postgres/src/backend/executor/nodeMaterial.c

/*-------------------------------------------------------------------------
 *
 * nodeMaterial.c
 *	  Routines to handle materialization nodes.
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/executor/nodeMaterial.c,v 1.46 2004/02/03 17:34:02 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *		ExecMaterial			- materialize the result of a subplan
 *		ExecInitMaterial		- initialize node and subnodes
 *		ExecEndMaterial			- shutdown node and subnodes
 *
 */
#include "postgres.h"

#include "access/heapam.h"
#include "executor/executor.h"
#include "executor/nodeMaterial.h"
#include "miscadmin.h"
#include "utils/tuplestore.h"

/* ----------------------------------------------------------------
 *		ExecMaterial
 *
 *		As long as we are at the end of the data collected in the tuplestore,
 *		we collect one new row from the subplan on each call, and stash it
 *		aside in the tuplestore before returning it.  The tuplestore is
 *		only read if we are asked to scan backwards, rescan, or mark/restore.
 *
 * ----------------------------------------------------------------
 */
TupleTableSlot *				/* result tuple from subplan */
ExecMaterial(MaterialState *node)
{
	EState	   *estate;
	ScanDirection dir;
	bool		forward;
	Tuplestorestate *tuplestorestate;
	HeapTuple	heapTuple = NULL;
	bool		should_free = false;
	bool		eof_tuplestore;
	TupleTableSlot *slot;

	/*
	 * get state info from node
	 */
	estate = node->ss.ps.state;
	dir = estate->es_direction;
	forward = ScanDirectionIsForward(dir);
	tuplestorestate = (Tuplestorestate *) node->tuplestorestate;

	/*
	 * If first time through, initialize the tuplestore.
	 */
	if (tuplestorestate == NULL)
	{
		tuplestorestate = tuplestore_begin_heap(true, false, work_mem);

		node->tuplestorestate = (void *) tuplestorestate;
	}

	/*
	 * If we are not at the end of the tuplestore, or are going backwards,
	 * try to fetch a tuple from tuplestore.
	 */
	eof_tuplestore = tuplestore_ateof(tuplestorestate);

	if (!forward && eof_tuplestore)
	{
		if (!node->eof_underlying)
		{
			/*
			 * When reversing direction at tuplestore EOF, the first
			 * getheaptuple call will fetch the last-added tuple; but we
			 * want to return the one before that, if possible. So do an
			 * extra fetch.
			 */
			heapTuple = tuplestore_getheaptuple(tuplestorestate,
												forward,
												&should_free);
			if (heapTuple == NULL)
				return NULL;	/* the tuplestore must be empty */
			if (should_free)
				heap_freetuple(heapTuple);
		}
		eof_tuplestore = false;
	}

	if (!eof_tuplestore)
	{
		heapTuple = tuplestore_getheaptuple(tuplestorestate,
											forward,
											&should_free);
		if (heapTuple == NULL && forward)
			eof_tuplestore = true;
	}

	/*
	 * If necessary, try to fetch another row from the subplan.
	 *
	 * Note: the eof_underlying state variable exists to short-circuit
	 * further subplan calls.  It's not optional, unfortunately, because
	 * some plan node types are not robust about being called again when
	 * they've already returned NULL.
	 */
	if (eof_tuplestore && !node->eof_underlying)
	{
		PlanState  *outerNode;
		TupleTableSlot *outerslot;

		/*
		 * We can only get here with forward==true, so no need to worry
		 * about which direction the subplan will go.
		 */
		outerNode = outerPlanState(node);
		outerslot = ExecProcNode(outerNode);
		if (TupIsNull(outerslot))
		{
			node->eof_underlying = true;
			return NULL;
		}
		heapTuple = outerslot->val;
		should_free = false;

		/*
		 * Append returned tuple to tuplestore, too.  NOTE: because the
		 * tuplestore is certainly in EOF state, its read position will
		 * move forward over the added tuple.  This is what we want.
		 */
		tuplestore_puttuple(tuplestorestate, (void *) heapTuple);
	}

	/*
	 * Return the obtained tuple.
	 */
	slot = (TupleTableSlot *) node->ss.ps.ps_ResultTupleSlot;
	return ExecStoreTuple(heapTuple, slot, InvalidBuffer, should_free);
}

