postgresql/src/backend/executor/nodeHashjoin.c

/*-------------------------------------------------------------------------
 *
 * nodeHashjoin.c
 *	  Routines to handle hash join nodes
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/executor/nodeHashjoin.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "executor/executor.h"
#include "executor/hashjoin.h"
#include "executor/nodeHash.h"
#include "executor/nodeHashjoin.h"
#include "miscadmin.h"
#include "utils/memutils.h"


/*
 * States of the ExecHashJoin state machine
 */
#define HJ_BUILD_HASHTABLE		1
#define HJ_NEED_NEW_OUTER		2
#define HJ_SCAN_BUCKET			3
#define HJ_FILL_OUTER_TUPLE		4
#define HJ_FILL_INNER_TUPLES	5
#define HJ_NEED_NEW_BATCH		6

/* Returns true if doing null-fill on outer relation */
#define HJ_FILL_OUTER(hjstate)	((hjstate)->hj_NullInnerTupleSlot != NULL)
/* Returns true if doing null-fill on inner relation */
#define HJ_FILL_INNER(hjstate)	((hjstate)->hj_NullOuterTupleSlot != NULL)

static TupleTableSlot *ExecHashJoinOuterGetTuple(PlanState *outerNode,
						  HashJoinState *hjstate,
						  uint32 *hashvalue);
static TupleTableSlot *ExecHashJoinGetSavedTuple(HashJoinState *hjstate,
						  BufFile *file,
						  uint32 *hashvalue,
						  TupleTableSlot *tupleSlot);
static bool ExecHashJoinNewBatch(HashJoinState *hjstate);


/* ----------------------------------------------------------------
 *		ExecHashJoin
 *
 *		This function implements the Hybrid Hashjoin algorithm.
 *
 *		Note: the relation we build hash table on is the "inner"
 *			  the other one is "outer".
 * ----------------------------------------------------------------
 */
static TupleTableSlot *			/* return: a tuple or NULL */
ExecHashJoin(PlanState *pstate)
{
	HashJoinState *node = castNode(HashJoinState, pstate);
	PlanState  *outerNode;
	HashState  *hashNode;
	ExprState  *joinqual;
	ExprState  *otherqual;
	ExprContext *econtext;
	HashJoinTable hashtable;
	TupleTableSlot *outerTupleSlot;
	uint32		hashvalue;
	int			batchno;

	/*
	 * get information from HashJoin node
	 */
	joinqual = node->js.joinqual;
	otherqual = node->js.ps.qual;
	hashNode = (HashState *) innerPlanState(node);
	outerNode = outerPlanState(node);
	hashtable = node->hj_HashTable;
	econtext = node->js.ps.ps_ExprContext;

	/*
	 * Reset per-tuple memory context to free any expression evaluation
	 * storage allocated in the previous tuple cycle.
	 */
	ResetExprContext(econtext);

	/*
	 * run the hash join state machine
	 */
	for (;;)
	{
		/*
		 * It's possible to iterate this loop many times before returning a
		 * tuple, in some pathological cases such as needing to move much of
		 * the current batch to a later batch.  So let's check for interrupts
		 * each time through.
		 */
		CHECK_FOR_INTERRUPTS();

		switch (node->hj_JoinState)
		{
			case HJ_BUILD_HASHTABLE:

				/*
				 * First time through: build hash table for inner relation.
				 */
				Assert(hashtable == NULL);

