[postgresql] / src / backend / rewrite / rewriteHandler.c

/*-------------------------------------------------------------------------
 *
 * rewriteHandler.c
 *              Primary module of query rewriter.
 *
 * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.122 2003/07/03 16:34:25 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/prep.h"
#include "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parse_type.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"


/* We use a list of these to detect recursion in RewriteQuery */
typedef struct rewrite_event {
        Oid                     relation;               /* OID of relation having rules */
        CmdType         event;                  /* type of rule being fired */
} rewrite_event;

static Query *rewriteRuleAction(Query *parsetree,
                                  Query *rule_action,
                                  Node *rule_qual,
                                  int rt_index,
                                  CmdType event);
static List *adjustJoinTreeList(Query *parsetree, bool removert, int rt_index);
static void rewriteTargetList(Query *parsetree, Relation target_relation);
static TargetEntry *process_matched_tle(TargetEntry *src_tle,
                                        TargetEntry *prior_tle);
static void markQueryForUpdate(Query *qry, bool skipOldNew);
static List *matchLocks(CmdType event, RuleLock *rulelocks,
                   int varno, Query *parsetree);
static Query *fireRIRrules(Query *parsetree, List *activeRIRs);


/*
 * rewriteRuleAction -
 *        Rewrite the rule action with appropriate qualifiers (taken from
 *        the triggering query).
 */
static Query *
rewriteRuleAction(Query *parsetree,
                                  Query *rule_action,
                                  Node *rule_qual,
                                  int rt_index,
                                  CmdType event)
{
        int                     current_varno,
                                new_varno;
        List       *main_rtable;
        int                     rt_length;
        Query      *sub_action;
        Query     **sub_action_ptr;
        List       *rt;

        /*
         * Make modifiable copies of rule action and qual (what we're passed
         * are the stored versions in the relcache; don't touch 'em!).
         */
        rule_action = (Query *) copyObject(rule_action);
        rule_qual = (Node *) copyObject(rule_qual);

        current_varno = rt_index;
        rt_length = length(parsetree->rtable);
        new_varno = PRS2_NEW_VARNO + rt_length;

        /*
         * Adjust rule action and qual to offset its varnos, so that we can
         * merge its rtable with the main parsetree's rtable.
         *
         * If the rule action is an INSERT...SELECT, the OLD/NEW rtable entries
         * will be in the SELECT part, and we have to modify that rather than
         * the top-level INSERT (kluge!).
         */
        sub_action = getInsertSelectQuery(rule_action, &sub_action_ptr);

        OffsetVarNodes((Node *) sub_action, rt_length, 0);
        OffsetVarNodes(rule_qual, rt_length, 0);
        /* but references to *OLD* should point at original rt_index */
        ChangeVarNodes((Node *) sub_action,
                                   PRS2_OLD_VARNO + rt_length, rt_index, 0);
        ChangeVarNodes(rule_qual,
                                   PRS2_OLD_VARNO + rt_length, rt_index, 0);

        /*
         * Generate expanded rtable consisting of main parsetree's rtable plus
         * rule action's rtable; this becomes the complete rtable for the rule
         * action.      Some of the entries may be unused after we finish
         * rewriting, but if we tried to remove them we'd have a much
         * harder job to adjust RT indexes in the query's Vars.  It's OK to
         * have unused RT entries, since planner will ignore them.
         *
         * NOTE: because planner will destructively alter rtable, we must ensure
         * that rule action's rtable is separate and shares no substructure
         * with the main rtable.  Hence do a deep copy here.
         *
         * Also, we must disable write-access checking in all the RT entries
         * copied from the main query.  This is safe since in fact the rule action
         * won't write on them, and it's necessary because the rule action may
         * have a different commandType than the main query, causing
         * ExecCheckRTEPerms() to make an inappropriate check.  The read-access
         * checks can be left enabled, although they're probably redundant.
         */
        main_rtable = (List *) copyObject(parsetree->rtable);

        foreach(rt, main_rtable)
        {
                RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);

                rte->checkForWrite = false;
        }

        sub_action->rtable = nconc(main_rtable, sub_action->rtable);

        /*
         * Each rule action's jointree should be the main parsetree's jointree
         * plus that rule's jointree, but usually *without* the original
         * rtindex that we're replacing (if present, which it won't be for
         * INSERT). Note that if the rule action refers to OLD, its jointree
         * will add a reference to rt_index.  If the rule action doesn't refer
         * to OLD, but either the rule_qual or the user query quals do, then
         * we need to keep the original rtindex in the jointree to provide
         * data for the quals.  We don't want the original rtindex to be
         * joined twice, however, so avoid keeping it if the rule action
         * mentions it.
         *
         * As above, the action's jointree must not share substructure with the
         * main parsetree's.
         */
        if (sub_action->jointree != NULL)
        {
                bool            keeporig;
                List       *newjointree;

                keeporig = (!rangeTableEntry_used((Node *) sub_action->jointree,
                                                                                  rt_index, 0)) &&
                        (rangeTableEntry_used(rule_qual, rt_index, 0) ||
                  rangeTableEntry_used(parsetree->jointree->quals, rt_index, 0));
                newjointree = adjustJoinTreeList(parsetree, !keeporig, rt_index);
                sub_action->jointree->fromlist =
                        nconc(newjointree, sub_action->jointree->fromlist);
        }