/* ----------------------------------------------------------------
 *		ExecInitMaterial
 * ----------------------------------------------------------------
 */
MaterialState *
ExecInitMaterial(Material *node, EState *estate)
{
	MaterialState *matstate;
	Plan	   *outerPlan;

	/*
	 * create state structure
	 */
	matstate = makeNode(MaterialState);
	matstate->ss.ps.plan = (Plan *) node;
	matstate->ss.ps.state = estate;

	matstate->tuplestorestate = NULL;
	matstate->eof_underlying = false;

	/*
	 * Miscellaneous initialization
	 *
	 * Materialization nodes don't need ExprContexts because they never call
	 * ExecQual or ExecProject.
	 */

#define MATERIAL_NSLOTS 2

	/*
	 * tuple table initialization
	 *
	 * material nodes only return tuples from their materialized relation.
	 */
	ExecInitResultTupleSlot(estate, &matstate->ss.ps);
	ExecInitScanTupleSlot(estate, &matstate->ss);

	/*
	 * initializes child nodes
	 */
	outerPlan = outerPlan(node);
	outerPlanState(matstate) = ExecInitNode(outerPlan, estate);

	/*
	 * initialize tuple type.  no need to initialize projection info
	 * because this node doesn't do projections.
	 */
	ExecAssignResultTypeFromOuterPlan(&matstate->ss.ps);
	ExecAssignScanTypeFromOuterPlan(&matstate->ss);
	matstate->ss.ps.ps_ProjInfo = NULL;

	return matstate;
}

int
ExecCountSlotsMaterial(Material *node)
{
	return ExecCountSlotsNode(outerPlan((Plan *) node)) +
		ExecCountSlotsNode(innerPlan((Plan *) node)) +
		MATERIAL_NSLOTS;
}

/* ----------------------------------------------------------------
 *		ExecEndMaterial
 * ----------------------------------------------------------------
 */
void
ExecEndMaterial(MaterialState *node)
{
	/*
	 * clean out the tuple table
	 */
	ExecClearTuple(node->ss.ss_ScanTupleSlot);

	/*
	 * Release tuplestore resources
	 */
	if (node->tuplestorestate != NULL)
		tuplestore_end((Tuplestorestate *) node->tuplestorestate);
	node->tuplestorestate = NULL;

	/*
	 * shut down the subplan
	 */
	ExecEndNode(outerPlanState(node));
}

/* ----------------------------------------------------------------
 *		ExecMaterialMarkPos
 *
 *		Calls tuplestore to save the current position in the stored file.
 * ----------------------------------------------------------------
 */
void
ExecMaterialMarkPos(MaterialState *node)
{
	/*
	 * if we haven't materialized yet, just return.
	 */
	if (!node->tuplestorestate)
		return;

	tuplestore_markpos((Tuplestorestate *) node->tuplestorestate);
}

/* ----------------------------------------------------------------
 *		ExecMaterialRestrPos
 *
 *		Calls tuplestore to restore the last saved file position.
 * ----------------------------------------------------------------
 */
void
ExecMaterialRestrPos(MaterialState *node)
{
	/*
	 * if we haven't materialized yet, just return.
	 */
	if (!node->tuplestorestate)
		return;

	/*
	 * restore the scan to the previously marked position
	 */
	tuplestore_restorepos((Tuplestorestate *) node->tuplestorestate);
}

/* ----------------------------------------------------------------
 *		ExecMaterialReScan
 *
 *		Rescans the materialized relation.
 * ----------------------------------------------------------------
 */
void
ExecMaterialReScan(MaterialState *node, ExprContext *exprCtxt)
{
	/*
	 * If we haven't materialized yet, just return. If outerplan' chgParam
	 * is not NULL then it will be re-scanned by ExecProcNode, else - no
	 * reason to re-scan it at all.
	 */
	if (!node->tuplestorestate)
		return;

	ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);

	/*
	 * If subnode is to be rescanned then we forget previous stored
	 * results; we have to re-read the subplan and re-store.
	 *
	 * Otherwise we can just rewind and rescan the stored output. The state
	 * of the subnode does not change.
	 */
	if (((PlanState *) node)->lefttree->chgParam != NULL)
	{
		tuplestore_end((Tuplestorestate *) node->tuplestorestate);
		node->tuplestorestate = NULL;
		node->eof_underlying = false;
	}
	else
		tuplestore_rescan((Tuplestorestate *) node->tuplestorestate);
}