				/*
				 * If the outer relation is completely empty, and it's not
				 * right/full join, we can quit without building the hash
				 * table.  However, for an inner join it is only a win to
				 * check this when the outer relation's startup cost is less
				 * than the projected cost of building the hash table.
				 * Otherwise it's best to build the hash table first and see
				 * if the inner relation is empty.  (When it's a left join, we
				 * should always make this check, since we aren't going to be
				 * able to skip the join on the strength of an empty inner
				 * relation anyway.)
				 *
				 * If we are rescanning the join, we make use of information
				 * gained on the previous scan: don't bother to try the
				 * prefetch if the previous scan found the outer relation
				 * nonempty. This is not 100% reliable since with new
				 * parameters the outer relation might yield different
				 * results, but it's a good heuristic.
				 *
				 * The only way to make the check is to try to fetch a tuple
				 * from the outer plan node.  If we succeed, we have to stash
				 * it away for later consumption by ExecHashJoinOuterGetTuple.
				 */
				if (HJ_FILL_INNER(node))
				{
					/* no chance to not build the hash table */
					node->hj_FirstOuterTupleSlot = NULL;
				}
				else if (HJ_FILL_OUTER(node) ||
						 (outerNode->plan->startup_cost < hashNode->ps.plan->total_cost &&
						  !node->hj_OuterNotEmpty))
				{
					node->hj_FirstOuterTupleSlot = ExecProcNode(outerNode);
					if (TupIsNull(node->hj_FirstOuterTupleSlot))
					{
						node->hj_OuterNotEmpty = false;
						return NULL;
					}
					else
						node->hj_OuterNotEmpty = true;
				}
				else
					node->hj_FirstOuterTupleSlot = NULL;

				/*
				 * create the hash table
				 */
				hashtable = ExecHashTableCreate((Hash *) hashNode->ps.plan,
												node->hj_HashOperators,
												HJ_FILL_INNER(node));
				node->hj_HashTable = hashtable;

				/*
				 * execute the Hash node, to build the hash table
				 */
				hashNode->hashtable = hashtable;
				(void) MultiExecProcNode((PlanState *) hashNode);

				/*
				 * If the inner relation is completely empty, and we're not
				 * doing a left outer join, we can quit without scanning the
				 * outer relation.
				 */
				if (hashtable->totalTuples == 0 && !HJ_FILL_OUTER(node))
					return NULL;

				/*
				 * need to remember whether nbatch has increased since we
				 * began scanning the outer relation
				 */
				hashtable->nbatch_outstart = hashtable->nbatch;

				/*
				 * Reset OuterNotEmpty for scan.  (It's OK if we fetched a
				 * tuple above, because ExecHashJoinOuterGetTuple will
				 * immediately set it again.)
				 */
				node->hj_OuterNotEmpty = false;

				node->hj_JoinState = HJ_NEED_NEW_OUTER;

				/* FALL THRU */

			case HJ_NEED_NEW_OUTER:

				/*
				 * We don't have an outer tuple, try to get the next one
				 */
				outerTupleSlot = ExecHashJoinOuterGetTuple(outerNode,
														   node,
														   &hashvalue);
				if (TupIsNull(outerTupleSlot))
				{
					/* end of batch, or maybe whole join */
					if (HJ_FILL_INNER(node))
					{
						/* set up to scan for unmatched inner tuples */
						ExecPrepHashTableForUnmatched(node);
						node->hj_JoinState = HJ_FILL_INNER_TUPLES;
					}
					else
						node->hj_JoinState = HJ_NEED_NEW_BATCH;
					continue;
				}

				econtext->ecxt_outertuple = outerTupleSlot;
				node->hj_MatchedOuter = false;

				/*
				 * Find the corresponding bucket for this tuple in the main
				 * hash table or skew hash table.
				 */
				node->hj_CurHashValue = hashvalue;
				ExecHashGetBucketAndBatch(hashtable, hashvalue,
										  &node->hj_CurBucketNo, &batchno);
				node->hj_CurSkewBucketNo = ExecHashGetSkewBucket(hashtable,
																 hashvalue);
				node->hj_CurTuple = NULL;

				/*
				 * The tuple might not belong to the current batch (where
				 * "current batch" includes the skew buckets if any).
				 */
				if (batchno != hashtable->curbatch &&
					node->hj_CurSkewBucketNo == INVALID_SKEW_BUCKET_NO)
				{
					/*
					 * Need to postpone this outer tuple to a later batch.
					 * Save it in the corresponding outer-batch file.
					 */
					Assert(batchno > hashtable->curbatch);
					ExecHashJoinSaveTuple(ExecFetchSlotMinimalTuple(outerTupleSlot),
										  hashvalue,
										  &hashtable->outerBatchFile[batchno]);
					/* Loop around, staying in HJ_NEED_NEW_OUTER state */
					continue;
				}

