/*------------------------------------------------------------------------- * * portalmem.c * backend portal memory management * * Portals are objects representing the execution state of a query. * This module provides memory management services for portals, but it * doesn't actually run the executor for them. * * * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/utils/mmgr/portalmem.c,v 1.83 2005/11/22 18:17:27 momjian Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include "miscadmin.h" #include "commands/portalcmds.h" #include "executor/executor.h" #include "utils/hsearch.h" #include "utils/memutils.h" #include "utils/portal.h" /* * Estimate of the maximum number of open portals a user would have, * used in initially sizing the PortalHashTable in EnablePortalManager(). * Since the hash table can expand, there's no need to make this overly * generous, and keeping it small avoids unnecessary overhead in the * hash_seq_search() calls executed during transaction end. */ #define PORTALS_PER_USER 16 /* ---------------- * Global state * ---------------- */ #define MAX_PORTALNAME_LEN NAMEDATALEN typedef struct portalhashent { char portalname[MAX_PORTALNAME_LEN]; Portal portal; } PortalHashEnt; static HTAB *PortalHashTable = NULL; #define PortalHashTableLookup(NAME, PORTAL) \ do { \ PortalHashEnt *hentry; char key[MAX_PORTALNAME_LEN]; \ \ MemSet(key, 0, MAX_PORTALNAME_LEN); \ StrNCpy(key, NAME, MAX_PORTALNAME_LEN); \ hentry = (PortalHashEnt*)hash_search(PortalHashTable, \ key, HASH_FIND, NULL); \ if (hentry) \ PORTAL = hentry->portal; \ else \ PORTAL = NULL; \ } while(0) #define PortalHashTableInsert(PORTAL, NAME) \ do { \ PortalHashEnt *hentry; bool found; char key[MAX_PORTALNAME_LEN]; \ \ MemSet(key, 0, MAX_PORTALNAME_LEN); \ StrNCpy(key, NAME, MAX_PORTALNAME_LEN); \ hentry = (PortalHashEnt*)hash_search(PortalHashTable, \ key, HASH_ENTER, &found); \ if (found) \ elog(ERROR, "duplicate portal name"); \ hentry->portal = PORTAL; \ /* To avoid duplicate storage, make PORTAL->name point to htab entry */ \ PORTAL->name = hentry->portalname; \ } while(0) #define PortalHashTableDelete(PORTAL) \ do { \ PortalHashEnt *hentry; char key[MAX_PORTALNAME_LEN]; \ \ MemSet(key, 0, MAX_PORTALNAME_LEN); \ StrNCpy(key, PORTAL->name, MAX_PORTALNAME_LEN); \ hentry = (PortalHashEnt*)hash_search(PortalHashTable, \ key, HASH_REMOVE, NULL); \ if (hentry == NULL) \ elog(WARNING, "trying to delete portal name that does not exist"); \ } while(0) static MemoryContext PortalMemory = NULL; /* ---------------------------------------------------------------- * public portal interface functions * ---------------------------------------------------------------- */ /* * EnablePortalManager * Enables the portal management module at backend startup. */ void EnablePortalManager(void) { HASHCTL ctl; Assert(PortalMemory == NULL); PortalMemory = AllocSetContextCreate(TopMemoryContext, "PortalMemory", ALLOCSET_DEFAULT_MINSIZE, ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE); ctl.keysize = MAX_PORTALNAME_LEN; ctl.entrysize = sizeof(PortalHashEnt); /* * use PORTALS_PER_USER as a guess of how many hash table entries to * create, initially */ PortalHashTable = hash_create("Portal hash", PORTALS_PER_USER, &ctl, HASH_ELEM); } /* * GetPortalByName * Returns a portal given a portal name, or NULL if name not found. */ Portal GetPortalByName(const char *name) { Portal portal; if (PointerIsValid(name)) PortalHashTableLookup(name, portal); else portal = NULL; return portal; } /* * CreatePortal * Returns a new portal given a name. * * allowDup: if true, automatically drop any pre-existing portal of the * same name (if false, an error is raised). * * dupSilent: if true, don't even emit a WARNING. */ Portal CreatePortal(const char *name, bool allowDup, bool dupSilent) { Portal portal; AssertArg(PointerIsValid(name)); portal = GetPortalByName(name); if (PortalIsValid(portal)) { if (!allowDup) ereport(ERROR, (errcode(ERRCODE_DUPLICATE_CURSOR), errmsg("cursor \"%s\" already exists", name))); if (!dupSilent) ereport(WARNING, (errcode(ERRCODE_DUPLICATE_CURSOR), errmsg("closing existing cursor \"%s\"", name))); PortalDrop(portal, false); } /* make new portal structure */ portal = (Portal) MemoryContextAllocZero(PortalMemory, sizeof *portal); /* initialize portal heap context; typically it won't store much */ portal->heap = AllocSetContextCreate(PortalMemory, "PortalHeapMemory", ALLOCSET_SMALL_MINSIZE, ALLOCSET_SMALL_INITSIZE, ALLOCSET_SMALL_MAXSIZE); /* create