postgresql/src/backend/executor/execAmi.c

/*-------------------------------------------------------------------------
 *
 * execAmi.c
 *	  miscellaneous executor access method routines
 *
 * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *	$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.108 2010/02/14 18:42:14 rhaas Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "executor/execdebug.h"
#include "executor/instrument.h"
#include "executor/nodeAgg.h"
#include "executor/nodeAppend.h"
#include "executor/nodeBitmapAnd.h"
#include "executor/nodeBitmapHeapscan.h"
#include "executor/nodeBitmapIndexscan.h"
#include "executor/nodeBitmapOr.h"
#include "executor/nodeCtescan.h"
#include "executor/nodeFunctionscan.h"
#include "executor/nodeGroup.h"
#include "executor/nodeGroup.h"
#include "executor/nodeHash.h"
#include "executor/nodeHashjoin.h"
#include "executor/nodeIndexscan.h"
#include "executor/nodeLimit.h"
#include "executor/nodeLockRows.h"
#include "executor/nodeMaterial.h"
#include "executor/nodeMergejoin.h"
#include "executor/nodeModifyTable.h"
#include "executor/nodeNestloop.h"
#include "executor/nodeRecursiveunion.h"
#include "executor/nodeResult.h"
#include "executor/nodeSeqscan.h"
#include "executor/nodeSetOp.h"
#include "executor/nodeSort.h"
#include "executor/nodeSubplan.h"
#include "executor/nodeSubqueryscan.h"
#include "executor/nodeTidscan.h"
#include "executor/nodeUnique.h"
#include "executor/nodeValuesscan.h"
#include "executor/nodeWindowAgg.h"
#include "executor/nodeWorktablescan.h"
#include "nodes/nodeFuncs.h"
#include "utils/syscache.h"


static bool TargetListSupportsBackwardScan(List *targetlist);
static bool IndexSupportsBackwardScan(Oid indexid);


/*
 * ExecReScan
 *		Reset a plan node so that its output can be re-scanned.
 *
 * Note that if the plan node has parameters that have changed value,
 * the output might be different from last time.
 *
 * The second parameter is currently only used to pass a NestLoop plan's
 * econtext down to its inner child plan, in case that is an indexscan that
 * needs access to variables of the current outer tuple.  (The handling of
 * this parameter is currently pretty inconsistent: some callers pass NULL
 * and some pass down their parent's value; so don't rely on it in other
 * situations.	It'd probably be better to remove the whole thing and use
 * the generalized parameter mechanism instead.)
 */
void
ExecReScan(PlanState *node, ExprContext *exprCtxt)
{
	/* If collecting timing stats, update them */
	if (node->instrument)
		InstrEndLoop(node->instrument);

	/*
	 * If we have changed parameters, propagate that info.
	 *
	 * Note: ExecReScanSetParamPlan() can add bits to node->chgParam,
	 * corresponding to the output param(s) that the InitPlan will update.
	 * Since we make only one pass over the list, that means that an InitPlan
	 * can depend on the output param(s) of a sibling InitPlan only if that
	 * sibling appears earlier in the list.  This is workable for now given
	 * the limited ways in which one InitPlan could depend on another, but
	 * eventually we might need to work harder (or else make the planner
	 * enlarge the extParam/allParam sets to include the params of depended-on
	 * InitPlans).
	 */
	if (node->chgParam != NULL)
	{
		ListCell   *l;

		foreach(l, node->initPlan)
		{
			SubPlanState *sstate = (SubPlanState *) lfirst(l);
			PlanState  *splan = sstate->planstate;

			if (splan->plan->extParam != NULL)	/* don't care about child
												 * local Params */
				UpdateChangedParamSet(splan, node->chgParam);
			if (splan->chgParam != NULL)
				ExecReScanSetParamPlan(sstate, node);
		}
		foreach(l, node->subPlan)
		{
			SubPlanState *sstate = (SubPlanState *) lfirst(l);
			PlanState  *splan = sstate->planstate;

			if (splan->plan->extParam != NULL)
				UpdateChangedParamSet(splan, node->chgParam);
		}
		/* Well. Now set chgParam for left/right trees. */
		if (node->lefttree != NULL)
			UpdateChangedParamSet(node->lefttree, node->chgParam);
		if (node->righttree != NULL)
			UpdateChangedParamSet(node->righttree, node->chgParam);
	}