				/* OK, let's scan the bucket for matches */
				node->hj_JoinState = HJ_SCAN_BUCKET;

				/* FALL THRU */

			case HJ_SCAN_BUCKET:

				/*
				 * Scan the selected hash bucket for matches to current outer
				 */
				if (!ExecScanHashBucket(node, econtext))
				{
					/* out of matches; check for possible outer-join fill */
					node->hj_JoinState = HJ_FILL_OUTER_TUPLE;
					continue;
				}

				/*
				 * We've got a match, but still need to test non-hashed quals.
				 * ExecScanHashBucket already set up all the state needed to
				 * call ExecQual.
				 *
				 * If we pass the qual, then save state for next call and have
				 * ExecProject form the projection, store it in the tuple
				 * table, and return the slot.
				 *
				 * Only the joinquals determine tuple match status, but all
				 * quals must pass to actually return the tuple.
				 */
				if (joinqual == NULL || ExecQual(joinqual, econtext))
				{
					node->hj_MatchedOuter = true;
					HeapTupleHeaderSetMatch(HJTUPLE_MINTUPLE(node->hj_CurTuple));

					/* In an antijoin, we never return a matched tuple */
					if (node->js.jointype == JOIN_ANTI)
					{
						node->hj_JoinState = HJ_NEED_NEW_OUTER;
						continue;
					}

					/*
					 * If we only need to join to the first matching inner
					 * tuple, then consider returning this one, but after that
					 * continue with next outer tuple.
					 */
					if (node->js.single_match)
						node->hj_JoinState = HJ_NEED_NEW_OUTER;

					if (otherqual == NULL || ExecQual(otherqual, econtext))
						return ExecProject(node->js.ps.ps_ProjInfo);
					else
						InstrCountFiltered2(node, 1);
				}
				else
					InstrCountFiltered1(node, 1);
				break;

			case HJ_FILL_OUTER_TUPLE:

				/*
				 * The current outer tuple has run out of matches, so check
				 * whether to emit a dummy outer-join tuple.  Whether we emit
				 * one or not, the next state is NEED_NEW_OUTER.
				 */
				node->hj_JoinState = HJ_NEED_NEW_OUTER;

				if (!node->hj_MatchedOuter &&
					HJ_FILL_OUTER(node))
				{
					/*
					 * 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->hj_NullInnerTupleSlot;

					if (otherqual == NULL || ExecQual(otherqual, econtext))
						return ExecProject(node->js.ps.ps_ProjInfo);
					else
						InstrCountFiltered2(node, 1);
				}
				break;

			case HJ_FILL_INNER_TUPLES:

				/*
				 * We have finished a batch, but we are doing right/full join,
				 * so any unmatched inner tuples in the hashtable have to be
				 * emitted before we continue to the next batch.
				 */
				if (!ExecScanHashTableForUnmatched(node, econtext))
				{
					/* no more unmatched tuples */
					node->hj_JoinState = HJ_NEED_NEW_BATCH;
					continue;
				}

				/*
				 * Generate a fake join tuple with nulls for the outer tuple,
				 * and return it if it passes the non-join quals.
				 */
				econtext->ecxt_outertuple = node->hj_NullOuterTupleSlot;

				if (otherqual == NULL || ExecQual(otherqual, econtext))
					return ExecProject(node->js.ps.ps_ProjInfo);
				else
					InstrCountFiltered2(node, 1);
				break;

			case HJ_NEED_NEW_BATCH:

				/*
				 * Try to advance to next batch.  Done if there are no more.
				 */
				if (!ExecHashJoinNewBatch(node))
					return NULL;	/* end of join */
				node->hj_JoinState = HJ_NEED_NEW_OUTER;
				break;

			default:
				elog(ERROR, "unrecognized hashjoin state: %d",
					 (int) node->hj_JoinState);
		}
	}
}

/* ----------------------------------------------------------------
 *		ExecInitHashJoin
 *
 *		Init routine for HashJoin node.
 * ----------------------------------------------------------------
 */
HashJoinState *
ExecInitHashJoin(HashJoin *node, EState *estate, int eflags)
{
	HashJoinState *hjstate;
	Plan	   *outerNode;
	Hash	   *hashNode;
	List	   *lclauses;
	List	   *rclauses;
	List	   *hoperators;
	ListCell   *l;

