchPath - temporarily override the search path
 *
 * We allow nested overrides, hence the push/pop terminology.  The GUC
 * search_path variable is ignored while an override is active.
 *
 * It's possible that newpath->useTemp is set but there is no longer any
 * active temp namespace, if the path was saved during a transaction that
 * created a temp namespace and was later rolled back.  In that case we just
 * ignore useTemp.  A plausible alternative would be to create a new temp
 * namespace, but for existing callers that's not necessary because an empty
 * temp namespace wouldn't affect their results anyway.
 *
 * It's also worth noting that other schemas listed in newpath might not
 * exist anymore either.  We don't worry about this because OIDs that match
 * no existing namespace will simply not produce any hits during searches.
 */
void
PushOverrideSearchPath(OverrideSearchPath *newpath)
{
        OverrideStackEntry *entry;
        List       *oidlist;
        Oid                     firstNS;
        MemoryContext oldcxt;

        /*
         * Copy the list for safekeeping, and insert implicitly-searched
         * namespaces as needed.  This code should track recomputeNamespacePath.
         */
        oldcxt = MemoryContextSwitchTo(TopMemoryContext);

        oidlist = list_copy(newpath->schemas);

        /*
         * Remember the first member of the explicit list.
         */
        if (oidlist == NIL)
                firstNS = InvalidOid;
        else
                firstNS = linitial_oid(oidlist);

        /*
         * Add any implicitly-searched namespaces to the list.  Note these go on
         * the front, not the back; also notice that we do not check USAGE
         * permissions for these.
         */
        if (newpath->addCatalog)
                oidlist = lcons_oid(PG_CATALOG_NAMESPACE, oidlist);

        if (newpath->addTemp && OidIsValid(myTempNamespace))
                oidlist = lcons_oid(myTempNamespace, oidlist);

        /*
         * Build the new stack entry, then insert it at the head of the list.
         */
        entry = (OverrideStackEntry *) palloc(sizeof(OverrideStackEntry));
        entry->searchPath = oidlist;
        entry->creationNamespace = firstNS;
        entry->nestLevel = GetCurrentTransactionNestLevel();

        overrideStack = lcons(entry, overrideStack);

        /* And make it active. */
        activeSearchPath = entry->searchPath;
        activeCreationNamespace = entry->creationNamespace;
        activeTempCreationPending = false;      /* XXX is this OK? */

        MemoryContextSwitchTo(oldcxt);
}

/*
 * PopOverrideSearchPath - undo a previous PushOverrideSearchPath
 *
 * Any push during a (sub)transaction will be popped automatically at abort.
 * But it's caller error if a push isn't popped in normal control flow.
 */
void
PopOverrideSearchPath(void)
{
        OverrideStackEntry *entry;

        /* Sanity checks. */
        if (overrideStack == NIL)
                elog(ERROR, "bogus PopOverrideSearchPath call");
        entry = (OverrideStackEntry *) linitial(overrideStack);
        if (entry->nestLevel != GetCurrentTransactionNestLevel())
                elog(ERROR, "bogus PopOverrideSearchPath call");

        /* Pop the stack and free storage. */
        overrideStack = list_delete_first(overrideStack);
        list_free(entry->searchPath);
        pfree(entry);

        /* Activate the next level down. */
        if (overrideStack)
        {
                entry = (OverrideStackEntry *) linitial(overrideStack);
                activeSearchPath = entry->searchPath;
                activeCreationNamespace = entry->creationNamespace;
                activeTempCreationPending = false;      /* XXX is this OK? */
        }
        else
        {
                /* If not baseSearchPathValid, this is useless but harmless */
                activeSearchPath = baseSearchPath;
                activeCreationNamespace = baseCreationNamespace;
                activeTempCreationPending = baseTempCreationPending;
        }
}


/*
 * get_collation_oid - find a collation by possibly qualified name
 *
 * Note that this will only find collations that work with the current
 * database's encoding.
 */
Oid
get_collation_oid(List *name, bool missing_ok)
{
        char       *schemaname;
        char       *collation_name;
        int32           dbencoding = GetDatabaseEncoding();
        Oid                     namespaceId;
        Oid                     colloid;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(name, &schemaname, &collation_name);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (missing_ok && !OidIsValid(namespaceId))
                        return InvalidOid;

                colloid = lookup_collation(collation_name, namespaceId, dbencoding);
                if (OidIsValid(colloid))
                        return colloid;
        }
        else
        {
                /* search for it in search path */
                recomputeNamespacePath();

                foreach(l, activeSearchPath)
                {
                        namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        colloid = lookup_collation(collation_name, namespaceId, dbencoding);
                        if (OidIsValid(colloid))
                                return colloid;
                }
        }

