nodeindexscan.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

/*-------------------------------------------------------------------------
 *
 * nodeIndexscan.c
 *	  Routines to support indexed scans of relations
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.104.2.1 2005/11/22 18:23:09 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *		ExecIndexScan			scans a relation using indices
 *		ExecIndexNext			using index to retrieve next tuple
 *		ExecInitIndexScan		creates and initializes state info.
 *		ExecIndexReScan			rescans the indexed relation.
 *		ExecEndIndexScan		releases all storage.
 *		ExecIndexMarkPos		marks scan position.
 *		ExecIndexRestrPos		restores scan position.
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "executor/execdebug.h"
#include "executor/nodeIndexscan.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "parser/parsetree.h"
#include "utils/memutils.h"


static TupleTableSlot *IndexNext(IndexScanState *node);


/* ----------------------------------------------------------------
 *		IndexNext
 *
 *		Retrieve a tuple from the IndexScan node's currentRelation
 *		using the index specified in the IndexScanState information.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
IndexNext(IndexScanState *node)
{
	EState	   *estate;
	ExprContext *econtext;
	ScanDirection direction;
	IndexScanDesc scandesc;
	Index		scanrelid;
	HeapTuple	tuple;
	TupleTableSlot *slot;

	/*
	 * extract necessary information from index scan node
	 */
	estate = node->ss.ps.state;
	direction = estate->es_direction;
	/* flip direction if this is an overall backward scan */
	if (ScanDirectionIsBackward(((IndexScan *) node->ss.ps.plan)->indexorderdir))
	{
		if (ScanDirectionIsForward(direction))
			direction = BackwardScanDirection;
		else if (ScanDirectionIsBackward(direction))
			direction = ForwardScanDirection;
	}
	scandesc = node->iss_ScanDesc;
	econtext = node->ss.ps.ps_ExprContext;
	slot = node->ss.ss_ScanTupleSlot;
	scanrelid = ((IndexScan *) node->ss.ps.plan)->scan.scanrelid;

	/*
	 * Clear any reference to the previously returned tuple.  The idea here is
	 * to not have the tuple slot be the last holder of a pin on that tuple's
	 * buffer; if it is, we'll need a separate visit to the bufmgr to release
	 * the buffer.	By clearing here, we get to have the release done by
	 * ReleaseAndReadBuffer inside index_getnext.
	 */
	ExecClearTuple(slot);

	/*
	 * Check if we are evaluating PlanQual for tuple of this relation.
	 * Additional checking is not good, but no other way for now. We could
	 * introduce new nodes for this case and handle IndexScan --> NewNode
	 * switching in Init/ReScan plan...
	 */
	if (estate->es_evTuple != NULL &&
		estate->es_evTuple[scanrelid - 1] != NULL)
	{
		if (estate->es_evTupleNull[scanrelid - 1])
			return slot;		/* return empty slot */

		ExecStoreTuple(estate->es_evTuple[scanrelid - 1],
					   slot, InvalidBuffer, false);

		/* Does the tuple meet the indexqual condition? */
		econtext->ecxt_scantuple = slot;

		ResetExprContext(econtext);

		if (!ExecQual(node->indexqualorig, econtext, false))
			ExecClearTuple(slot);		/* would not be returned by scan */

		/* Flag for the next call that no more tuples */
		estate->es_evTupleNull[scanrelid - 1] = true;

		return slot;
	}

	/*
	 * ok, now that we have what we need, fetch the next tuple.
	 */
	if ((tuple = index_getnext(scandesc, direction)) != NULL)
	{
		/*
		 * Store the scanned tuple in the scan tuple slot of the scan state.
		 * Note: we pass 'false' because tuples returned by amgetnext are
		 * pointers onto disk pages and must not be pfree()'d.
		 */
		ExecStoreTuple(tuple,	/* tuple to store */
					   slot,	/* slot to store in */
					   scandesc->xs_cbuf,		/* buffer containing tuple */
					   false);	/* don't pfree */

		return slot;
	}

	/*
	 * if we get here it means the index scan failed so we are at the end of
	 * the scan..
	 */
	return ExecClearTuple(slot);
}

/* ----------------------------------------------------------------
 *		ExecIndexScan(node)
 * ----------------------------------------------------------------
 */
TupleTableSlot *
ExecIndexScan(IndexScanState *node)
{
	/*
	 * If we have runtime keys and they've not already been set up, do it now.
	 */
	if (node->iss_RuntimeKeyInfo && !node->iss_RuntimeKeysReady)
		ExecReScan((PlanState *) node, NULL);

	/*
	 * use IndexNext as access method
	 */
	return ExecScan(&node->ss, (ExecScanAccessMtd) IndexNext);
}

