postgres/src/backend/executor/nodeNestloop.c

/*-------------------------------------------------------------------------
 *
 * nodeNestloop.c
 *	  routines to support nest-loop joins
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/executor/nodeNestloop.c,v 1.52 2009/04/02 20:59:10 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 *	 INTERFACE ROUTINES
 *		ExecNestLoop	 - process a nestloop join of two plans
 *		ExecInitNestLoop - initialize the join
 *		ExecEndNestLoop  - shut down the join
 */

#include "postgres.h"

#include "executor/execdebug.h"
#include "executor/nodeNestloop.h"
#include "utils/memutils.h"


/* ----------------------------------------------------------------
 *		ExecNestLoop(node)
 *
 * old comments
 *		Returns the tuple joined from inner and outer tuples which
 *		satisfies the qualification clause.
 *
 *		It scans the inner relation to join with current outer tuple.
 *
 *		If none is found, next tuple from the outer relation is retrieved
 *		and the inner relation is scanned from the beginning again to join
 *		with the outer tuple.
 *
 *		NULL is returned if all the remaining outer tuples are tried and
 *		all fail to join with the inner tuples.
 *
 *		NULL is also returned if there is no tuple from inner relation.
 *
 *		Conditions:
 *		  -- outerTuple contains current tuple from outer relation and
 *			 the right son(inner relation) maintains "cursor" at the tuple
 *			 returned previously.
 *				This is achieved by maintaining a scan position on the outer
 *				relation.
 *
 *		Initial States:
 *		  -- the outer child and the inner child
 *			   are prepared to return the first tuple.
 * ----------------------------------------------------------------
 */
TupleTableSlot *
ExecNestLoop(NestLoopState *node)
{
	PlanState  *innerPlan;
	PlanState  *outerPlan;
	TupleTableSlot *outerTupleSlot;
	TupleTableSlot *innerTupleSlot;
	List	   *joinqual;
	List	   *otherqual;
	ExprContext *econtext;

	/*
	 * get information from the node
	 */
	ENL1_printf("getting info from node");

	joinqual = node->js.joinqual;
	otherqual = node->js.ps.qual;
	outerPlan = outerPlanState(node);
	innerPlan = innerPlanState(node);
	econtext = node->js.ps.ps_ExprContext;

	/*
	 * Check to see if we're still projecting out tuples from a previous join
	 * tuple (because there is a function-returning-set in the projection
	 * expressions).  If so, try to project another one.
	 */
	if (node->js.ps.ps_TupFromTlist)
	{
		TupleTableSlot *result;
		ExprDoneCond isDone;

		result = ExecProject(node->js.ps.ps_ProjInfo, &isDone);
		if (isDone == ExprMultipleResult)
			return result;
		/* Done with that source tuple... */
		node->js.ps.ps_TupFromTlist = false;
	}

	/*
	 * Reset per-tuple memory context to free any expression evaluation
	 * storage allocated in the previous tuple cycle.  Note this can't happen
	 * until we're done projecting out tuples from a join tuple.
	 */
	ResetExprContext(econtext);

	/*
	 * Ok, everything is setup for the join so now loop until we return a
	 * qualifying join tuple.
	 */
	ENL1_printf("entering main loop");

	for (;;)
	{
		/*
		 * If we don't have an outer tuple, get the next one and reset the
		 * inner scan.
		 */
		if (node->nl_NeedNewOuter)
		{
			ENL1_printf("getting new outer tuple");
			outerTupleSlot = ExecProcNode(outerPlan);

			/*
			 * if there are no more outer tuples, then the join is complete..
			 */
			if (TupIsNull(outerTupleSlot))
			{
				ENL1_printf("no outer tuple, ending join");
				return NULL;
			}

			ENL1_printf("saving new outer tuple information");
			econtext->ecxt_outertuple = outerTupleSlot;
			node->nl_NeedNewOuter = false;
			node->nl_MatchedOuter = false;

			/*
			 * now rescan the inner plan
			 */
			ENL1_printf("rescanning inner plan");

			/*
			 * The scan key of the inner plan might depend on the current
			 * outer tuple (e.g. in index scans), that's why we pass our expr
			 * context.
			 */
			ExecReScan(innerPlan, econtext);
		}