        /*
         * We copy the qualifications of the parsetree to the action and vice
         * versa. So force hasSubLinks if one of them has it. If this is not
         * right, the flag will get cleared later, but we mustn't risk having
         * it not set when it needs to be.      (XXX this should probably be
         * handled by AddQual and friends, not here...)
         */
        if (parsetree->hasSubLinks)
                sub_action->hasSubLinks = TRUE;
        else if (sub_action->hasSubLinks)
                parsetree->hasSubLinks = TRUE;

        /*
         * Event Qualification forces copying of parsetree and splitting into
         * two queries one w/rule_qual, one w/NOT rule_qual. Also add user
         * query qual onto rule action
         */
        AddQual(sub_action, rule_qual);

        AddQual(sub_action, parsetree->jointree->quals);

        /*
         * Rewrite new.attribute w/ right hand side of target-list entry for
         * appropriate field name in insert/update.
         *
         * KLUGE ALERT: since ResolveNew returns a mutated copy, we can't just
         * apply it to sub_action; we have to remember to update the sublink
         * inside rule_action, too.
         */
        if (event == CMD_INSERT || event == CMD_UPDATE)
        {
                sub_action = (Query *) ResolveNew((Node *) sub_action,
                                                                                  new_varno,
                                                                                  0,
                                                                                  parsetree->targetList,
                                                                                  event,
                                                                                  current_varno);
                if (sub_action_ptr)
                        *sub_action_ptr = sub_action;
                else
                        rule_action = sub_action;
        }

        return rule_action;
}

/*
 * Copy the query's jointree list, and optionally attempt to remove any
 * occurrence of the given rt_index as a top-level join item (we do not look
 * for it within join items; this is OK because we are only expecting to find
 * it as an UPDATE or DELETE target relation, which will be at the top level
 * of the join).  Returns modified jointree list --- this is a separate copy
 * sharing no nodes with the original.
 */
static List *
adjustJoinTreeList(Query *parsetree, bool removert, int rt_index)
{
        List       *newjointree = copyObject(parsetree->jointree->fromlist);
        List       *jjt;

        if (removert)
        {
                foreach(jjt, newjointree)
                {
                        RangeTblRef *rtr = lfirst(jjt);

                        if (IsA(rtr, RangeTblRef) &&
                                rtr->rtindex == rt_index)
                        {
                                newjointree = lremove(rtr, newjointree);
                                /* foreach is safe because we exit loop after lremove... */
                                break;
                        }
                }
        }
        return newjointree;
}


/*
 * rewriteTargetList - rewrite INSERT/UPDATE targetlist into standard form
 *
 * This has the following responsibilities:
 *
 * 1. For an INSERT, add tlist entries to compute default values for any
 * attributes that have defaults and are not assigned to in the given tlist.
 * (We do not insert anything for default-less attributes, however.  The
 * planner will later insert NULLs for them, but there's no reason to slow
 * down rewriter processing with extra tlist nodes.)  Also, for both INSERT
 * and UPDATE, replace explicit DEFAULT specifications with column default
 * expressions.
 *
 * 2. Merge multiple entries for the same target attribute, or declare error
 * if we can't.  Presently, multiple entries are only allowed for UPDATE of
 * an array field, for example "UPDATE table SET foo[2] = 42, foo[4] = 43".
 * We can merge such operations into a single assignment op.  Essentially,
 * the expression we want to produce in this case is like
 *              foo = array_set(array_set(foo, 2, 42), 4, 43)
 *
 * 3. Sort the tlist into standard order: non-junk fields in order by resno,
 * then junk fields (these in no particular order).
 *
 * We must do items 1 and 2 before firing rewrite rules, else rewritten
 * references to NEW.foo will produce wrong or incomplete results.      Item 3
 * is not needed for rewriting, but will be needed by the planner, and we
 * can do it essentially for free while handling items 1 and 2.
 */
static void
rewriteTargetList(Query *parsetree, Relation target_relation)
{
        CmdType         commandType = parsetree->commandType;
        List       *tlist = parsetree->targetList;
        List       *new_tlist = NIL;
        int                     attrno,
                                numattrs;
        List       *temp;

        /*
         * Scan the tuple description in the relation's relcache entry to make
         * sure we have all the user attributes in the right order.
         */
        numattrs = RelationGetNumberOfAttributes(target_relation);

        for (attrno = 1; attrno <= numattrs; attrno++)
        {
                Form_pg_attribute att_tup = target_relation->rd_att->attrs[attrno - 1];
                TargetEntry *new_tle = NULL;

                /* We can ignore deleted attributes */
                if (att_tup->attisdropped)
                        continue;

                /*
                 * Look for targetlist entries matching this attr.      We match by
                 * resno, but the resname should match too.
                 *
                 * Junk attributes are not candidates to be matched.
                 */
                foreach(temp, tlist)
                {
                        TargetEntry *old_tle = (TargetEntry *) lfirst(temp);
                        Resdom     *resdom = old_tle->resdom;

                        if (!resdom->resjunk && resdom->resno == attrno)
                        {
                                Assert(strcmp(resdom->resname,
                                                          NameStr(att_tup->attname)) == 0);
                                new_tle = process_matched_tle(old_tle, new_tle);
                                /* keep scanning to detect multiple assignments to attr */
                        }
                }