a resource owner for the portal */ portal->resowner = ResourceOwnerCreate(CurTransactionResourceOwner, "Portal"); /* initialize portal fields that don't start off zero */ portal->cleanup = PortalCleanup; portal->createSubid = GetCurrentSubTransactionId(); portal->strategy = PORTAL_MULTI_QUERY; portal->cursorOptions = CURSOR_OPT_NO_SCROLL; portal->atStart = true; portal->atEnd = true; /* disallow fetches until query is set */ /* put portal in table (sets portal->name) */ PortalHashTableInsert(portal, name); return portal; } /* * CreateNewPortal * Create a new portal, assigning it a random nonconflicting name. */ Portal CreateNewPortal(void) { static unsigned int unnamed_portal_count = 0; char portalname[MAX_PORTALNAME_LEN]; /* Select a nonconflicting name */ for (;;) { unnamed_portal_count++; sprintf(portalname, "", unnamed_portal_count); if (GetPortalByName(portalname) == NULL) break; } return CreatePortal(portalname, false, false); } /* * PortalDefineQuery * A simple subroutine to establish a portal's query. * * Notes: commandTag shall be NULL if and only if the original query string * (before rewriting) was an empty string. Also, the passed commandTag must * be a pointer to a constant string, since it is not copied. The caller is * responsible for ensuring that the passed sourceText (if any), parse and * plan trees have adequate lifetime. Also, queryContext must accurately * describe the location of the parse and plan trees. */ void PortalDefineQuery(Portal portal, const char *sourceText, const char *commandTag, List *parseTrees, List *planTrees, MemoryContext queryContext) { AssertArg(PortalIsValid(portal)); AssertState(portal->queryContext == NULL); /* else defined already */ Assert(list_length(parseTrees) == list_length(planTrees)); Assert(commandTag != NULL || parseTrees == NIL); portal->sourceText = sourceText; portal->commandTag = commandTag; portal->parseTrees = parseTrees; portal->planTrees = planTrees; portal->queryContext = queryContext; } /* * PortalCreateHoldStore * Create the tuplestore for a portal. */ void PortalCreateHoldStore(Portal portal) { MemoryContext oldcxt; Assert(portal->holdContext == NULL); Assert(portal->holdStore == NULL); /* * Create the memory context that is used for storage of the tuple set. * Note this is NOT a child of the portal's heap memory. */ portal->holdContext = AllocSetContextCreate(PortalMemory, "PortalHoldContext", ALLOCSET_DEFAULT_MINSIZE, ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE); /* Create the tuple store, selecting cross-transaction temp files. */ oldcxt = MemoryContextSwitchTo(portal->holdContext); /* XXX: Should maintenance_work_mem be used for the portal size? */ portal->holdStore = tuplestore_begin_heap(true, true, work_mem); MemoryContextSwitchTo(oldcxt); } /* * PortalDrop * Destroy the portal. */ void PortalDrop(Portal portal, bool isTopCommit) { AssertArg(PortalIsValid(portal)); /* Not sure if this case can validly happen or not... */ if (portal->status == PORTAL_ACTIVE) elog(ERROR, "cannot drop active portal"); /* * Remove portal from hash table. Because we do this first, we will not * come back to try to remove the portal again if there's any error in the * subsequent steps. Better to leak a little memory than to get into an * infinite error-recovery loop. */ PortalHashTableDelete(portal); /* let portalcmds.c clean up the state it knows about */ if (PointerIsValid(portal->cleanup)) (*portal->cleanup) (portal); /* * Release any resources still attached to the portal. There are several * cases being covered here: * * Top transaction commit (indicated by isTopCommit): normally we should * do nothing here and let the regular end-of-transaction resource * releasing mechanism handle these resources too. However, if we have a * FAILED portal (eg, a cursor that got an error), we'd better clean up * its resources to avoid resource-leakage warning messages. * * Sub transaction commit: never comes here at all, since we don't kill * any portals in AtSubCommit_Portals(). * * Main or sub transaction abort: we will do nothing here because * portal->resowner was already set NULL; the resources were already * cleaned up in transaction abort. * * Ordinary portal drop: must release resources. However, if the portal * is not FAILED then we do not release its locks. The locks become the * responsibility of the transaction's ResourceOwner (since it is the * parent of the portal's owner) and will be released when the transaction * eventually ends. */ if (portal->resowner && (!isTopCommit || portal->status == PORTAL_FAILED)) { bool isCommit = (portal->status != PORTAL_FAILED); ResourceOwnerRelease(portal->resowner, RESOURCE_RELEASE_BEFORE_LOCKS, isCommit, false); ResourceOwnerRelease(portal->resowner, RESOURCE_RELEASE_LOCKS, isCommit, false); ResourceOwnerRelease(portal->resowner, RESOURCE_RELEASE_AFTER_LOCKS, isCommit, false); ResourceOwnerDelete(portal->resowner); } portal->resowner = NULL; /* * Delete tuplestore if present. We should do this even under error * conditions; since the tuplestore would have been using cross- * transaction storage, its temp files need to be explicitly deleted. */ if (portal->holdStore) { MemoryContext oldcontext; oldcontext = MemoryContextSwitchTo(portal->holdContext); tuplestore_end(portal->holdStore); MemoryContextSwitchTo(oldcontext); portal->holdStore = NULL; } /* delete tuplestore storage, if any */ if (portal->holdContext) MemoryContextDelete(portal->holdContext); /* release subsidiary storage */ MemoryContextDelete(PortalGetHeapMemory(portal)); /* release portal struct (it's in PortalMemory) */ pfree(portal); } /* * DropDependentPortals * Drop any portals using the specified context as queryContext. * * This is normally used to make sure we can safely drop a prepared statement. */ void DropDependentPortals(MemoryContext queryContext) { HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; if (portal->queryContext == queryContext) PortalDrop(portal, false); } } /* * Pre-commit processing for portals. * * Any holdable cursors created in this transaction need to be converted to * materialized form, since we are going to close down the executor and * release locks. Other portals are not touched yet. * * Returns TRUE if any holdable cursors were processed, FALSE if not. */ bool CommitHoldablePortals(void) { bool result = false; HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; /* Is it a holdable portal created in the current xact? */ if ((portal->cursorOptions & CURSOR_OPT_HOLD) && portal->createSubid != InvalidSubTransactionId && portal->status == PORTAL_READY) { /* * We are exiting the transaction that created a holdable cursor. * Instead of dropping the portal, prepare it for access by later * transactions. * * Note that PersistHoldablePortal() must release all resources * used by the portal that are local to the creating transaction. */ PortalCreateHoldStore(portal); PersistHoldablePortal(portal); /* * Any resources belonging to the portal will be released in the * upcoming transaction-wide cleanup; the portal will no longer * have its own resources. */ portal->resowner = NULL; /* * Having successfully exported the holdable cursor, mark it as * not belonging to this transaction. */ portal->createSubid = InvalidSubTransactionId; result = true; } } return result; } /* * Pre-prepare processing for portals. * * Currently we refuse PREPARE if the transaction created any holdable * cursors, since it's quite unclear what to do with one. However, this * has the same API as CommitHoldablePortals and is invoked in the same * way by xact.c, so that we can easily do something reasonable if anyone * comes up with something reasonable to do. * * Returns TRUE if any holdable cursors were processed, FALSE if not. */ bool PrepareHoldablePortals(void) { bool result = false; HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; /* Is it a holdable portal created in the current xact? */ if ((portal->cursorOptions & CURSOR_OPT_HOLD) && portal->createSubid != InvalidSubTransactionId && portal->status == PORTAL_READY) { /* * We are exiting the transaction that created a holdable cursor. * Can't do PREPARE. */ ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("cannot PREPARE a transaction that has created a cursor WITH HOLD"))); } } return result; } /* * Pre-commit processing for portals. * * Remove all non-holdable portals created in this transaction. * Portals remaining from prior transactions should be left untouched. */ void AtCommit_Portals(void) { HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; /* * Do not touch active portals --- this can only happen in the case of * a multi-transaction utility command, such as VACUUM. * * Note however that any resource owner attached to such a portal is * still going to go away, so don't leave a dangling pointer. */ if (portal->status == PORTAL_ACTIVE) { portal->resowner = NULL; continue; } /* * Do nothing to cursors held over from a previous transaction * (including holdable ones