	/* Shut down any SRFs in the plan node's targetlist */
	if (node->ps_ExprContext)
		ReScanExprContext(node->ps_ExprContext);

	/* And do node-type-specific processing */
	switch (nodeTag(node))
	{
		case T_ResultState:
			ExecReScanResult((ResultState *) node, exprCtxt);
			break;

		case T_ModifyTableState:
			ExecReScanModifyTable((ModifyTableState *) node, exprCtxt);
			break;

		case T_AppendState:
			ExecReScanAppend((AppendState *) node, exprCtxt);
			break;

		case T_RecursiveUnionState:
			ExecRecursiveUnionReScan((RecursiveUnionState *) node, exprCtxt);
			break;

		case T_BitmapAndState:
			ExecReScanBitmapAnd((BitmapAndState *) node, exprCtxt);
			break;

		case T_BitmapOrState:
			ExecReScanBitmapOr((BitmapOrState *) node, exprCtxt);
			break;

		case T_SeqScanState:
			ExecSeqReScan((SeqScanState *) node, exprCtxt);
			break;

		case T_IndexScanState:
			ExecIndexReScan((IndexScanState *) node, exprCtxt);
			break;

		case T_BitmapIndexScanState:
			ExecBitmapIndexReScan((BitmapIndexScanState *) node, exprCtxt);
			break;

		case T_BitmapHeapScanState:
			ExecBitmapHeapReScan((BitmapHeapScanState *) node, exprCtxt);
			break;

		case T_TidScanState:
			ExecTidReScan((TidScanState *) node, exprCtxt);
			break;

		case T_SubqueryScanState:
			ExecSubqueryReScan((SubqueryScanState *) node, exprCtxt);
			break;

		case T_FunctionScanState:
			ExecFunctionReScan((FunctionScanState *) node, exprCtxt);
			break;

		case T_ValuesScanState:
			ExecValuesReScan((ValuesScanState *) node, exprCtxt);
			break;

		case T_CteScanState:
			ExecCteScanReScan((CteScanState *) node, exprCtxt);
			break;

		case T_WorkTableScanState:
			ExecWorkTableScanReScan((WorkTableScanState *) node, exprCtxt);
			break;

		case T_NestLoopState:
			ExecReScanNestLoop((NestLoopState *) node, exprCtxt);
			break;

		case T_MergeJoinState:
			ExecReScanMergeJoin((MergeJoinState *) node, exprCtxt);
			break;

		case T_HashJoinState:
			ExecReScanHashJoin((HashJoinState *) node, exprCtxt);
			break;

		case T_MaterialState:
			ExecMaterialReScan((MaterialState *) node, exprCtxt);
			break;

		case T_SortState:
			ExecReScanSort((SortState *) node, exprCtxt);
			break;

		case T_GroupState:
			ExecReScanGroup((GroupState *) node, exprCtxt);
			break;

		case T_AggState:
			ExecReScanAgg((AggState *) node, exprCtxt);
			break;

		case T_WindowAggState:
			ExecReScanWindowAgg((WindowAggState *) node, exprCtxt);
			break;

		case T_UniqueState:
			ExecReScanUnique((UniqueState *) node, exprCtxt);
			break;

		case T_HashState:
			ExecReScanHash((HashState *) node, exprCtxt);
			break;

		case T_SetOpState:
			ExecReScanSetOp((SetOpState *) node, exprCtxt);
			break;

		case T_LockRowsState:
			ExecReScanLockRows((LockRowsState *) node, exprCtxt);
			break;

		case T_LimitState:
			ExecReScanLimit((LimitState *) node, exprCtxt);
			break;

		default:
			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
			break;
	}

	if (node->chgParam != NULL)
	{
		bms_free(node->chgParam);
		node->chgParam = NULL;
	}
}