		/*
		 * we have an outerTuple, try to get the next inner tuple.
		 */
		ENL1_printf("getting new inner tuple");

		innerTupleSlot = ExecProcNode(innerPlan);
		econtext->ecxt_innertuple = innerTupleSlot;

		if (TupIsNull(innerTupleSlot))
		{
			ENL1_printf("no inner tuple, need new outer tuple");

			node->nl_NeedNewOuter = true;

			if (!node->nl_MatchedOuter &&
				(node->js.jointype == JOIN_LEFT ||
				 node->js.jointype == JOIN_ANTI))
			{
				/*
				 * We are doing an outer join and there were no join matches
				 * for this outer tuple.  Generate a fake join tuple with
				 * nulls for the inner tuple, and return it if it passes the
				 * non-join quals.
				 */
				econtext->ecxt_innertuple = node->nl_NullInnerTupleSlot;

				ENL1_printf("testing qualification for outer-join tuple");

				if (otherqual == NIL || ExecQual(otherqual, econtext, false))
				{
					/*
					 * qualification was satisfied so we project and return
					 * the slot containing the result tuple using
					 * ExecProject().
					 */
					TupleTableSlot *result;
					ExprDoneCond isDone;

					ENL1_printf("qualification succeeded, projecting tuple");

					result = ExecProject(node->js.ps.ps_ProjInfo, &isDone);

					if (isDone != ExprEndResult)
					{
						node->js.ps.ps_TupFromTlist =
							(isDone == ExprMultipleResult);
						return result;
					}
				}
			}

			/*
			 * Otherwise just return to top of loop for a new outer tuple.
			 */
			continue;
		}

		/*
		 * at this point we have a new pair of inner and outer tuples so we
		 * test the inner and outer tuples to see if they satisfy the node's
		 * qualification.
		 *
		 * Only the joinquals determine MatchedOuter status, but all quals
		 * must pass to actually return the tuple.
		 */
		ENL1_printf("testing qualification");

		if (ExecQual(joinqual, econtext, false))
		{
			node->nl_MatchedOuter = true;

			/* In an antijoin, we never return a matched tuple */
			if (node->js.jointype == JOIN_ANTI)
			{
				node->nl_NeedNewOuter = true;
				continue;		/* return to top of loop */
			}

			/*
			 * In a semijoin, we'll consider returning the first match,
			 * but after that we're done with this outer tuple.
			 */
			if (node->js.jointype == JOIN_SEMI)
				node->nl_NeedNewOuter = true;

			if (otherqual == NIL || ExecQual(otherqual, econtext, false))
			{
				/*
				 * qualification was satisfied so we project and return the
				 * slot containing the result tuple using ExecProject().
				 */
				TupleTableSlot *result;
				ExprDoneCond isDone;

				ENL1_printf("qualification succeeded, projecting tuple");

				result = ExecProject(node->js.ps.ps_ProjInfo, &isDone);

				if (isDone != ExprEndResult)
				{
					node->js.ps.ps_TupFromTlist =
						(isDone == ExprMultipleResult);
					return result;
				}
			}
		}

		/*
		 * Tuple fails qual, so free per-tuple memory and try again.
		 */
		ResetExprContext(econtext);

		ENL1_printf("qualification failed, looping");
	}
}

/* ----------------------------------------------------------------
 *		ExecInitNestLoop
 * ----------------------------------------------------------------
 */
NestLoopState *
ExecInitNestLoop(NestLoop *node, EState *estate, int eflags)
{
	NestLoopState *nlstate;

	/* check for unsupported flags */
	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));

	NL1_printf("ExecInitNestLoop: %s\n",
			   "initializing node");

	/*
	 * create state structure
	 */
	nlstate = makeNode(NestLoopState);
	nlstate->js.ps.plan = (Plan *) node;
	nlstate->js.ps.state = estate;

	/*
	 * Miscellaneous initialization
	 *
	 * create expression context for node
	 */
	ExecAssignExprContext(estate, &nlstate->js.ps);