                /*
                 * Handle the two cases where we need to insert a default expression:
                 * it's an INSERT and there's no tlist entry for the column, or the
                 * tlist entry is a DEFAULT placeholder node.
                 */
                if ((new_tle == NULL && commandType == CMD_INSERT) ||
                        (new_tle && new_tle->expr && IsA(new_tle->expr, SetToDefault)))
                {
                        Node       *new_expr;

                        new_expr = build_column_default(target_relation, attrno);

                        /*
                         * If there is no default (ie, default is effectively NULL),
                         * we can omit the tlist entry in the INSERT case, since the
                         * planner can insert a NULL for itself, and there's no point
                         * in spending any more rewriter cycles on the entry.  But in the
                         * UPDATE case we've got to explicitly set the column to NULL.
                         */
                        if (!new_expr)
                        {
                                if (commandType == CMD_INSERT)
                                        new_tle = NULL;
                                else
                                {
                                        new_expr = (Node *) makeConst(att_tup->atttypid,
                                                                                                  att_tup->attlen,
                                                                                                  (Datum) 0,
                                                                                                  true, /* isnull */
                                                                                                  att_tup->attbyval);
                                        /* this is to catch a NOT NULL domain constraint */
                                        new_expr = coerce_to_domain(new_expr,
                                                                                                InvalidOid,
                                                                                                att_tup->atttypid,
                                                                                                COERCE_IMPLICIT_CAST);
                                }
                        }

                        if (new_expr)
                                new_tle = makeTargetEntry(makeResdom(attrno,
                                                                                                         att_tup->atttypid,
                                                                                                         att_tup->atttypmod,
                                                                          pstrdup(NameStr(att_tup->attname)),
                                                                                                         false),
                                                                                  (Expr *) new_expr);
                }

                if (new_tle)
                        new_tlist = lappend(new_tlist, new_tle);
        }

        /*
         * Copy all resjunk tlist entries to the end of the new tlist, and
         * assign them resnos above the last real resno.
         *
         * Typical junk entries include ORDER BY or GROUP BY expressions (are
         * these actually possible in an INSERT or UPDATE?), system attribute
         * references, etc.
         */
        foreach(temp, tlist)
        {
                TargetEntry *old_tle = (TargetEntry *) lfirst(temp);
                Resdom     *resdom = old_tle->resdom;

                if (resdom->resjunk)
                {
                        /* Get the resno right, but don't copy unnecessarily */
                        if (resdom->resno != attrno)
                        {
                                resdom = (Resdom *) copyObject((Node *) resdom);
                                resdom->resno = attrno;
                                old_tle = makeTargetEntry(resdom, old_tle->expr);
                        }
                        new_tlist = lappend(new_tlist, old_tle);
                        attrno++;
                }
                else
                {
                        /* Let's just make sure we processed all the non-junk items */
                        if (resdom->resno < 1 || resdom->resno > numattrs)
                                elog(ERROR, "rewriteTargetList: bogus resno %d in targetlist",
                                         resdom->resno);
                }
        }

        parsetree->targetList = new_tlist;
}


/*
 * Convert a matched TLE from the original tlist into a correct new TLE.
 *
 * This routine detects and handles multiple assignments to the same target
 * attribute.
 */
static TargetEntry *
process_matched_tle(TargetEntry *src_tle,
                                        TargetEntry *prior_tle)
{
        Resdom     *resdom = src_tle->resdom;
        Node       *priorbottom;
        ArrayRef   *newexpr;

        if (prior_tle == NULL)
        {
                /*
                 * Normal case where this is the first assignment to the
                 * attribute.
                 */
                return src_tle;
        }

        /*
         * Multiple assignments to same attribute.      Allow only if all are
         * array-assign operators with same bottom array object.
         */
        if (src_tle->expr == NULL || !IsA(src_tle->expr, ArrayRef) ||
                ((ArrayRef *) src_tle->expr)->refassgnexpr == NULL ||
                prior_tle->expr == NULL || !IsA(prior_tle->expr, ArrayRef) ||
                ((ArrayRef *) prior_tle->expr)->refassgnexpr == NULL ||
                ((ArrayRef *) src_tle->expr)->refrestype !=
                ((ArrayRef *) prior_tle->expr)->refrestype)
                elog(ERROR, "Multiple assignments to same attribute \"%s\"",
                         resdom->resname);

        /*
         * Prior TLE could be a nest of ArrayRefs if we do this more than
         * once.
         */
        priorbottom = (Node *) ((ArrayRef *) prior_tle->expr)->refexpr;
        while (priorbottom != NULL && IsA(priorbottom, ArrayRef) &&
                   ((ArrayRef *) priorbottom)->refassgnexpr != NULL)
                priorbottom = (Node *) ((ArrayRef *) priorbottom)->refexpr;
        if (!equal(priorbottom, ((ArrayRef *) src_tle->expr)->refexpr))
                elog(ERROR, "Multiple assignments to same attribute \"%s\"",
                         resdom->resname);