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

	/*
	 * create state structure
	 */
	hjstate = makeNode(HashJoinState);
	hjstate->js.ps.plan = (Plan *) node;
	hjstate->js.ps.state = estate;
	hjstate->js.ps.ExecProcNode = ExecHashJoin;

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

	/*
	 * initialize child expressions
	 */
	hjstate->js.ps.qual =
		ExecInitQual(node->join.plan.qual, (PlanState *) hjstate);
	hjstate->js.jointype = node->join.jointype;
	hjstate->js.joinqual =
		ExecInitQual(node->join.joinqual, (PlanState *) hjstate);
	hjstate->hashclauses =
		ExecInitQual(node->hashclauses, (PlanState *) hjstate);

	/*
	 * initialize child nodes
	 *
	 * Note: we could suppress the REWIND flag for the inner input, which
	 * would amount to betting that the hash will be a single batch.  Not
	 * clear if this would be a win or not.
	 */
	outerNode = outerPlan(node);
	hashNode = (Hash *) innerPlan(node);

	outerPlanState(hjstate) = ExecInitNode(outerNode, estate, eflags);
	innerPlanState(hjstate) = ExecInitNode((Plan *) hashNode, estate, eflags);

	/*
	 * tuple table initialization
	 */
	ExecInitResultTupleSlot(estate, &hjstate->js.ps);
	hjstate->hj_OuterTupleSlot = ExecInitExtraTupleSlot(estate);

	/*
	 * detect whether we need only consider the first matching inner tuple
	 */
	hjstate->js.single_match = (node->join.inner_unique ||
								node->join.jointype == JOIN_SEMI);

	/* set up null tuples for outer joins, if needed */
	switch (node->join.jointype)
	{
		case JOIN_INNER:
		case JOIN_SEMI:
			break;
		case JOIN_LEFT:
		case JOIN_ANTI:
			hjstate->hj_NullInnerTupleSlot =
				ExecInitNullTupleSlot(estate,
									  ExecGetResultType(innerPlanState(hjstate)));
			break;
		case JOIN_RIGHT:
			hjstate->hj_NullOuterTupleSlot =
				ExecInitNullTupleSlot(estate,
									  ExecGetResultType(outerPlanState(hjstate)));
			break;
		case JOIN_FULL:
			hjstate->hj_NullOuterTupleSlot =
				ExecInitNullTupleSlot(estate,
									  ExecGetResultType(outerPlanState(hjstate)));
			hjstate->hj_NullInnerTupleSlot =
				ExecInitNullTupleSlot(estate,
									  ExecGetResultType(innerPlanState(hjstate)));
			break;
		default:
			elog(ERROR, "unrecognized join type: %d",
				 (int) node->join.jointype);
	}

	/*
	 * now for some voodoo.  our temporary tuple slot is actually the result
	 * tuple slot of the Hash node (which is our inner plan).  we can do this
	 * because Hash nodes don't return tuples via ExecProcNode() -- instead
	 * the hash join node uses ExecScanHashBucket() to get at the contents of
	 * the hash table.  -cim 6/9/91
	 */
	{
		HashState  *hashstate = (HashState *) innerPlanState(hjstate);
		TupleTableSlot *slot = hashstate->ps.ps_ResultTupleSlot;

		hjstate->hj_HashTupleSlot = slot;
	}

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

	ExecSetSlotDescriptor(hjstate->hj_OuterTupleSlot,
						  ExecGetResultType(outerPlanState(hjstate)));

	/*
	 * initialize hash-specific info
	 */
	hjstate->hj_HashTable = NULL;
	hjstate->hj_FirstOuterTupleSlot = NULL;

	hjstate->hj_CurHashValue = 0;
	hjstate->hj_CurBucketNo = 0;
	hjstate->hj_CurSkewBucketNo = INVALID_SKEW_BUCKET_NO;
	hjstate->hj_CurTuple = NULL;

