portalmem.c

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/*-------------------------------------------------------------------------
 *
 * 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) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/utils/mmgr/portalmem.c,v 1.106.2.1 2008/04/02 18:32:00 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "access/xact.h"
#include "catalog/pg_type.h"
#include "commands/portalcmds.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/memutils.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; \
	\
	hentry = (PortalHashEnt *) hash_search(PortalHashTable, \
										   (NAME), HASH_FIND, NULL); \
	if (hentry) \
		PORTAL = hentry->portal; \
	else \
		PORTAL = NULL; \
} while(0)

#define PortalHashTableInsert(PORTAL, NAME) \
do { \
	PortalHashEnt *hentry; bool found; \
	\
	hentry = (PortalHashEnt *) hash_search(PortalHashTable, \
										   (NAME), 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; \
	\
	hentry = (PortalHashEnt *) hash_search(PortalHashTable, \
										   PORTAL->name, 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;
}

/*
 * PortalListGetPrimaryStmt
 *		Get the "primary" stmt within a portal, ie, the one marked canSetTag.
 *
 * Returns NULL if no such stmt.  If multiple PlannedStmt structs within the
 * portal are marked canSetTag, returns the first one.	Neither of these
 * cases should occur in present usages of this function.
 *
 * Copes if given a list of Querys --- can't happen in a portal, but this
 * code also supports plancache.c, which needs both cases.
 *
 * Note: the reason this is just handed a List is so that plancache.c
 * can share the code.	For use with a portal, use PortalGetPrimaryStmt
 * rather than calling this directly.
 */
Node *
PortalListGetPrimaryStmt(List *stmts)
{
	ListCell   *lc;

	foreach(lc, stmts)
	{
		Node	   *stmt = (Node *) lfirst(lc);

		if (IsA(stmt, PlannedStmt))
		{
			if (((PlannedStmt *) stmt)->canSetTag)
				return stmt;
		}
		else if (IsA(stmt, Query))
		{
			if (((Query *) stmt)->canSetTag)
				return stmt;
		}
		else
		{
			/* Utility stmts are assumed canSetTag if they're the only stmt */
			if (list_length(stmts) == 1)
				return stmt;
		}
	}
	return NULL;
}

/*
 * 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->status = PORTAL_NEW;
	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 */
	portal->visible = true;
	portal->creation_time = GetCurrentStatementStartTimestamp();

	/* 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 %u>", 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.
 *
 * If cplan is provided, then it is a cached plan containing the stmts,
 * and the caller must have done RevalidateCachedPlan(), causing a refcount
 * increment.  The refcount will be released when the portal is destroyed.
 *
 * If cplan is NULL, then it is the caller's responsibility to ensure that
 * the passed plan trees have adequate lifetime.  Typically this is done by
 * copying them into the portal's heap context.
 *
 * The caller is also responsible for ensuring that the passed prepStmtName
 * and sourceText (if not NULL) have adequate lifetime.
 *
 * NB: this function mustn't do much beyond storing the passed values; in
 * particular don't do anything that risks elog(ERROR).  If that were to
 * happen here before storing the cplan reference, we'd leak the plancache
 * refcount that the caller is trying to hand off to us.
 */
void
PortalDefineQuery(Portal portal,
				  const char *prepStmtName,
				  const char *sourceText,
				  const char *commandTag,
				  List *stmts,
				  CachedPlan *cplan)
{
	AssertArg(PortalIsValid(portal));
	AssertState(portal->status == PORTAL_NEW);

	Assert(commandTag != NULL || stmts == NIL);

	portal->prepStmtName = prepStmtName;
	portal->sourceText = sourceText;
	portal->commandTag = commandTag;
	portal->stmts = stmts;
	portal->cplan = cplan;
	portal->status = PORTAL_DEFINED;
}

/*
 * PortalReleaseCachedPlan
 *		Release a portal's reference to its cached plan, if any.
 */
static void
PortalReleaseCachedPlan(Portal portal)
{
	if (portal->cplan)
	{
		ReleaseCachedPlan(portal->cplan, false);
		portal->cplan = NULL;
	}
}

/*
 * 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);

	/* drop cached plan reference, if any */
	if (portal->cplan)
		PortalReleaseCachedPlan(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);
}

/*
 * Delete all declared cursors.
 *
 * Used by commands: CLOSE ALL, DISCARD ALL
 */
void
PortalHashTableDeleteAll(void)
{
	HASH_SEQ_STATUS status;
	PortalHashEnt *hentry;

	if (PortalHashTable == NULL)
		return;

	hash_seq_init(&status, PortalHashTable);
	while ((hentry = hash_seq_search(&status)) != NULL)
	{
		Portal		portal = hentry->portal;

		if (portal->status != PORTAL_ACTIVE)
			PortalDrop(portal, false);
	}
}