        /*
         * Looks OK to nest 'em.
         */
        newexpr = makeNode(ArrayRef);
        memcpy(newexpr, src_tle->expr, sizeof(ArrayRef));
        newexpr->refexpr = prior_tle->expr;

        return makeTargetEntry(resdom, (Expr *) newexpr);
}


/*
 * Make an expression tree for the default value for a column.
 *
 * If there is no default, return a NULL instead.
 */
Node *
build_column_default(Relation rel, int attrno)
{
        TupleDesc       rd_att = rel->rd_att;
        Form_pg_attribute att_tup = rd_att->attrs[attrno - 1];
        Oid                     atttype = att_tup->atttypid;
        int32           atttypmod = att_tup->atttypmod;
        Node       *expr = NULL;
        Oid                     exprtype;

        /*
         * Scan to see if relation has a default for this column.
         */
        if (rd_att->constr && rd_att->constr->num_defval > 0)
        {
                AttrDefault *defval = rd_att->constr->defval;
                int                     ndef = rd_att->constr->num_defval;

                while (--ndef >= 0)
                {
                        if (attrno == defval[ndef].adnum)
                        {
                                /*
                                 * Found it, convert string representation to node tree.
                                 */
                                expr = stringToNode(defval[ndef].adbin);
                                break;
                        }
                }
        }

        if (expr == NULL)
        {
                /*
                 * No per-column default, so look for a default for the type
                 * itself.
                 */
                if (att_tup->attisset)
                {
                        /*
                         * Set attributes are represented as OIDs no matter what the
                         * set element type is, and the element type's default is
                         * irrelevant too.
                         */
                }
                else
                        expr = get_typdefault(atttype);
        }

        if (expr == NULL)
                return NULL;                    /* No default anywhere */

        /*
         * Make sure the value is coerced to the target column type (might not
         * be right type yet if it's not a constant!)  This should match the
         * parser's processing of non-defaulted expressions --- see
         * updateTargetListEntry().
         */
        exprtype = exprType(expr);

        expr = coerce_to_target_type(NULL, /* no UNKNOWN params here */
                                                                 expr, exprtype,
                                                                 atttype, atttypmod,
                                                                 COERCION_ASSIGNMENT,
                                                                 COERCE_IMPLICIT_CAST);
        /*
         * This really shouldn't fail; should have checked the default's
         * type when it was created ...
         */
        if (expr == NULL)
                elog(ERROR, "Column \"%s\" is of type %s"
                         " but default expression is of type %s"
                         "\n\tYou will need to rewrite or cast the expression",
                         NameStr(att_tup->attname),
                         format_type_be(atttype),
                         format_type_be(exprtype));

        return expr;
}


/*
 * matchLocks -
 *        match the list of locks and returns the matching rules
 */
static List *
matchLocks(CmdType event,
                   RuleLock *rulelocks,
                   int varno,
                   Query *parsetree)
{
        List       *matching_locks = NIL;
        int                     nlocks;
        int                     i;

        if (rulelocks == NULL)
                return NIL;

        if (parsetree->commandType != CMD_SELECT)
        {
                if (parsetree->resultRelation != varno)
                        return NIL;
        }

        nlocks = rulelocks->numLocks;

        for (i = 0; i < nlocks; i++)
        {
                RewriteRule *oneLock = rulelocks->rules[i];

                if (oneLock->event == event)
                {
                        if (parsetree->commandType != CMD_SELECT ||
                                (oneLock->attrno == -1 ?
                                 rangeTableEntry_used((Node *) parsetree, varno, 0) :
                                 attribute_used((Node *) parsetree,
                                                                varno, oneLock->attrno, 0)))
                                matching_locks = lappend(matching_locks, oneLock);
                }
        }

        return matching_locks;
}


static Query *
ApplyRetrieveRule(Query *parsetree,
                                  RewriteRule *rule,
                                  int rt_index,
                                  bool relation_level,
                                  Relation relation,
                                  bool relIsUsed,
                                  List *activeRIRs)
{
        Query      *rule_action;
        RangeTblEntry *rte,
                           *subrte;

        if (length(rule->actions) != 1)
                elog(ERROR, "ApplyRetrieveRule: expected just one rule action");
        if (rule->qual != NULL)
                elog(ERROR, "ApplyRetrieveRule: can't handle qualified ON SELECT rule");
        if (!relation_level)
                elog(ERROR, "ApplyRetrieveRule: can't handle per-attribute ON SELECT rule");

        /*
         * Make a modifiable copy of the view query, and recursively expand
         * any view references inside it.
         */
        rule_action = copyObject(lfirst(rule->actions));

        rule_action = fireRIRrules(rule_action, activeRIRs);

        /*
         * VIEWs are really easy --- just plug the view query in as a
         * subselect, replacing the relation's original RTE.
         */
        rte = rt_fetch(rt_index, parsetree->rtable);

        rte->rtekind = RTE_SUBQUERY;
        rte->relid = InvalidOid;
        rte->subquery = rule_action;
        rte->inh = false;                       /* must not be set for a subquery */

        /*
         * We move the view's permission check data down to its rangetable.
         * The checks will actually be done against the *OLD* entry therein.
         */
        subrte = rt_fetch(PRS2_OLD_VARNO, rule_action->rtable);
        Assert(subrte->relid == relation->rd_id);
        subrte->checkForRead = rte->checkForRead;
        subrte->checkForWrite = rte->checkForWrite;
        subrte->checkAsUser = rte->checkAsUser;

        rte->checkForRead = false;      /* no permission check on subquery itself */
        rte->checkForWrite = false;
        rte->checkAsUser = InvalidOid;