	/*
	 * Deconstruct the hash clauses into outer and inner argument values, so
	 * that we can evaluate those subexpressions separately.  Also make a list
	 * of the hash operator OIDs, in preparation for looking up the hash
	 * functions to use.
	 */
	lclauses = NIL;
	rclauses = NIL;
	hoperators = NIL;
	foreach(l, node->hashclauses)
	{
		OpExpr	   *hclause = lfirst_node(OpExpr, l);

		lclauses = lappend(lclauses, ExecInitExpr(linitial(hclause->args),
												  (PlanState *) hjstate));
		rclauses = lappend(rclauses, ExecInitExpr(lsecond(hclause->args),
												  (PlanState *) hjstate));
		hoperators = lappend_oid(hoperators, hclause->opno);
	}
	hjstate->hj_OuterHashKeys = lclauses;
	hjstate->hj_InnerHashKeys = rclauses;
	hjstate->hj_HashOperators = hoperators;
	/* child Hash node needs to evaluate inner hash keys, too */
	((HashState *) innerPlanState(hjstate))->hashkeys = rclauses;

	hjstate->hj_JoinState = HJ_BUILD_HASHTABLE;
	hjstate->hj_MatchedOuter = false;
	hjstate->hj_OuterNotEmpty = false;

	return hjstate;
}

/* ----------------------------------------------------------------
 *		ExecEndHashJoin
 *
 *		clean up routine for HashJoin node
 * ----------------------------------------------------------------
 */
void
ExecEndHashJoin(HashJoinState *node)
{
	/*
	 * Free hash table
	 */
	if (node->hj_HashTable)
	{
		ExecHashTableDestroy(node->hj_HashTable);
		node->hj_HashTable = NULL;
	}

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

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

	/*
	 * clean up subtrees
	 */
	ExecEndNode(outerPlanState(node));
	ExecEndNode(innerPlanState(node));
}

/*
 * ExecHashJoinOuterGetTuple
 *
 *		get the next outer tuple for hashjoin: either by
 *		executing the outer plan node in the first pass, or from
 *		the temp files for the hashjoin batches.
 *
 * Returns a null slot if no more outer tuples (within the current batch).
 *
 * On success, the tuple's hash value is stored at *hashvalue --- this is
 * either originally computed, or re-read from the temp file.
 */
static TupleTableSlot *
ExecHashJoinOuterGetTuple(PlanState *outerNode,
						  HashJoinState *hjstate,
						  uint32 *hashvalue)
{
	HashJoinTable hashtable = hjstate->hj_HashTable;
	int			curbatch = hashtable->curbatch;
	TupleTableSlot *slot;

	if (curbatch == 0)			/* if it is the first pass */
	{
		/*
		 * Check to see if first outer tuple was already fetched by
		 * ExecHashJoin() and not used yet.
		 */
		slot = hjstate->hj_FirstOuterTupleSlot;
		if (!TupIsNull(slot))
			hjstate->hj_FirstOuterTupleSlot = NULL;
		else
			slot = ExecProcNode(outerNode);

		while (!TupIsNull(slot))
		{
			/*
			 * We have to compute the tuple's hash value.
			 */
			ExprContext *econtext = hjstate->js.ps.ps_ExprContext;

			econtext->ecxt_outertuple = slot;
			if (ExecHashGetHashValue(hashtable, econtext,
									 hjstate->hj_OuterHashKeys,
									 true,	/* outer tuple */
									 HJ_FILL_OUTER(hjstate),
									 hashvalue))
			{
				/* remember outer relation is not empty for possible rescan */
				hjstate->hj_OuterNotEmpty = true;

				return slot;
			}

			/*
			 * That tuple couldn't match because of a NULL, so discard it and
			 * continue with the next one.
			 */
			slot = ExecProcNode(outerNode);
		}
	}
	else if (curbatch < hashtable->nbatch)
	{
		BufFile    *file = hashtable->outerBatchFile[curbatch];

		/*
		 * In outer-join cases, we could get here even though the batch file
		 * is empty.
		 */
		if (file == NULL)
			return NULL;

		slot = ExecHashJoinGetSavedTuple(hjstate,
										 file,
										 hashvalue,
										 hjstate->hj_OuterTupleSlot);
		if (!TupIsNull(slot))
			return slot;
	}

