execmain.c

PostgreSQL7.4.6 for Linux

/*-------------------------------------------------------------------------
 *
 * execMain.c
 *	  top level executor interface routines
 *
 * INTERFACE ROUTINES
 *	ExecutorStart()
 *	ExecutorRun()
 *	ExecutorEnd()
 *
 *	The old ExecutorMain() has been replaced by ExecutorStart(),
 *	ExecutorRun() and ExecutorEnd()
 *
 *	These three procedures are the external interfaces to the executor.
 *	In each case, the query descriptor is required as an argument.
 *
 *	ExecutorStart() must be called at the beginning of execution of any
 *	query plan and ExecutorEnd() should always be called at the end of
 *	execution of a plan.
 *
 *	ExecutorRun accepts direction and count arguments that specify whether
 *	the plan is to be executed forwards, backwards, and for how many tuples.
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/executor/execMain.c,v 1.220.2.2 2004/03/02 18:56:28 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "catalog/heap.h"
#include "catalog/namespace.h"
#include "commands/tablecmds.h"
#include "commands/trigger.h"
#include "executor/execdebug.h"
#include "executor/execdefs.h"
#include "miscadmin.h"
#include "optimizer/var.h"
#include "parser/parsetree.h"
#include "utils/acl.h"
#include "utils/lsyscache.h"


typedef struct execRowMark
{
	Relation	relation;
	Index		rti;
	char		resname[32];
} execRowMark;

typedef struct evalPlanQual
{
	Index		rti;
	EState	   *estate;
	PlanState  *planstate;
	struct evalPlanQual *next;	/* stack of active PlanQual plans */
	struct evalPlanQual *free;	/* list of free PlanQual plans */
} evalPlanQual;

/* decls for local routines only used within this module */
static void InitPlan(QueryDesc *queryDesc, bool explainOnly);
static void initResultRelInfo(ResultRelInfo *resultRelInfo,
				  Index resultRelationIndex,
				  List *rangeTable,
				  CmdType operation);
static TupleTableSlot *ExecutePlan(EState *estate, PlanState *planstate,
			CmdType operation,
			long numberTuples,
			ScanDirection direction,
			DestReceiver *dest);
static void ExecSelect(TupleTableSlot *slot,
		   DestReceiver *dest,
		   EState *estate);
static void ExecInsert(TupleTableSlot *slot, ItemPointer tupleid,
		   EState *estate);
static void ExecDelete(TupleTableSlot *slot, ItemPointer tupleid,
		   EState *estate);
static void ExecUpdate(TupleTableSlot *slot, ItemPointer tupleid,
		   EState *estate);
static TupleTableSlot *EvalPlanQualNext(EState *estate);
static void EndEvalPlanQual(EState *estate);
static void ExecCheckRTEPerms(RangeTblEntry *rte, CmdType operation);
static void ExecCheckXactReadOnly(Query *parsetree, CmdType operation);
static void EvalPlanQualStart(evalPlanQual *epq, EState *estate,
				  evalPlanQual *priorepq);
static void EvalPlanQualStop(evalPlanQual *epq);

/* end of local decls */


/* ----------------------------------------------------------------
 *		ExecutorStart
 *
 *		This routine must be called at the beginning of any execution of any
 *		query plan
 *
 * Takes a QueryDesc previously created by CreateQueryDesc (it's not real
 * clear why we bother to separate the two functions, but...).	The tupDesc
 * field of the QueryDesc is filled in to describe the tuples that will be
 * returned, and the internal fields (estate and planstate) are set up.
 *
 * If useCurrentSnapshot is true, run the query with the latest available
 * snapshot, instead of the normal QuerySnapshot.  Also, if it's an update
 * or delete query, check that the rows to be updated or deleted would be
 * visible to the normal QuerySnapshot.  (This is a special-case behavior
 * needed for referential integrity updates in serializable transactions.
 * We must check all currently-committed rows, but we want to throw a
 * can't-serialize error if any rows that would need updates would not be
 * visible under the normal serializable snapshot.)
 *
 * If explainOnly is true, we are not actually intending to run the plan,
 * only to set up for EXPLAIN; so skip unwanted side-effects.
 *
 * NB: the CurrentMemoryContext when this is called will become the parent
 * of the per-query context used for this Executor invocation.
 * ----------------------------------------------------------------
 */
void
ExecutorStart(QueryDesc *queryDesc, bool useCurrentSnapshot, bool explainOnly)
{
	EState	   *estate;
	MemoryContext oldcontext;