        /* Not found in path */
        if (!missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("collation \"%s\" for encoding \"%s\" does not exist",
                                                NameListToString(name), GetDatabaseEncodingName())));
        return InvalidOid;
}

/*
 * get_conversion_oid - find a conversion by possibly qualified name
 */
Oid
get_conversion_oid(List *name, bool missing_ok)
{
        char       *schemaname;
        char       *conversion_name;
        Oid                     namespaceId;
        Oid                     conoid = InvalidOid;
        ListCell   *l;

        /* deconstruct the name list */
        DeconstructQualifiedName(name, &schemaname, &conversion_name);

        if (schemaname)
        {
                /* use exact schema given */
                namespaceId = LookupExplicitNamespace(schemaname, missing_ok);
                if (missing_ok && !OidIsValid(namespaceId))
                        conoid = InvalidOid;
                else
                        conoid = GetSysCacheOid2(CONNAMENSP, Anum_pg_conversion_oid,
                                                                         PointerGetDatum(conversion_name),
                                                                         ObjectIdGetDatum(namespaceId));
        }
        else
        {
                /* search for it in search path */
                recomputeNamespacePath();

                foreach(l, activeSearchPath)
                {
                        namespaceId = lfirst_oid(l);

                        if (namespaceId == myTempNamespace)
                                continue;               /* do not look in temp namespace */

                        conoid = GetSysCacheOid2(CONNAMENSP, Anum_pg_conversion_oid,
                                                                         PointerGetDatum(conversion_name),
                                                                         ObjectIdGetDatum(namespaceId));
                        if (OidIsValid(conoid))
                                return conoid;
                }
        }

        /* Not found in path */
        if (!OidIsValid(conoid) && !missing_ok)
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_OBJECT),
                                 errmsg("conversion \"%s\" does not exist",
                                                NameListToString(name))));
        return conoid;
}

/*
 * FindDefaultConversionProc - find default encoding conversion proc
 */
Oid
FindDefaultConversionProc(int32 for_encoding, int32 to_encoding)
{
        Oid                     proc;
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);

                if (namespaceId == myTempNamespace)
                        continue;                       /* do not look in temp namespace */

                proc = FindDefaultConversion(namespaceId, for_encoding, to_encoding);
                if (OidIsValid(proc))
                        return proc;
        }

        /* Not found in path */
        return InvalidOid;
}

/*
 * recomputeNamespacePath - recompute path derived variables if needed.
 */
static void
recomputeNamespacePath(void)
{
        Oid                     roleid = GetUserId();
        char       *rawname;
        List       *namelist;
        List       *oidlist;
        List       *newpath;
        ListCell   *l;
        bool            temp_missing;
        Oid                     firstNS;
        MemoryContext oldcxt;

        /* Do nothing if an override search spec is active. */
        if (overrideStack)
                return;

        /* Do nothing if path is already valid. */
        if (baseSearchPathValid && namespaceUser == roleid)
                return;

        /* Need a modifiable copy of namespace_search_path string */
        rawname = pstrdup(namespace_search_path);

        /* Parse string into list of identifiers */
        if (!SplitIdentifierString(rawname, ',', &namelist))
        {
                /* syntax error in name list */
                /* this should not happen if GUC checked check_search_path */
                elog(ERROR, "invalid list syntax");
        }

        /*
         * Convert the list of names to a list of OIDs.  If any names are not
         * recognizable or we don't have read access, just leave them out of the
         * list.  (We can't raise an error, since the search_path setting has
         * already been accepted.)      Don't make duplicate entries, either.
         */
        oidlist = NIL;
        temp_missing = false;
        foreach(l, namelist)
        {
                char       *curname = (char *) lfirst(l);
                Oid                     namespaceId;

                if (strcmp(curname, "$user") == 0)
                {
                        /* $user --- substitute namespace matching user name, if any */
                        HeapTuple       tuple;

                        tuple = SearchSysCache1(AUTHOID, ObjectIdGetDatum(roleid));
                        if (HeapTupleIsValid(tuple))
                        {
                                char       *rname;