/* ----------------------------------------------------------------
 *		ExecIndexReScan(node)
 *
 *		Recalculates the value of the scan keys whose value depends on
 *		information known at runtime and rescans the indexed relation.
 *		Updating the scan key was formerly done separately in
 *		ExecUpdateIndexScanKeys. Integrating it into ReScan makes
 *		rescans of indices and relations/general streams more uniform.
 * ----------------------------------------------------------------
 */
void
ExecIndexReScan(IndexScanState *node, ExprContext *exprCtxt)
{
	EState	   *estate;
	ExprContext *econtext;
	ScanKey		scanKeys;
	ExprState **runtimeKeyInfo;
	int			numScanKeys;
	Index		scanrelid;

	estate = node->ss.ps.state;
	econtext = node->iss_RuntimeContext;		/* context for runtime keys */
	scanKeys = node->iss_ScanKeys;
	runtimeKeyInfo = node->iss_RuntimeKeyInfo;
	numScanKeys = node->iss_NumScanKeys;
	scanrelid = ((IndexScan *) node->ss.ps.plan)->scan.scanrelid;

	if (econtext)
	{
		/*
		 * If we are being passed an outer tuple, save it for runtime key
		 * calc.  We also need to link it into the "regular" per-tuple
		 * econtext, so it can be used during indexqualorig evaluations.
		 */
		if (exprCtxt != NULL)
		{
			ExprContext *stdecontext;

			econtext->ecxt_outertuple = exprCtxt->ecxt_outertuple;
			stdecontext = node->ss.ps.ps_ExprContext;
			stdecontext->ecxt_outertuple = exprCtxt->ecxt_outertuple;
		}

		/*
		 * Reset the runtime-key context so we don't leak memory as each outer
		 * tuple is scanned.  Note this assumes that we will recalculate *all*
		 * runtime keys on each call.
		 */
		ResetExprContext(econtext);
	}

	/*
	 * If we are doing runtime key calculations (ie, the index keys depend on
	 * data from an outer scan), compute the new key values
	 */
	if (runtimeKeyInfo)
	{
		ExecIndexEvalRuntimeKeys(econtext,
								 runtimeKeyInfo,
								 scanKeys,
								 numScanKeys);
		node->iss_RuntimeKeysReady = true;
	}

	/* If this is re-scanning of PlanQual ... */
	if (estate->es_evTuple != NULL &&
		estate->es_evTuple[scanrelid - 1] != NULL)
	{
		estate->es_evTupleNull[scanrelid - 1] = false;
		return;
	}

	/* reset index scan */
	index_rescan(node->iss_ScanDesc, scanKeys);
}


/*
 * ExecIndexEvalRuntimeKeys
 *		Evaluate any runtime key values, and update the scankeys.
 */
void
ExecIndexEvalRuntimeKeys(ExprContext *econtext,
						 ExprState **run_keys,
						 ScanKey scan_keys,
						 int n_keys)
{
	int			j;

	for (j = 0; j < n_keys; j++)
	{
		/*
		 * If we have a run-time key, then extract the run-time expression and
		 * evaluate it with respect to the current outer tuple.  We then stick
		 * the result into the scan key.
		 *
		 * Note: the result of the eval could be a pass-by-ref value that's
		 * stored in the outer scan's tuple, not in
		 * econtext->ecxt_per_tuple_memory.  We assume that the outer tuple
		 * will stay put throughout our scan.  If this is wrong, we could copy
		 * the result into our context explicitly, but I think that's not
		 * necessary...
		 */
		if (run_keys[j] != NULL)
		{
			Datum		scanvalue;
			bool		isNull;

			scanvalue = ExecEvalExprSwitchContext(run_keys[j],
												  econtext,
												  &isNull,
												  NULL);
			scan_keys[j].sk_argument = scanvalue;
			if (isNull)
				scan_keys[j].sk_flags |= SK_ISNULL;
			else
				scan_keys[j].sk_flags &= ~SK_ISNULL;
		}
	}
}

/* ----------------------------------------------------------------
 *		ExecEndIndexScan
 * ----------------------------------------------------------------
 */
void
ExecEndIndexScan(IndexScanState *node)
{
	Relation	indexRelationDesc;
	IndexScanDesc indexScanDesc;
	Relation	relation;

	/*
	 * extract information from the node
	 */
	indexRelationDesc = node->iss_RelationDesc;
	indexScanDesc = node->iss_ScanDesc;
	relation = node->ss.ss_currentRelation;

	/*
	 * Free the exprcontext(s) ... now dead code, see ExecFreeExprContext
	 */
#ifdef NOT_USED
	ExecFreeExprContext(&node->ss.ps);
	if (node->iss_RuntimeContext)
		FreeExprContext(node->iss_RuntimeContext);
#endif

	/*
	 * clear out tuple table slots
	 */
	ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
	ExecClearTuple(node->ss.ss_ScanTupleSlot);

	/*
	 * close the index relation
	 */
	index_endscan(indexScanDesc);
	index_close(indexRelationDesc);

	/*
	 * close the heap relation.
	 *
	 * Currently, we do not release the AccessShareLock acquired by
	 * ExecInitIndexScan.  This lock should be held till end of transaction.
	 * (There is a faction that considers this too much locking, however.)
	 */
	heap_close(relation, NoLock);
}

/* ----------------------------------------------------------------
 *		ExecIndexMarkPos
 * ----------------------------------------------------------------
 */
void
ExecIndexMarkPos(IndexScanState *node)
{
	index_markpos(node->iss_ScanDesc);