/*
 * ExecMarkPos
 *
 * Marks the current scan position.
 */
void
ExecMarkPos(PlanState *node)
{
	switch (nodeTag(node))
	{
		case T_SeqScanState:
			ExecSeqMarkPos((SeqScanState *) node);
			break;

		case T_IndexScanState:
			ExecIndexMarkPos((IndexScanState *) node);
			break;

		case T_TidScanState:
			ExecTidMarkPos((TidScanState *) node);
			break;

		case T_ValuesScanState:
			ExecValuesMarkPos((ValuesScanState *) node);
			break;

		case T_MaterialState:
			ExecMaterialMarkPos((MaterialState *) node);
			break;

		case T_SortState:
			ExecSortMarkPos((SortState *) node);
			break;

		case T_ResultState:
			ExecResultMarkPos((ResultState *) node);
			break;

		default:
			/* don't make hard error unless caller asks to restore... */
			elog(DEBUG2, "unrecognized node type: %d", (int) nodeTag(node));
			break;
	}
}

/*
 * ExecRestrPos
 *
 * restores the scan position previously saved with ExecMarkPos()
 *
 * NOTE: the semantics of this are that the first ExecProcNode following
 * the restore operation will yield the same tuple as the first one following
 * the mark operation.	It is unspecified what happens to the plan node's
 * result TupleTableSlot.  (In most cases the result slot is unchanged by
 * a restore, but the node may choose to clear it or to load it with the
 * restored-to tuple.)	Hence the caller should discard any previously
 * returned TupleTableSlot after doing a restore.
 */
void
ExecRestrPos(PlanState *node)
{
	switch (nodeTag(node))
	{
		case T_SeqScanState:
			ExecSeqRestrPos((SeqScanState *) node);
			break;

		case T_IndexScanState:
			ExecIndexRestrPos((IndexScanState *) node);
			break;

		case T_TidScanState:
			ExecTidRestrPos((TidScanState *) node);
			break;

		case T_ValuesScanState:
			ExecValuesRestrPos((ValuesScanState *) node);
			break;

		case T_MaterialState:
			ExecMaterialRestrPos((MaterialState *) node);
			break;

		case T_SortState:
			ExecSortRestrPos((SortState *) node);
			break;

		case T_ResultState:
			ExecResultRestrPos((ResultState *) node);
			break;

		default:
			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
			break;
	}
}

/*
 * ExecSupportsMarkRestore - does a plan type support mark/restore?
 *
 * XXX Ideally, all plan node types would support mark/restore, and this
 * wouldn't be needed.  For now, this had better match the routines above.
 * But note the test is on Plan nodetype, not PlanState nodetype.
 *
 * (However, since the only present use of mark/restore is in mergejoin,
 * there is no need to support mark/restore in any plan type that is not
 * capable of generating ordered output.  So the seqscan, tidscan,
 * and valuesscan support is actually useless code at present.)
 */
bool
ExecSupportsMarkRestore(NodeTag plantype)
{
	switch (plantype)
	{
		case T_SeqScan:
		case T_IndexScan:
		case T_TidScan:
		case T_ValuesScan:
		case T_Material:
		case T_Sort:
			return true;

		case T_Result:

			/*
			 * T_Result only supports mark/restore if it has a child plan that
			 * does, so we do not have enough information to give a really
			 * correct answer.	However, for current uses it's enough to
			 * always say "false", because this routine is not asked about
			 * gating Result plans, only base-case Results.
			 */
			return false;

		default:
			break;
	}

	return false;
}

/*
 * ExecSupportsBackwardScan - does a plan type support backwards scanning?
 *
 * Ideally, all plan types would support backwards scan, but that seems
 * unlikely to happen soon.  In some cases, a plan node passes the backwards
 * scan down to its children, and so supports backwards scan only if its
 * children do.  Therefore, this routine must be passed a complete plan tree.
 */
bool
ExecSupportsBackwardScan(Plan *node)
{
	if (node == NULL)
		return false;

	switch (nodeTag(node))
	{
		case T_Result:
			if (outerPlan(node) != NULL)
				return ExecSupportsBackwardScan(outerPlan(node)) &&
					TargetListSupportsBackwardScan(node->targetlist);
			else
				return false;

		case T_Append:
			{
				ListCell   *l;

				foreach(l, ((Append *) node)->appendplans)
				{
					if (!ExecSupportsBackwardScan((Plan *) lfirst(l)))
						return false;
				}
				/* need not check tlist because Append doesn't evaluate it */
				return true;
			}

		case T_SeqScan:
		case T_TidScan:
		case T_FunctionScan:
		case T_ValuesScan:
		case T_CteScan:
			return TargetListSupportsBackwardScan(node->targetlist);

		case T_IndexScan:
			return IndexSupportsBackwardScan(((IndexScan *) node)->indexid) &&
				TargetListSupportsBackwardScan(node->targetlist);

		case T_SubqueryScan:
			return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan) &&
				TargetListSupportsBackwardScan(node->targetlist);

		case T_Material:
		case T_Sort:
			/* these don't evaluate tlist */
			return true;

		case T_LockRows:
		case T_Limit:
			/* these don't evaluate tlist */
			return ExecSupportsBackwardScan(outerPlan(node));

		default:
			return false;
	}
}

/*
 * If the tlist contains set-returning functions, we can't support backward
 * scan, because the TupFromTlist code is direction-ignorant.
 */
static bool
TargetListSupportsBackwardScan(List *targetlist)
{
	if (expression_returns_set((Node *) targetlist))
		return false;
	return true;
}

/*
 * An IndexScan node supports backward scan only if the index's AM does.
 */
static bool
IndexSupportsBackwardScan(Oid indexid)
{
	bool		result;
	HeapTuple	ht_idxrel;
	HeapTuple	ht_am;
	Form_pg_class idxrelrec;
	Form_pg_am	amrec;

	/* Fetch the pg_class tuple of the index relation */
	ht_idxrel = SearchSysCache1(RELOID, ObjectIdGetDatum(indexid));
	if (!HeapTupleIsValid(ht_idxrel))
		elog(ERROR, "cache lookup failed for relation %u", indexid);
	idxrelrec = (Form_pg_class) GETSTRUCT(ht_idxrel);

	/* Fetch the pg_am tuple of the index' access method */
	ht_am = SearchSysCache1(AMOID, ObjectIdGetDatum(idxrelrec->relam));
	if (!HeapTupleIsValid(ht_am))
		elog(ERROR, "cache lookup failed for access method %u",
			 idxrelrec->relam);
	amrec = (Form_pg_am) GETSTRUCT(ht_am);

	result = amrec->amcanbackward;

	ReleaseSysCache(ht_idxrel);
	ReleaseSysCache(ht_am);

	return result;
}

/*
 * ExecMaterializesOutput - does a plan type materialize its output?
 *
 * Returns true if the plan node type is one that automatically materializes
 * its output (typically by keeping it in a tuplestore).  For such plans,
 * a rescan without any parameter change will have zero startup cost and
 * very low per-tuple cost.
 */
bool
ExecMaterializesOutput(NodeTag plantype)
{
	switch (plantype)
	{
		case T_Material:
		case T_FunctionScan:
		case T_CteScan:
		case T_WorkTableScan:
		case T_Sort:
			return true;

		default:
			break;
	}

	return false;
}