                                rname = NameStr(((Form_pg_authid) GETSTRUCT(tuple))->rolname);
                                namespaceId = get_namespace_oid(rname, true);
                                ReleaseSysCache(tuple);
                                if (OidIsValid(namespaceId) &&
                                        !list_member_oid(oidlist, namespaceId) &&
                                        pg_namespace_aclcheck(namespaceId, roleid,
                                                                                  ACL_USAGE) == ACLCHECK_OK &&
                                        InvokeNamespaceSearchHook(namespaceId, false))
                                        oidlist = lappend_oid(oidlist, namespaceId);
                        }
                }
                else if (strcmp(curname, "pg_temp") == 0)
                {
                        /* pg_temp --- substitute temp namespace, if any */
                        if (OidIsValid(myTempNamespace))
                        {
                                if (!list_member_oid(oidlist, myTempNamespace) &&
                                        InvokeNamespaceSearchHook(myTempNamespace, false))
                                        oidlist = lappend_oid(oidlist, myTempNamespace);
                        }
                        else
                        {
                                /* If it ought to be the creation namespace, set flag */
                                if (oidlist == NIL)
                                        temp_missing = true;
                        }
                }
                else
                {
                        /* normal namespace reference */
                        namespaceId = get_namespace_oid(curname, true);
                        if (OidIsValid(namespaceId) &&
                                !list_member_oid(oidlist, namespaceId) &&
                                pg_namespace_aclcheck(namespaceId, roleid,
                                                                          ACL_USAGE) == ACLCHECK_OK &&
                                InvokeNamespaceSearchHook(namespaceId, false))
                                oidlist = lappend_oid(oidlist, namespaceId);
                }
        }

        /*
         * Remember the first member of the explicit list.  (Note: this is
         * nominally wrong if temp_missing, but we need it anyway to distinguish
         * explicit from implicit mention of pg_catalog.)
         */
        if (oidlist == NIL)
                firstNS = InvalidOid;
        else
                firstNS = linitial_oid(oidlist);

        /*
         * Add any implicitly-searched namespaces to the list.  Note these go on
         * the front, not the back; also notice that we do not check USAGE
         * permissions for these.
         */
        if (!list_member_oid(oidlist, PG_CATALOG_NAMESPACE))
                oidlist = lcons_oid(PG_CATALOG_NAMESPACE, oidlist);

        if (OidIsValid(myTempNamespace) &&
                !list_member_oid(oidlist, myTempNamespace))
                oidlist = lcons_oid(myTempNamespace, oidlist);

        /*
         * Now that we've successfully built the new list of namespace OIDs, save
         * it in permanent storage.
         */
        oldcxt = MemoryContextSwitchTo(TopMemoryContext);
        newpath = list_copy(oidlist);
        MemoryContextSwitchTo(oldcxt);

        /* Now safe to assign to state variables. */
        list_free(baseSearchPath);
        baseSearchPath = newpath;
        baseCreationNamespace = firstNS;
        baseTempCreationPending = temp_missing;

        /* Mark the path valid. */
        baseSearchPathValid = true;
        namespaceUser = roleid;

        /* And make it active. */
        activeSearchPath = baseSearchPath;
        activeCreationNamespace = baseCreationNamespace;
        activeTempCreationPending = baseTempCreationPending;

        /* Clean up. */
        pfree(rawname);
        list_free(namelist);
        list_free(oidlist);
}

/*
 * AccessTempTableNamespace
 *              Provide access to a temporary namespace, potentially creating it
 *              if not present yet.  This routine registers if the namespace gets
 *              in use in this transaction.  'force' can be set to true to allow
 *              the caller to enforce the creation of the temporary namespace for
 *              use in this backend, which happens if its creation is pending.
 */
static void
AccessTempTableNamespace(bool force)
{
        /*
         * Make note that this temporary namespace has been accessed in this
         * transaction.
         */
        MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;

        /*
         * If the caller attempting to access a temporary schema expects the
         * creation of the namespace to be pending and should be enforced, then go
         * through the creation.
         */
        if (!force && OidIsValid(myTempNamespace))
                return;

        /*
         * The temporary tablespace does not exist yet and is wanted, so
         * initialize it.
         */
        InitTempTableNamespace();
}

/*
 * InitTempTableNamespace
 *              Initialize temp table namespace on first use in a particular backend
 */
static void
InitTempTableNamespace(void)
{
        char            namespaceName[NAMEDATALEN];
        Oid                     namespaceId;
        Oid                     toastspaceId;