	/*
	 * initialize child expressions
	 */
	nlstate->js.ps.targetlist = (List *)
		ExecInitExpr((Expr *) node->join.plan.targetlist,
					 (PlanState *) nlstate);
	nlstate->js.ps.qual = (List *)
		ExecInitExpr((Expr *) node->join.plan.qual,
					 (PlanState *) nlstate);
	nlstate->js.jointype = node->join.jointype;
	nlstate->js.joinqual = (List *)
		ExecInitExpr((Expr *) node->join.joinqual,
					 (PlanState *) nlstate);

	/*
	 * initialize child nodes
	 *
	 * Tell the inner child that cheap rescans would be good.  (This is
	 * unnecessary if we are doing nestloop with inner indexscan, because the
	 * rescan will always be with a fresh parameter --- but since
	 * nodeIndexscan doesn't actually care about REWIND, there's no point in
	 * dealing with that refinement.)
	 */
	outerPlanState(nlstate) = ExecInitNode(outerPlan(node), estate, eflags);
	innerPlanState(nlstate) = ExecInitNode(innerPlan(node), estate,
										   eflags | EXEC_FLAG_REWIND);

#define NESTLOOP_NSLOTS 2

	/*
	 * tuple table initialization
	 */
	ExecInitResultTupleSlot(estate, &nlstate->js.ps);

	switch (node->join.jointype)
	{
		case JOIN_INNER:
		case JOIN_SEMI:
			break;
		case JOIN_LEFT:
		case JOIN_ANTI:
			nlstate->nl_NullInnerTupleSlot =
				ExecInitNullTupleSlot(estate,
								 ExecGetResultType(innerPlanState(nlstate)));
			break;
		default:
			elog(ERROR, "unrecognized join type: %d",
				 (int) node->join.jointype);
	}

	/*
	 * initialize tuple type and projection info
	 */
	ExecAssignResultTypeFromTL(&nlstate->js.ps);
	ExecAssignProjectionInfo(&nlstate->js.ps, NULL);

	/*
	 * finally, wipe the current outer tuple clean.
	 */
	nlstate->js.ps.ps_TupFromTlist = false;
	nlstate->nl_NeedNewOuter = true;
	nlstate->nl_MatchedOuter = false;

	NL1_printf("ExecInitNestLoop: %s\n",
			   "node initialized");

	return nlstate;
}

int
ExecCountSlotsNestLoop(NestLoop *node)
{
	return ExecCountSlotsNode(outerPlan(node)) +
		ExecCountSlotsNode(innerPlan(node)) +
		NESTLOOP_NSLOTS;
}

/* ----------------------------------------------------------------
 *		ExecEndNestLoop
 *
 *		closes down scans and frees allocated storage
 * ----------------------------------------------------------------
 */
void
ExecEndNestLoop(NestLoopState *node)
{
	NL1_printf("ExecEndNestLoop: %s\n",
			   "ending node processing");

	/*
	 * Free the exprcontext
	 */
	ExecFreeExprContext(&node->js.ps);

	/*
	 * clean out the tuple table
	 */
	ExecClearTuple(node->js.ps.ps_ResultTupleSlot);

	/*
	 * close down subplans
	 */
	ExecEndNode(outerPlanState(node));
	ExecEndNode(innerPlanState(node));

	NL1_printf("ExecEndNestLoop: %s\n",
			   "node processing ended");
}

/* ----------------------------------------------------------------
 *		ExecReScanNestLoop
 * ----------------------------------------------------------------
 */
void
ExecReScanNestLoop(NestLoopState *node, ExprContext *exprCtxt)
{
	PlanState  *outerPlan = outerPlanState(node);

	/*
	 * If outerPlan->chgParam is not null then plan will be automatically
	 * re-scanned by first ExecProcNode. innerPlan is re-scanned for each new
	 * outer tuple and MUST NOT be re-scanned from here or you'll get troubles
	 * from inner index scans when outer Vars are used as run-time keys...
	 */
	if (outerPlan->chgParam == NULL)
		ExecReScan(outerPlan, exprCtxt);

	node->js.ps.ps_TupFromTlist = false;
	node->nl_NeedNewOuter = true;
	node->nl_MatchedOuter = false;
}