	/* End of this batch */
	return NULL;
}

/*
 * ExecHashJoinNewBatch
 *		switch to a new hashjoin batch
 *
 * Returns true if successful, false if there are no more batches.
 */
static bool
ExecHashJoinNewBatch(HashJoinState *hjstate)
{
	HashJoinTable hashtable = hjstate->hj_HashTable;
	int			nbatch;
	int			curbatch;
	BufFile    *innerFile;
	TupleTableSlot *slot;
	uint32		hashvalue;

	nbatch = hashtable->nbatch;
	curbatch = hashtable->curbatch;

	if (curbatch > 0)
	{
		/*
		 * We no longer need the previous outer batch file; close it right
		 * away to free disk space.
		 */
		if (hashtable->outerBatchFile[curbatch])
			BufFileClose(hashtable->outerBatchFile[curbatch]);
		hashtable->outerBatchFile[curbatch] = NULL;
	}
	else						/* we just finished the first batch */
	{
		/*
		 * Reset some of the skew optimization state variables, since we no
		 * longer need to consider skew tuples after the first batch. The
		 * memory context reset we are about to do will release the skew
		 * hashtable itself.
		 */
		hashtable->skewEnabled = false;
		hashtable->skewBucket = NULL;
		hashtable->skewBucketNums = NULL;
		hashtable->nSkewBuckets = 0;
		hashtable->spaceUsedSkew = 0;
	}

	/*
	 * We can always skip over any batches that are completely empty on both
	 * sides.  We can sometimes skip over batches that are empty on only one
	 * side, but there are exceptions:
	 *
	 * 1. In a left/full outer join, we have to process outer batches even if
	 * the inner batch is empty.  Similarly, in a right/full outer join, we
	 * have to process inner batches even if the outer batch is empty.
	 *
	 * 2. If we have increased nbatch since the initial estimate, we have to
	 * scan inner batches since they might contain tuples that need to be
	 * reassigned to later inner batches.
	 *
	 * 3. Similarly, if we have increased nbatch since starting the outer
	 * scan, we have to rescan outer batches in case they contain tuples that
	 * need to be reassigned.
	 */
	curbatch++;
	while (curbatch < nbatch &&
		   (hashtable->outerBatchFile[curbatch] == NULL ||
			hashtable->innerBatchFile[curbatch] == NULL))
	{
		if (hashtable->outerBatchFile[curbatch] &&
			HJ_FILL_OUTER(hjstate))
			break;				/* must process due to rule 1 */
		if (hashtable->innerBatchFile[curbatch] &&
			HJ_FILL_INNER(hjstate))
			break;				/* must process due to rule 1 */
		if (hashtable->innerBatchFile[curbatch] &&
			nbatch != hashtable->nbatch_original)
			break;				/* must process due to rule 2 */
		if (hashtable->outerBatchFile[curbatch] &&
			nbatch != hashtable->nbatch_outstart)
			break;				/* must process due to rule 3 */
		/* We can ignore this batch. */
		/* Release associated temp files right away. */
		if (hashtable->innerBatchFile[curbatch])
			BufFileClose(hashtable->innerBatchFile[curbatch]);
		hashtable->innerBatchFile[curbatch] = NULL;
		if (hashtable->outerBatchFile[curbatch])
			BufFileClose(hashtable->outerBatchFile[curbatch]);
		hashtable->outerBatchFile[curbatch] = NULL;
		curbatch++;
	}

	if (curbatch >= nbatch)
		return false;			/* no more batches */

	hashtable->curbatch = curbatch;

	/*
	 * Reload the hash table with the new inner batch (which could be empty)
	 */
	ExecHashTableReset(hashtable);

	innerFile = hashtable->innerBatchFile[curbatch];

	if (innerFile != NULL)
	{
		if (BufFileSeek(innerFile, 0, 0L, SEEK_SET))
			ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("could not rewind hash-join temporary file: %m")));

		while ((slot = ExecHashJoinGetSavedTuple(hjstate,
												 innerFile,
												 &hashvalue,
												 hjstate->hj_HashTupleSlot)))
		{
			/*
			 * NOTE: some tuples may be sent to future batches.  Also, it is
			 * possible for hashtable->nbatch to be increased here!
			 */
			ExecHashTableInsert(hashtable, slot, hashvalue);
		}