	/* sanity checks: queryDesc must not be started already */
	Assert(queryDesc != NULL);
	Assert(queryDesc->estate == NULL);

	/*
	 * If the transaction is read-only, we need to check if any writes are
	 * planned to non-temporary tables.
	 */
	if (!explainOnly)
		ExecCheckXactReadOnly(queryDesc->parsetree, queryDesc->operation);

	/*
	 * Build EState, switch into per-query memory context for startup.
	 */
	estate = CreateExecutorState();
	queryDesc->estate = estate;

	oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);

	/*
	 * Fill in parameters, if any, from queryDesc
	 */
	estate->es_param_list_info = queryDesc->params;

	if (queryDesc->plantree->nParamExec > 0)
		estate->es_param_exec_vals = (ParamExecData *)
			palloc0(queryDesc->plantree->nParamExec * sizeof(ParamExecData));

	estate->es_instrument = queryDesc->doInstrument;

	/*
	 * Make our own private copy of the current query snapshot data.
	 *
	 * This "freezes" our idea of which tuples are good and which are not for
	 * the life of this query, even if it outlives the current command and
	 * current snapshot.
	 */
	if (useCurrentSnapshot)
	{
		/* RI update/delete query --- must use an up-to-date snapshot */
		estate->es_snapshot = CopyCurrentSnapshot();
		/* crosscheck updates/deletes against transaction snapshot */
		estate->es_crosscheck_snapshot = CopyQuerySnapshot();
	}
	else
	{
		/* normal query --- use query snapshot, no crosscheck */
		estate->es_snapshot = CopyQuerySnapshot();
		estate->es_crosscheck_snapshot = SnapshotAny;
	}

	/*
	 * Initialize the plan state tree
	 */
	InitPlan(queryDesc, explainOnly);

	MemoryContextSwitchTo(oldcontext);
}

/* ----------------------------------------------------------------
 *		ExecutorRun
 *
 *		This is the main routine of the executor module. It accepts
 *		the query descriptor from the traffic cop and executes the
 *		query plan.
 *
 *		ExecutorStart must have been called already.
 *
 *		If direction is NoMovementScanDirection then nothing is done
 *		except to start up/shut down the destination.  Otherwise,
 *		we retrieve up to 'count' tuples in the specified direction.
 *
 *		Note: count = 0 is interpreted as no portal limit, i.e., run to
 *		completion.
 *
 * ----------------------------------------------------------------
 */
TupleTableSlot *
ExecutorRun(QueryDesc *queryDesc,
			ScanDirection direction, long count)
{
	EState	   *estate;
	CmdType		operation;
	DestReceiver *dest;
	TupleTableSlot *result;
	MemoryContext oldcontext;

	/* sanity checks */
	Assert(queryDesc != NULL);

	estate = queryDesc->estate;

	Assert(estate != NULL);

	/*
	 * Switch into per-query memory context
	 */
	oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);

	/*
	 * extract information from the query descriptor and the query
	 * feature.
	 */
	operation = queryDesc->operation;
	dest = queryDesc->dest;

	/*
	 * startup tuple receiver
	 */
	estate->es_processed = 0;
	estate->es_lastoid = InvalidOid;

	(*dest->rStartup) (dest, operation, queryDesc->tupDesc);