        /*
         * FOR UPDATE of view?
         */
        if (intMember(rt_index, parsetree->rowMarks))
        {
                /*
                 * Remove the view from the list of rels that will actually be
                 * marked FOR UPDATE by the executor.  It will still be access-
                 * checked for write access, though.
                 */
                parsetree->rowMarks = lremovei(rt_index, parsetree->rowMarks);

                /*
                 * Set up the view's referenced tables as if FOR UPDATE.
                 */
                markQueryForUpdate(rule_action, true);
        }

        return parsetree;
}

/*
 * Recursively mark all relations used by a view as FOR UPDATE.
 *
 * This may generate an invalid query, eg if some sub-query uses an
 * aggregate.  We leave it to the planner to detect that.
 *
 * NB: this must agree with the parser's transformForUpdate() routine.
 */
static void
markQueryForUpdate(Query *qry, bool skipOldNew)
{
        Index           rti = 0;
        List       *l;

        foreach(l, qry->rtable)
        {
                RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

                rti++;

                /* Ignore OLD and NEW entries if we are at top level of view */
                if (skipOldNew &&
                        (rti == PRS2_OLD_VARNO || rti == PRS2_NEW_VARNO))
                        continue;

                if (rte->rtekind == RTE_RELATION)
                {
                        if (!intMember(rti, qry->rowMarks))
                                qry->rowMarks = lappendi(qry->rowMarks, rti);
                        rte->checkForWrite = true;
                }
                else if (rte->rtekind == RTE_SUBQUERY)
                {
                        /* FOR UPDATE of subquery is propagated to subquery's rels */
                        markQueryForUpdate(rte->subquery, false);
                }
        }
}


/*
 * fireRIRonSubLink -
 *      Apply fireRIRrules() to each SubLink (subselect in expression) found
 *      in the given tree.
 *
 * NOTE: although this has the form of a walker, we cheat and modify the
 * SubLink nodes in-place.      It is caller's responsibility to ensure that
 * no unwanted side-effects occur!
 *
 * This is unlike most of the other routines that recurse into subselects,
 * because we must take control at the SubLink node in order to replace
 * the SubLink's subselect link with the possibly-rewritten subquery.
 */
static bool
fireRIRonSubLink(Node *node, List *activeRIRs)
{
        if (node == NULL)
                return false;
        if (IsA(node, SubLink))
        {
                SubLink    *sub = (SubLink *) node;

                /* Do what we came for */
                sub->subselect = (Node *) fireRIRrules((Query *) sub->subselect,
                                                                                           activeRIRs);
                /* Fall through to process lefthand args of SubLink */
        }

        /*
         * Do NOT recurse into Query nodes, because fireRIRrules already
         * processed subselects of subselects for us.
         */
        return expression_tree_walker(node, fireRIRonSubLink,
                                                                  (void *) activeRIRs);
}


/*
 * fireRIRrules -
 *      Apply all RIR rules on each rangetable entry in a query
 */
static Query *
fireRIRrules(Query *parsetree, List *activeRIRs)
{
        int                     rt_index;

        /*
         * don't try to convert this into a foreach loop, because rtable list
         * can get changed each time through...
         */
        rt_index = 0;
        while (rt_index < length(parsetree->rtable))
        {
                RangeTblEntry *rte;
                Relation        rel;
                List       *locks;
                RuleLock   *rules;
                RewriteRule *rule;
                LOCKMODE        lockmode;
                bool            relIsUsed;
                int                     i;

                ++rt_index;

                rte = rt_fetch(rt_index, parsetree->rtable);

                /*
                 * A subquery RTE can't have associated rules, so there's nothing
                 * to do to this level of the query, but we must recurse into the
                 * subquery to expand any rule references in it.
                 */
                if (rte->rtekind == RTE_SUBQUERY)
                {
                        rte->subquery = fireRIRrules(rte->subquery, activeRIRs);
                        continue;
                }

                /*
                 * Joins and other non-relation RTEs can be ignored completely.
                 */
                if (rte->rtekind != RTE_RELATION)
                        continue;

                /*
                 * If the table is not referenced in the query, then we ignore it.
                 * This prevents infinite expansion loop due to new rtable entries
                 * inserted by expansion of a rule. A table is referenced if it is
                 * part of the join set (a source table), or is referenced by any
                 * Var nodes, or is the result table.
                 */
                relIsUsed = rangeTableEntry_used((Node *) parsetree, rt_index, 0);

                if (!relIsUsed && rt_index != parsetree->resultRelation)
                        continue;

                /*
                 * This may well be the first access to the relation during the
                 * current statement (it will be, if this Query was extracted from
                 * a rule or somehow got here other than via the parser).
                 * Therefore, grab the appropriate lock type for the relation, and
                 * do not release it until end of transaction.  This protects the
                 * rewriter and planner against schema changes mid-query.
                 *
                 * If the relation is the query's result relation, then
                 * RewriteQuery() already got the right lock on it, so we need no
                 * additional lock. Otherwise, check to see if the relation is
                 * accessed FOR UPDATE or not.
                 */
                if (rt_index == parsetree->resultRelation)
                        lockmode = NoLock;
                else if (intMember(rt_index, parsetree->rowMarks))
                        lockmode = RowShareLock;
                else
                        lockmode = AccessShareLock;

                rel = heap_open(rte->relid, lockmode);