        Assert(!OidIsValid(myTempNamespace));

        /*
         * First, do permission check to see if we are authorized to make temp
         * tables.  We use a nonstandard error message here since "databasename:
         * permission denied" might be a tad cryptic.
         *
         * Note that ACL_CREATE_TEMP rights are rechecked in pg_namespace_aclmask;
         * that's necessary since current user ID could change during the session.
         * But there's no need to make the namespace in the first place until a
         * temp table creation request is made by someone with appropriate rights.
         */
        if (pg_database_aclcheck(MyDatabaseId, GetUserId(),
                                                         ACL_CREATE_TEMP) != ACLCHECK_OK)
                ereport(ERROR,
                                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                                 errmsg("permission denied to create temporary tables in database \"%s\"",
                                                get_database_name(MyDatabaseId))));

        /*
         * Do not allow a Hot Standby session to make temp tables.  Aside from
         * problems with modifying the system catalogs, there is a naming
         * conflict: pg_temp_N belongs to the session with BackendId N on the
         * master, not to a hot standby session with the same BackendId.  We
         * should not be able to get here anyway due to XactReadOnly checks, but
         * let's just make real sure.  Note that this also backstops various
         * operations that allow XactReadOnly transactions to modify temp tables;
         * they'd need RecoveryInProgress checks if not for this.
         */
        if (RecoveryInProgress())
                ereport(ERROR,
                                (errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
                                 errmsg("cannot create temporary tables during recovery")));

        /* Parallel workers can't create temporary tables, either. */
        if (IsParallelWorker())
                ereport(ERROR,
                                (errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
                                 errmsg("cannot create temporary tables during a parallel operation")));

        snprintf(namespaceName, sizeof(namespaceName), "pg_temp_%d", MyBackendId);

        namespaceId = get_namespace_oid(namespaceName, true);
        if (!OidIsValid(namespaceId))
        {
                /*
                 * First use of this temp namespace in this database; create it. The
                 * temp namespaces are always owned by the superuser.  We leave their
                 * permissions at default --- i.e., no access except to superuser ---
                 * to ensure that unprivileged users can't peek at other backends'
                 * temp tables.  This works because the places that access the temp
                 * namespace for my own backend skip permissions checks on it.
                 */
                namespaceId = NamespaceCreate(namespaceName, BOOTSTRAP_SUPERUSERID,
                                                                          true);
                /* Advance command counter to make namespace visible */
                CommandCounterIncrement();
        }
        else
        {
                /*
                 * If the namespace already exists, clean it out (in case the former
                 * owner crashed without doing so).
                 */
                RemoveTempRelations(namespaceId);
        }

        /*
         * If the corresponding toast-table namespace doesn't exist yet, create
         * it. (We assume there is no need to clean it out if it does exist, since
         * dropping a parent table should make its toast table go away.)
         */
        snprintf(namespaceName, sizeof(namespaceName), "pg_toast_temp_%d",
                         MyBackendId);

        toastspaceId = get_namespace_oid(namespaceName, true);
        if (!OidIsValid(toastspaceId))
        {
                toastspaceId = NamespaceCreate(namespaceName, BOOTSTRAP_SUPERUSERID,
                                                                           true);
                /* Advance command counter to make namespace visible */
                CommandCounterIncrement();
        }

        /*
         * Okay, we've prepared the temp namespace ... but it's not committed yet,
         * so all our work could be undone by transaction rollback.  Set flag for
         * AtEOXact_Namespace to know what to do.
         */
        myTempNamespace = namespaceId;
        myTempToastNamespace = toastspaceId;

        /*
         * Mark MyProc as owning this namespace which other processes can use to
         * decide if a temporary namespace is in use or not.  We assume that
         * assignment of namespaceId is an atomic operation.  Even if it is not,
         * the temporary relation which resulted in the creation of this temporary
         * namespace is still locked until the current transaction commits, and
         * its pg_namespace row is not visible yet.  However it does not matter:
         * this flag makes the namespace as being in use, so no objects created on
         * it would be removed concurrently.
         */
        MyProc->tempNamespaceId = namespaceId;