	/*
	 * run plan
	 */
	if (direction == NoMovementScanDirection)
		result = NULL;
	else
		result = ExecutePlan(estate,
							 queryDesc->planstate,
							 operation,
							 count,
							 direction,
							 dest);

	/*
	 * shutdown receiver
	 */
	(*dest->rShutdown) (dest);

	MemoryContextSwitchTo(oldcontext);

	return result;
}

/* ----------------------------------------------------------------
 *		ExecutorEnd
 *
 *		This routine must be called at the end of execution of any
 *		query plan
 * ----------------------------------------------------------------
 */
void
ExecutorEnd(QueryDesc *queryDesc)
{
	EState	   *estate;
	MemoryContext oldcontext;

	/* sanity checks */
	Assert(queryDesc != NULL);

	estate = queryDesc->estate;

	Assert(estate != NULL);

	/*
	 * Switch into per-query memory context to run ExecEndPlan
	 */
	oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);

	ExecEndPlan(queryDesc->planstate, estate);

	/*
	 * Must switch out of context before destroying it
	 */
	MemoryContextSwitchTo(oldcontext);

	/*
	 * Release EState and per-query memory context.  This should release
	 * everything the executor has allocated.
	 */
	FreeExecutorState(estate);

	/* Reset queryDesc fields that no longer point to anything */
	queryDesc->tupDesc = NULL;
	queryDesc->estate = NULL;
	queryDesc->planstate = NULL;
}

/* ----------------------------------------------------------------
 *		ExecutorRewind
 *
 *		This routine may be called on an open queryDesc to rewind it
 *		to the start.
 * ----------------------------------------------------------------
 */
void
ExecutorRewind(QueryDesc *queryDesc)
{
	EState	   *estate;
	MemoryContext oldcontext;

	/* sanity checks */
	Assert(queryDesc != NULL);

	estate = queryDesc->estate;

	Assert(estate != NULL);

	/* It's probably not sensible to rescan updating queries */
	Assert(queryDesc->operation == CMD_SELECT);

	/*
	 * Switch into per-query memory context
	 */
	oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);

	/*
	 * rescan plan
	 */
	ExecReScan(queryDesc->planstate, NULL);

	MemoryContextSwitchTo(oldcontext);
}


/*
 * ExecCheckRTPerms
 *		Check access permissions for all relations listed in a range table.
 */
void
ExecCheckRTPerms(List *rangeTable, CmdType operation)
{
	List	   *lp;

	foreach(lp, rangeTable)
	{
		RangeTblEntry *rte = lfirst(lp);

		ExecCheckRTEPerms(rte, operation);
	}
}

/*
 * ExecCheckRTEPerms
 *		Check access permissions for a single RTE.
 */
static void
ExecCheckRTEPerms(RangeTblEntry *rte, CmdType operation)
{
	Oid			relOid;
	AclId		userid;
	AclResult	aclcheck_result;

	/*
	 * If it's a subquery, recursively examine its rangetable.
	 */
	if (rte->rtekind == RTE_SUBQUERY)
	{
		ExecCheckRTPerms(rte->subquery->rtable, operation);
		return;
	}

	/*
	 * Otherwise, only plain-relation RTEs need to be checked here.
	 * Function RTEs are checked by init_fcache when the function is
	 * prepared for execution. Join and special RTEs need no checks.
	 */
	if (rte->rtekind != RTE_RELATION)
		return;

	relOid = rte->relid;

	/*
	 * userid to check as: current user unless we have a setuid
	 * indication.
	 *
	 * Note: GetUserId() is presently fast enough that there's no harm in
	 * calling it separately for each RTE.	If that stops being true, we
	 * could call it once in ExecCheckRTPerms and pass the userid down
	 * from there.	But for now, no need for the extra clutter.
	 */
	userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();