                /*
                 * Collect the RIR rules that we must apply
                 */
                rules = rel->rd_rules;
                if (rules == NULL)
                {
                        heap_close(rel, NoLock);
                        continue;
                }
                locks = NIL;
                for (i = 0; i < rules->numLocks; i++)
                {
                        rule = rules->rules[i];
                        if (rule->event != CMD_SELECT)
                                continue;

                        if (rule->attrno > 0)
                        {
                                /* per-attr rule; do we need it? */
                                if (!attribute_used((Node *) parsetree, rt_index,
                                                                        rule->attrno, 0))
                                        continue;
                        }

                        locks = lappend(locks, rule);
                }

                /*
                 * If we found any, apply them --- but first check for recursion!
                 */
                if (locks != NIL)
                {
                        List       *newActiveRIRs;
                        List       *l;

                        if (oidMember(RelationGetRelid(rel), activeRIRs))
                                elog(ERROR, "Infinite recursion detected in rules for relation %s",
                                         RelationGetRelationName(rel));
                        newActiveRIRs = lconso(RelationGetRelid(rel), activeRIRs);

                        foreach(l, locks)
                        {
                                rule = lfirst(l);

                                parsetree = ApplyRetrieveRule(parsetree,
                                                                                          rule,
                                                                                          rt_index,
                                                                                          rule->attrno == -1,
                                                                                          rel,
                                                                                          relIsUsed,
                                                                                          newActiveRIRs);
                        }
                }

                heap_close(rel, NoLock);
        }

        /*
         * Recurse into sublink subqueries, too.  But we already did the ones
         * in the rtable.
         */
        if (parsetree->hasSubLinks)
                query_tree_walker(parsetree, fireRIRonSubLink, (void *) activeRIRs,
                                                  QTW_IGNORE_RT_SUBQUERIES);

        /*
         * If the query was marked having aggregates, check if this is still
         * true after rewriting.  Ditto for sublinks.  Note there should be no
         * aggs in the qual at this point.      (Does this code still do anything
         * useful?      The view-becomes-subselect-in-FROM approach doesn't look
         * like it could remove aggs or sublinks...)
         */
        if (parsetree->hasAggs)
        {
                parsetree->hasAggs = checkExprHasAggs((Node *) parsetree);
                if (parsetree->hasAggs)
                        if (checkExprHasAggs((Node *) parsetree->jointree))
                                elog(ERROR, "fireRIRrules: failed to remove aggs from qual");
        }
        if (parsetree->hasSubLinks)
                parsetree->hasSubLinks = checkExprHasSubLink((Node *) parsetree);

        return parsetree;
}


/*
 * Modify the given query by adding 'AND rule_qual IS NOT TRUE' to its
 * qualification.  This is used to generate suitable "else clauses" for
 * conditional INSTEAD rules.  (Unfortunately we must use "x IS NOT TRUE",
 * not just "NOT x" which the planner is much smarter about, else we will
 * do the wrong thing when the qual evaluates to NULL.)
 *
 * The rule_qual may contain references to OLD or NEW.  OLD references are
 * replaced by references to the specified rt_index (the relation that the
 * rule applies to).  NEW references are only possible for INSERT and UPDATE
 * queries on the relation itself, and so they should be replaced by copies
 * of the related entries in the query's own targetlist.
 */
static Query *
CopyAndAddInvertedQual(Query *parsetree,
                                           Node *rule_qual,
                                           int rt_index,
                                           CmdType event)
{
        Query      *new_tree = (Query *) copyObject(parsetree);
        Node       *new_qual = (Node *) copyObject(rule_qual);

        /* Fix references to OLD */
        ChangeVarNodes(new_qual, PRS2_OLD_VARNO, rt_index, 0);
        /* Fix references to NEW */
        if (event == CMD_INSERT || event == CMD_UPDATE)
                new_qual = ResolveNew(new_qual,
                                                          PRS2_NEW_VARNO,
                                                          0,
                                                          parsetree->targetList,
                                                          event,
                                                          rt_index);
        /* And attach the fixed qual */
        AddInvertedQual(new_tree, new_qual);

        return new_tree;
}


/*
 *      fireRules -
 *         Iterate through rule locks applying rules.
 *
 * Input arguments:
 *      parsetree - original query
 *      rt_index - RT index of result relation in original query
 *      event - type of rule event
 *      locks - list of rules to fire
 * Output arguments:
 *      *instead_flag - set TRUE if any unqualified INSTEAD rule is found
 *                                      (must be initialized to FALSE)
 *      *qual_product - filled with modified original query if any qualified
 *                                      INSTEAD rule is found (must be initialized to NULL)
 * Return value:
 *      list of rule actions adjusted for use with this query
 *
 * Qualified INSTEAD rules generate their action with the qualification
 * condition added.  They also generate a modified version of the original
 * query with the negated qualification added, so that it will run only for
 * rows that the qualified action doesn't act on.  (If there are multiple
 * qualified INSTEAD rules, we AND all the negated quals onto a single
 * modified original query.)  We won't execute the original, unmodified
 * query if we find either qualified or unqualified INSTEAD rules.  If
 * we find both, the modified original query is discarded too.
 */
static List *
fireRules(Query *parsetree,
                  int rt_index,
                  CmdType event,
                  List *locks,
                  bool *instead_flag,
                  Query **qual_product)
{
        List       *results = NIL;
        List       *i;

        foreach(i, locks)
        {
                RewriteRule *rule_lock = (RewriteRule *) lfirst(i);
                Node       *event_qual = rule_lock->qual;
                List       *actions = rule_lock->actions;
                QuerySource     qsrc;
                List       *r;