        /* It should not be done already. */
        AssertState(myTempNamespaceSubID == InvalidSubTransactionId);
        myTempNamespaceSubID = GetCurrentSubTransactionId();

        baseSearchPathValid = false;    /* need to rebuild list */
}

/*
 * End-of-transaction cleanup for namespaces.
 */
void
AtEOXact_Namespace(bool isCommit, bool parallel)
{
        /*
         * If we abort the transaction in which a temp namespace was selected,
         * we'll have to do any creation or cleanout work over again.  So, just
         * forget the namespace entirely until next time.  On the other hand, if
         * we commit then register an exit callback to clean out the temp tables
         * at backend shutdown.  (We only want to register the callback once per
         * session, so this is a good place to do it.)
         */
        if (myTempNamespaceSubID != InvalidSubTransactionId && !parallel)
        {
                if (isCommit)
                        before_shmem_exit(RemoveTempRelationsCallback, 0);
                else
                {
                        myTempNamespace = InvalidOid;
                        myTempToastNamespace = InvalidOid;
                        baseSearchPathValid = false;    /* need to rebuild list */

                        /*
                         * Reset the temporary namespace flag in MyProc.  We assume that
                         * this operation is atomic.
                         *
                         * Because this transaction is aborting, the pg_namespace row is
                         * not visible to anyone else anyway, but that doesn't matter:
                         * it's not a problem if objects contained in this namespace are
                         * removed concurrently.
                         */
                        MyProc->tempNamespaceId = InvalidOid;
                }
                myTempNamespaceSubID = InvalidSubTransactionId;
        }

        /*
         * Clean up if someone failed to do PopOverrideSearchPath
         */
        if (overrideStack)
        {
                if (isCommit)
                        elog(WARNING, "leaked override search path");
                while (overrideStack)
                {
                        OverrideStackEntry *entry;

                        entry = (OverrideStackEntry *) linitial(overrideStack);
                        overrideStack = list_delete_first(overrideStack);
                        list_free(entry->searchPath);
                        pfree(entry);
                }
                /* If not baseSearchPathValid, this is useless but harmless */
                activeSearchPath = baseSearchPath;
                activeCreationNamespace = baseCreationNamespace;
                activeTempCreationPending = baseTempCreationPending;
        }
}

/*
 * AtEOSubXact_Namespace
 *
 * At subtransaction commit, propagate the temp-namespace-creation
 * flag to the parent subtransaction.
 *
 * At subtransaction abort, forget the flag if we set it up.
 */
void
AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
                                          SubTransactionId parentSubid)
{
        OverrideStackEntry *entry;

        if (myTempNamespaceSubID == mySubid)
        {
                if (isCommit)
                        myTempNamespaceSubID = parentSubid;
                else
                {
                        myTempNamespaceSubID = InvalidSubTransactionId;
                        /* TEMP namespace creation failed, so reset state */
                        myTempNamespace = InvalidOid;
                        myTempToastNamespace = InvalidOid;
                        baseSearchPathValid = false;    /* need to rebuild list */

                        /*
                         * Reset the temporary namespace flag in MyProc.  We assume that
                         * this operation is atomic.
                         *
                         * Because this subtransaction is aborting, the pg_namespace row
                         * is not visible to anyone else anyway, but that doesn't matter:
                         * it's not a problem if objects contained in this namespace are
                         * removed concurrently.
                         */
                        MyProc->tempNamespaceId = InvalidOid;
                }
        }

        /*
         * Clean up if someone failed to do PopOverrideSearchPath
         */
        while (overrideStack)
        {
                entry = (OverrideStackEntry *) linitial(overrideStack);
                if (entry->nestLevel < GetCurrentTransactionNestLevel())
                        break;
                if (isCommit)
                        elog(WARNING, "leaked override search path");
                overrideStack = list_delete_first(overrideStack);
                list_free(entry->searchPath);
                pfree(entry);
        }

        /* Activate the next level down. */
        if (overrideStack)
        {
                entry = (OverrideStackEntry *) linitial(overrideStack);
                activeSearchPath = entry->searchPath;
                activeCreationNamespace = entry->creationNamespace;
                activeTempCreationPending = false;      /* XXX is this OK? */
        }
        else
        {
                /* If not baseSearchPathValid, this is useless but harmless */
                activeSearchPath = baseSearchPath;
                activeCreationNamespace = baseCreationNamespace;
                activeTempCreationPending = baseTempCreationPending;
        }
}

/*
 * Remove all relations in the specified temp namespace.
 *
 * This is called at backend shutdown (if we made any temp relations).
 * It is also called when we begin using a pre-existing temp namespace,
 * in order to clean out any relations that might have been created by
 * a crashed backend.
 */
static void
RemoveTempRelations(Oid tempNamespaceId)
{
        ObjectAddress object;