#define CHECK(MODE)		pg_class_aclcheck(relOid, userid, MODE)

	if (rte->checkForRead)
	{
		aclcheck_result = CHECK(ACL_SELECT);
		if (aclcheck_result != ACLCHECK_OK)
			aclcheck_error(aclcheck_result, ACL_KIND_CLASS,
						   get_rel_name(relOid));
	}

	if (rte->checkForWrite)
	{
		/*
		 * Note: write access in a SELECT context means SELECT FOR UPDATE.
		 * Right now we don't distinguish that from true update as far as
		 * permissions checks are concerned.
		 */
		switch (operation)
		{
			case CMD_INSERT:
				aclcheck_result = CHECK(ACL_INSERT);
				break;
			case CMD_SELECT:
			case CMD_UPDATE:
				aclcheck_result = CHECK(ACL_UPDATE);
				break;
			case CMD_DELETE:
				aclcheck_result = CHECK(ACL_DELETE);
				break;
			default:
				elog(ERROR, "unrecognized operation code: %d",
					 (int) operation);
				aclcheck_result = ACLCHECK_OK;	/* keep compiler quiet */
				break;
		}
		if (aclcheck_result != ACLCHECK_OK)
			aclcheck_error(aclcheck_result, ACL_KIND_CLASS,
						   get_rel_name(relOid));
	}
}

static void
ExecCheckXactReadOnly(Query *parsetree, CmdType operation)
{
	if (!XactReadOnly)
		return;

	/* CREATE TABLE AS or SELECT INTO */
	if (operation == CMD_SELECT && parsetree->into != NULL)
		goto fail;

	if (operation == CMD_DELETE || operation == CMD_INSERT
		|| operation == CMD_UPDATE)
	{
		List	   *lp;

		foreach(lp, parsetree->rtable)
		{
			RangeTblEntry *rte = lfirst(lp);

			if (rte->rtekind != RTE_RELATION)
				continue;

			if (!rte->checkForWrite)
				continue;

			if (isTempNamespace(get_rel_namespace(rte->relid)))
				continue;

			goto fail;
		}
	}

	return;

fail:
	ereport(ERROR,
			(errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
			 errmsg("transaction is read-only")));
}


/* ----------------------------------------------------------------
 *		InitPlan
 *
 *		Initializes the query plan: open files, allocate storage
 *		and start up the rule manager
 * ----------------------------------------------------------------
 */
static void
InitPlan(QueryDesc *queryDesc, bool explainOnly)
{
	CmdType		operation = queryDesc->operation;
	Query	   *parseTree = queryDesc->parsetree;
	Plan	   *plan = queryDesc->plantree;
	EState	   *estate = queryDesc->estate;
	PlanState  *planstate;
	List	   *rangeTable;
	Relation	intoRelationDesc;
	bool		do_select_into;
	TupleDesc	tupType;

	/*
	 * Do permissions checks.  It's sufficient to examine the query's top
	 * rangetable here --- subplan RTEs will be checked during
	 * ExecInitSubPlan().
	 */
	ExecCheckRTPerms(parseTree->rtable, operation);

	/*
	 * get information from query descriptor
	 */
	rangeTable = parseTree->rtable;

	/*
	 * initialize the node's execution state
	 */
	estate->es_range_table = rangeTable;

	/*
	 * if there is a result relation, initialize result relation stuff
	 */
	if (parseTree->resultRelation != 0 && operation != CMD_SELECT)
	{
		List	   *resultRelations = parseTree->resultRelations;
		int			numResultRelations;
		ResultRelInfo *resultRelInfos;

		if (resultRelations != NIL)
		{
			/*
			 * Multiple result relations (due to inheritance)
			 * parseTree->resultRelations identifies them all
			 */
			ResultRelInfo *resultRelInfo;

			numResultRelations = length(resultRelations);
			resultRelInfos = (ResultRelInfo *)
				palloc(numResultRelations * sizeof(ResultRelInfo));
			resultRelInfo = resultRelInfos;