                /* Determine correct QuerySource value for actions */
                if (rule_lock->isInstead)
                {
                        if (event_qual != NULL)
                                qsrc = QSRC_QUAL_INSTEAD_RULE;
                        else
                        {
                                qsrc = QSRC_INSTEAD_RULE;
                                *instead_flag = true; /* report unqualified INSTEAD */
                        }
                }
                else
                        qsrc = QSRC_NON_INSTEAD_RULE;

                if (qsrc == QSRC_QUAL_INSTEAD_RULE)
                {
                        /*
                         * If there are INSTEAD rules with qualifications, the
                         * original query is still performed. But all the negated rule
                         * qualifications of the INSTEAD rules are added so it does
                         * its actions only in cases where the rule quals of all
                         * INSTEAD rules are false. Think of it as the default action
                         * in a case. We save this in *qual_product so
                         * RewriteQuery() can add it to the query list after we
                         * mangled it up enough.
                         *
                         * If we have already found an unqualified INSTEAD rule,
                         * then *qual_product won't be used, so don't bother building it.
                         */
                        if (! *instead_flag)
                        {
                                if (*qual_product == NULL)
                                        *qual_product = parsetree;
                                *qual_product = CopyAndAddInvertedQual(*qual_product,
                                                                                                           event_qual,
                                                                                                           rt_index,
                                                                                                           event);
                        }
                }

                /* Now process the rule's actions and add them to the result list */
                foreach(r, actions)
                {
                        Query      *rule_action = lfirst(r);

                        if (rule_action->commandType == CMD_NOTHING)
                                continue;

                        rule_action = rewriteRuleAction(parsetree, rule_action,
                                                                                        event_qual, rt_index, event);

                        rule_action->querySource = qsrc;
                        rule_action->canSetTag = false;         /* might change later */

                        results = lappend(results, rule_action);
                }
        }

        return results;
}


/*
 * RewriteQuery -
 *        rewrites the query and apply the rules again on the queries rewritten
 *
 * rewrite_events is a list of open query-rewrite actions, so we can detect
 * infinite recursion.
 */
static List *
RewriteQuery(Query *parsetree, List *rewrite_events)
{
        CmdType         event = parsetree->commandType;
        bool            instead = false;
        Query      *qual_product = NULL;
        List       *rewritten = NIL;

        /*
         * If the statement is an update, insert or delete - fire rules on it.
         *
         * SELECT rules are handled later when we have all the queries that
         * should get executed.  Also, utilities aren't rewritten at all
         * (do we still need that check?)
         */
        if (event != CMD_SELECT && event != CMD_UTILITY)
        {
                int                     result_relation;
                RangeTblEntry *rt_entry;
                Relation        rt_entry_relation;
                List       *locks;

                result_relation = parsetree->resultRelation;
                Assert(result_relation != 0);
                rt_entry = rt_fetch(result_relation, parsetree->rtable);
                Assert(rt_entry->rtekind == RTE_RELATION);

                /*
                 * This may well be the first access to the result relation during the
                 * current statement (it will be, if this Query was extracted from a
                 * rule or somehow got here other than via the parser). Therefore,
                 * grab the appropriate lock type for a result relation, and do not
                 * release it until end of transaction.  This protects the rewriter
                 * and planner against schema changes mid-query.
                 */
                rt_entry_relation = heap_open(rt_entry->relid, RowExclusiveLock);

                /*
                 * If it's an INSERT or UPDATE, rewrite the targetlist into standard
                 * form.  This will be needed by the planner anyway, and doing it now
                 * ensures that any references to NEW.field will behave sanely.
                 */
                if (event == CMD_INSERT || event == CMD_UPDATE)
                        rewriteTargetList(parsetree, rt_entry_relation);

                /*
                 * Collect and apply the appropriate rules.
                 */
                locks = matchLocks(event, rt_entry_relation->rd_rules,
                                                   result_relation, parsetree);

                if (locks != NIL)
                {
                        List       *product_queries;

                        product_queries = fireRules(parsetree,
                                                                                result_relation,
                                                                                event,
                                                                                locks,
                                                                                &instead,
                                                                                &qual_product);

                        /*
                         * If we got any product queries, recursively rewrite them
                         * --- but first check for recursion!
                         */
                        if (product_queries != NIL)
                        {
                                List       *n;
                                rewrite_event *rev;

                                foreach(n, rewrite_events)
                                {
                                        rev = (rewrite_event *) lfirst(n);
                                        if (rev->relation == RelationGetRelid(rt_entry_relation) &&
                                                rev->event == event)
                                                elog(ERROR, "Infinite recursion detected in rules for relation %s",
                                                         RelationGetRelationName(rt_entry_relation));
                                }