        /*
         * We want to get rid of everything in the target namespace, but not the
         * namespace itself (deleting it only to recreate it later would be a
         * waste of cycles).  Hence, specify SKIP_ORIGINAL.  It's also an INTERNAL
         * deletion, and we want to not drop any extensions that might happen to
         * own temp objects.
         */
        object.classId = NamespaceRelationId;
        object.objectId = tempNamespaceId;
        object.objectSubId = 0;

        performDeletion(&object, DROP_CASCADE,
                                        PERFORM_DELETION_INTERNAL |
                                        PERFORM_DELETION_QUIETLY |
                                        PERFORM_DELETION_SKIP_ORIGINAL |
                                        PERFORM_DELETION_SKIP_EXTENSIONS);
}

/*
 * Callback to remove temp relations at backend exit.
 */
static void
RemoveTempRelationsCallback(int code, Datum arg)
{
        if (OidIsValid(myTempNamespace))        /* should always be true */
        {
                /* Need to ensure we have a usable transaction. */
                AbortOutOfAnyTransaction();
                StartTransactionCommand();

                RemoveTempRelations(myTempNamespace);

                CommitTransactionCommand();
        }
}

/*
 * Remove all temp tables from the temporary namespace.
 */
void
ResetTempTableNamespace(void)
{
        if (OidIsValid(myTempNamespace))
                RemoveTempRelations(myTempNamespace);
}


/*
 * Routines for handling the GUC variable 'search_path'.
 */

/* check_hook: validate new search_path value */
bool
check_search_path(char **newval, void **extra, GucSource source)
{
        char       *rawname;
        List       *namelist;

        /* Need a modifiable copy of string */
        rawname = pstrdup(*newval);

        /* Parse string into list of identifiers */
        if (!SplitIdentifierString(rawname, ',', &namelist))
        {
                /* syntax error in name list */
                GUC_check_errdetail("List syntax is invalid.");
                pfree(rawname);
                list_free(namelist);
                return false;
        }

        /*
         * We used to try to check that the named schemas exist, but there are
         * many valid use-cases for having search_path settings that include
         * schemas that don't exist; and often, we are not inside a transaction
         * here and so can't consult the system catalogs anyway.  So now, the only
         * requirement is syntactic validity of the identifier list.
         */

        pfree(rawname);
        list_free(namelist);

        return true;
}

/* assign_hook: do extra actions as needed */
void
assign_search_path(const char *newval, void *extra)
{
        /*
         * We mark the path as needing recomputation, but don't do anything until
         * it's needed.  This avoids trying to do database access during GUC
         * initialization, or outside a transaction.
         */
        baseSearchPathValid = false;
}

/*
 * InitializeSearchPath: initialize module during InitPostgres.
 *
 * This is called after we are up enough to be able to do catalog lookups.
 */
void
InitializeSearchPath(void)
{
        if (IsBootstrapProcessingMode())
        {
                /*
                 * In bootstrap mode, the search path must be 'pg_catalog' so that
                 * tables are created in the proper namespace; ignore the GUC setting.
                 */
                MemoryContext oldcxt;

                oldcxt = MemoryContextSwitchTo(TopMemoryContext);
                baseSearchPath = list_make1_oid(PG_CATALOG_NAMESPACE);
                MemoryContextSwitchTo(oldcxt);
                baseCreationNamespace = PG_CATALOG_NAMESPACE;
                baseTempCreationPending = false;
                baseSearchPathValid = true;
                namespaceUser = GetUserId();
                activeSearchPath = baseSearchPath;
                activeCreationNamespace = baseCreationNamespace;
                activeTempCreationPending = baseTempCreationPending;
        }
        else
        {
                /*
                 * In normal mode, arrange for a callback on any syscache invalidation
                 * of pg_namespace rows.
                 */
                CacheRegisterSyscacheCallback(NAMESPACEOID,
                                                                          NamespaceCallback,
                                                                          (Datum) 0);
                /* Force search path to be recomputed on next use */
                baseSearchPathValid = false;
        }
}

/*
 * NamespaceCallback
 *              Syscache inval callback function
 */
static void
NamespaceCallback(Datum arg, int cacheid, uint32 hashvalue)
{
        /* Force search path to be recomputed on next use */
        baseSearchPathValid = false;
}