just frozen by CommitHoldablePortals). */ if (portal->createSubid == InvalidSubTransactionId) continue; /* Zap all non-holdable portals */ PortalDrop(portal, true); /* Restart the iteration */ hash_seq_init(&status, PortalHashTable); } } /* * Abort processing for portals. * * At this point we reset "active" status and run the cleanup hook if * present, but we can't release memory until the cleanup call. * * The reason we need to reset active is so that we can replace the unnamed * portal, else we'll fail to execute ROLLBACK when it arrives. */ void AtAbort_Portals(void) { HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; if (portal->status == PORTAL_ACTIVE) portal->status = PORTAL_FAILED; /* * Do nothing else to cursors held over from a previous transaction. */ if (portal->createSubid == InvalidSubTransactionId) continue; /* let portalcmds.c clean up the state it knows about */ if (PointerIsValid(portal->cleanup)) { (*portal->cleanup) (portal); portal->cleanup = NULL; } /* * Any resources belonging to the portal will be released in the * upcoming transaction-wide cleanup; they will be gone before we run * PortalDrop. */ portal->resowner = NULL; } } /* * Post-abort cleanup for portals. * * Delete all portals not held over from prior transactions. */ void AtCleanup_Portals(void) { HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; /* Do nothing to cursors held over from a previous transaction */ if (portal->createSubid == InvalidSubTransactionId) { Assert(portal->status != PORTAL_ACTIVE); Assert(portal->resowner == NULL); continue; } /* Else zap it. */ PortalDrop(portal, false); } } /* * Pre-subcommit processing for portals. * * Reassign the portals created in the current subtransaction to the parent * subtransaction. */ void AtSubCommit_Portals(SubTransactionId mySubid, SubTransactionId parentSubid, ResourceOwner parentXactOwner) { HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; if (portal->createSubid == mySubid) { portal->createSubid = parentSubid; if (portal->resowner) ResourceOwnerNewParent(portal->resowner, parentXactOwner); } } } /* * Subtransaction abort handling for portals. * * Deactivate portals created during the failed subtransaction. * Note that per AtSubCommit_Portals, this will catch portals created * in descendants of the subtransaction too. * * We don't destroy any portals here; that's done in AtSubCleanup_Portals. */ void AtSubAbort_Portals(SubTransactionId mySubid, SubTransactionId parentSubid, ResourceOwner parentXactOwner) { HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; if (portal->createSubid != mySubid) continue; /* * Force any active portals of my own transaction into FAILED state. * This is mostly to ensure that a portal running a FETCH will go * FAILED if the underlying cursor fails. (Note we do NOT want to do * this to upper-level portals, since they may be able to continue.) * * This is only needed to dodge the sanity check in PortalDrop. */ if (portal->status == PORTAL_ACTIVE) portal->status = PORTAL_FAILED; /* * If the portal is READY then allow it to survive into the parent * transaction; otherwise shut it down. * * Currently, we can't actually support that because the portal's * query might refer to objects created or changed in the failed * subtransaction, leading to crashes if execution is resumed. So, * even READY portals are deleted. It would be nice to detect whether * the query actually depends on any such object, instead. */ #ifdef NOT_USED if (portal->status == PORTAL_READY) { portal->createSubid = parentSubid; if (portal->resowner) ResourceOwnerNewParent(portal->resowner, parentXactOwner); } else #endif { /* let portalcmds.c clean up the state it knows about */ if (PointerIsValid(portal->cleanup)) { (*portal->cleanup) (portal); portal->cleanup = NULL; } /* * Any resources belonging to the portal will be released in the * upcoming transaction-wide cleanup; they will be gone before we * run PortalDrop. */ portal->resowner = NULL; } } } /* * Post-subabort cleanup for portals. * * Drop all portals created in the failed subtransaction (but note that * we will not drop any that were reassigned to the parent above). */ void AtSubCleanup_Portals(SubTransactionId mySubid) { HASH_SEQ_STATUS status; PortalHashEnt *hentry; hash_seq_init(&status, PortalHashTable); while ((hentry = (PortalHashEnt *) hash_seq_search(&status)) != NULL) { Portal portal = hentry->portal; if (portal->createSubid != mySubid) continue; /* Zap it. */ PortalDrop(portal, false); } }