                                rev = (rewrite_event *) palloc(sizeof(rewrite_event));
                                rev->relation = RelationGetRelid(rt_entry_relation);
                                rev->event = event;
                                rewrite_events = lcons(rev, rewrite_events);

                                foreach(n, product_queries)
                                {
                                        Query      *pt = (Query *) lfirst(n);
                                        List       *newstuff;

                                        newstuff = RewriteQuery(pt, rewrite_events);
                                        rewritten = nconc(rewritten, newstuff);
                                }
                        }
                }

                heap_close(rt_entry_relation, NoLock);          /* keep lock! */
        }

        /*
         * For INSERTs, the original query is done first; for UPDATE/DELETE,
         * it is done last.  This is needed because update and delete rule
         * actions might not do anything if they are invoked after the update
         * or delete is performed. The command counter increment between the
         * query executions makes the deleted (and maybe the updated) tuples
         * disappear so the scans for them in the rule actions cannot find
         * them.
         *
         * If we found any unqualified INSTEAD, the original query is not
         * done at all, in any form.  Otherwise, we add the modified form
         * if qualified INSTEADs were found, else the unmodified form.
         */
        if (!instead)
        {
                if (parsetree->commandType == CMD_INSERT)
                {
                        if (qual_product != NULL)
                                rewritten = lcons(qual_product, rewritten);
                        else
                                rewritten = lcons(parsetree, rewritten);
                }
                else
                {
                        if (qual_product != NULL)
                                rewritten = lappend(rewritten, qual_product);
                        else
                                rewritten = lappend(rewritten, parsetree);
                }
        }

        return rewritten;
}


/*
 * QueryRewrite -
 *        Primary entry point to the query rewriter.
 *        Rewrite one query via query rewrite system, possibly returning 0
 *        or many queries.
 *
 * NOTE: The code in QueryRewrite was formerly in pg_parse_and_plan(), and was
 * moved here so that it would be invoked during EXPLAIN.
 */
List *
QueryRewrite(Query *parsetree)
{
        List       *querylist;
        List       *results = NIL;
        List       *l;
        CmdType         origCmdType;
        bool            foundOriginalQuery;
        Query      *lastInstead;

        /*
         * Step 1
         *
         * Apply all non-SELECT rules possibly getting 0 or many queries
         */
        querylist = RewriteQuery(parsetree, NIL);

        /*
         * Step 2
         *
         * Apply all the RIR rules on each query
         */
        foreach(l, querylist)
        {
                Query      *query = (Query *) lfirst(l);

                query = fireRIRrules(query, NIL);

                /*
                 * If the query target was rewritten as a view, complain.
                 */
                if (query->resultRelation)
                {
                        RangeTblEntry *rte = rt_fetch(query->resultRelation,
                                                                                  query->rtable);

                        if (rte->rtekind == RTE_SUBQUERY)
                        {
                                switch (query->commandType)
                                {
                                        case CMD_INSERT:
                                                elog(ERROR, "Cannot insert into a view"
                                                         "\n\tYou need an unconditional ON INSERT DO INSTEAD rule");
                                                break;
                                        case CMD_UPDATE:
                                                elog(ERROR, "Cannot update a view"
                                                         "\n\tYou need an unconditional ON UPDATE DO INSTEAD rule");
                                                break;
                                        case CMD_DELETE:
                                                elog(ERROR, "Cannot delete from a view"
                                                         "\n\tYou need an unconditional ON DELETE DO INSTEAD rule");
                                                break;
                                        default:
                                                elog(ERROR, "QueryRewrite: unexpected commandType %d",
                                                         (int) query->commandType);
                                                break;
                                }
                        }
                }

                results = lappend(results, query);
        }

        /*
         * Step 3
         *
         * Determine which, if any, of the resulting queries is supposed to set
         * the command-result tag; and update the canSetTag fields accordingly.
         *
         * If the original query is still in the list, it sets the command tag.
         * Otherwise, the last INSTEAD query of the same kind as the original
         * is allowed to set the tag.  (Note these rules can leave us with no
         * query setting the tag.  The tcop code has to cope with this by
         * setting up a default tag based on the original un-rewritten query.)
         *
         * The Asserts verify that at most one query in the result list is marked
         * canSetTag.  If we aren't checking asserts, we can fall out of the loop
         * as soon as we find the original query.
         */
        origCmdType = parsetree->commandType;
        foundOriginalQuery = false;
        lastInstead = NULL;

        foreach(l, results)
        {
                Query      *query = (Query *) lfirst(l);

                if (query->querySource == QSRC_ORIGINAL)
                {
                        Assert(query->canSetTag);
                        Assert(!foundOriginalQuery);
                        foundOriginalQuery = true;
#ifndef USE_ASSERT_CHECKING
                        break;
#endif
                }
                else
                {
                        Assert(!query->canSetTag);
                        if (query->commandType == origCmdType &&
                                (query->querySource == QSRC_INSTEAD_RULE ||
                                 query->querySource == QSRC_QUAL_INSTEAD_RULE))
                                lastInstead = query;
                }
        }

        if (!foundOriginalQuery && lastInstead != NULL)
                lastInstead->canSetTag = true;

        return results;
}