/*
 * Fetch the active search path. The return value is a palloc'ed list
 * of OIDs; the caller is responsible for freeing this storage as
 * appropriate.
 *
 * The returned list includes the implicitly-prepended namespaces only if
 * includeImplicit is true.
 *
 * Note: calling this may result in a CommandCounterIncrement operation,
 * if we have to create or clean out the temp namespace.
 */
List *
fetch_search_path(bool includeImplicit)
{
        List       *result;

        recomputeNamespacePath();

        /*
         * If the temp namespace should be first, force it to exist.  This is so
         * that callers can trust the result to reflect the actual default
         * creation namespace.  It's a bit bogus to do this here, since
         * current_schema() is supposedly a stable function without side-effects,
         * but the alternatives seem worse.
         */
        if (activeTempCreationPending)
        {
                AccessTempTableNamespace(true);
                recomputeNamespacePath();
        }

        result = list_copy(activeSearchPath);
        if (!includeImplicit)
        {
                while (result && linitial_oid(result) != activeCreationNamespace)
                        result = list_delete_first(result);
        }

        return result;
}

/*
 * Fetch the active search path into a caller-allocated array of OIDs.
 * Returns the number of path entries.  (If this is more than sarray_len,
 * then the data didn't fit and is not all stored.)
 *
 * The returned list always includes the implicitly-prepended namespaces,
 * but never includes the temp namespace.  (This is suitable for existing
 * users, which would want to ignore the temp namespace anyway.)  This
 * definition allows us to not worry about initializing the temp namespace.
 */
int
fetch_search_path_array(Oid *sarray, int sarray_len)
{
        int                     count = 0;
        ListCell   *l;

        recomputeNamespacePath();

        foreach(l, activeSearchPath)
        {
                Oid                     namespaceId = lfirst_oid(l);

                if (namespaceId == myTempNamespace)
                        continue;                       /* do not include temp namespace */

                if (count < sarray_len)
                        sarray[count] = namespaceId;
                count++;
        }

        return count;
}


/*
 * Export the FooIsVisible functions as SQL-callable functions.
 *
 * Note: as of Postgres 8.4, these will silently return NULL if called on
 * a nonexistent object OID, rather than failing.  This is to avoid race
 * condition errors when a query that's scanning a catalog using an MVCC
 * snapshot uses one of these functions.  The underlying IsVisible functions
 * always use an up-to-date snapshot and so might see the object as already
 * gone when it's still visible to the transaction snapshot.  (There is no race
 * condition in the current coding because we don't accept sinval messages
 * between the SearchSysCacheExists test and the subsequent lookup.)
 */

Datum
pg_table_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(RelationIsVisible(oid));
}

Datum
pg_type_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(TYPEOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(TypeIsVisible(oid));
}

Datum
pg_function_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(PROCOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(FunctionIsVisible(oid));
}

Datum
pg_operator_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(OPEROID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(OperatorIsVisible(oid));
}

Datum
pg_opclass_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(CLAOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(OpclassIsVisible(oid));
}

Datum
pg_opfamily_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(OPFAMILYOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(OpfamilyIsVisible(oid));
}

Datum
pg_collation_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(COLLOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(CollationIsVisible(oid));
}

Datum
pg_conversion_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(CONVOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(ConversionIsVisible(oid));
}

Datum
pg_statistics_obj_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(STATEXTOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(StatisticsObjIsVisible(oid));
}

Datum
pg_ts_parser_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(TSPARSEROID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(TSParserIsVisible(oid));
}

Datum
pg_ts_dict_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(TSDICTOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(TSDictionaryIsVisible(oid));
}

Datum
pg_ts_template_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(TSTEMPLATEOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(TSTemplateIsVisible(oid));
}

Datum
pg_ts_config_is_visible(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        if (!SearchSysCacheExists1(TSCONFIGOID, ObjectIdGetDatum(oid)))
                PG_RETURN_NULL();

        PG_RETURN_BOOL(TSConfigIsVisible(oid));
}

Datum
pg_my_temp_schema(PG_FUNCTION_ARGS)
{
        PG_RETURN_OID(myTempNamespace);
}

Datum
pg_is_other_temp_schema(PG_FUNCTION_ARGS)
{
        Oid                     oid = PG_GETARG_OID(0);

        PG_RETURN_BOOL(isOtherTempNamespace(oid));
}