		/*
		 * after we build the hash table, the inner batch file is no longer
		 * needed
		 */
		BufFileClose(innerFile);
		hashtable->innerBatchFile[curbatch] = NULL;
	}

	/*
	 * Rewind outer batch file (if present), so that we can start reading it.
	 */
	if (hashtable->outerBatchFile[curbatch] != NULL)
	{
		if (BufFileSeek(hashtable->outerBatchFile[curbatch], 0, 0L, SEEK_SET))
			ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("could not rewind hash-join temporary file: %m")));
	}

	return true;
}

/*
 * ExecHashJoinSaveTuple
 *		save a tuple to a batch file.
 *
 * The data recorded in the file for each tuple is its hash value,
 * then the tuple in MinimalTuple format.
 *
 * Note: it is important always to call this in the regular executor
 * context, not in a shorter-lived context; else the temp file buffers
 * will get messed up.
 */
void
ExecHashJoinSaveTuple(MinimalTuple tuple, uint32 hashvalue,
					  BufFile **fileptr)
{
	BufFile    *file = *fileptr;
	size_t		written;

	if (file == NULL)
	{
		/* First write to this batch file, so open it. */
		file = BufFileCreateTemp(false);
		*fileptr = file;
	}

	written = BufFileWrite(file, (void *) &hashvalue, sizeof(uint32));
	if (written != sizeof(uint32))
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not write to hash-join temporary file: %m")));

	written = BufFileWrite(file, (void *) tuple, tuple->t_len);
	if (written != tuple->t_len)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not write to hash-join temporary file: %m")));
}

/*
 * ExecHashJoinGetSavedTuple
 *		read the next tuple from a batch file.  Return NULL if no more.
 *
 * On success, *hashvalue is set to the tuple's hash value, and the tuple
 * itself is stored in the given slot.
 */
static TupleTableSlot *
ExecHashJoinGetSavedTuple(HashJoinState *hjstate,
						  BufFile *file,
						  uint32 *hashvalue,
						  TupleTableSlot *tupleSlot)
{
	uint32		header[2];
	size_t		nread;
	MinimalTuple tuple;

	/*
	 * We check for interrupts here because this is typically taken as an
	 * alternative code path to an ExecProcNode() call, which would include
	 * such a check.
	 */
	CHECK_FOR_INTERRUPTS();

	/*
	 * Since both the hash value and the MinimalTuple length word are uint32,
	 * we can read them both in one BufFileRead() call without any type
	 * cheating.
	 */
	nread = BufFileRead(file, (void *) header, sizeof(header));
	if (nread == 0)				/* end of file */
	{
		ExecClearTuple(tupleSlot);
		return NULL;
	}
	if (nread != sizeof(header))
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not read from hash-join temporary file: %m")));
	*hashvalue = header[0];
	tuple = (MinimalTuple) palloc(header[1]);
	tuple->t_len = header[1];
	nread = BufFileRead(file,
						(void *) ((char *) tuple + sizeof(uint32)),
						header[1] - sizeof(uint32));
	if (nread != header[1] - sizeof(uint32))
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not read from hash-join temporary file: %m")));
	return ExecStoreMinimalTuple(tuple, tupleSlot, true);
}


void
ExecReScanHashJoin(HashJoinState *node)
{
	/*
	 * In a multi-batch join, we currently have to do rescans the hard way,
	 * primarily because batch temp files may have already been released. But
	 * if it's a single-batch join, and there is no parameter change for the
	 * inner subnode, then we can just re-use the existing hash table without
	 * rebuilding it.
	 */
	if (node->hj_HashTable != NULL)
	{
		if (node->hj_HashTable->nbatch == 1 &&
			node->js.ps.righttree->chgParam == NULL)
		{
			/*
			 * Okay to reuse the hash table; needn't rescan inner, either.
			 *
			 * However, if it's a right/full join, we'd better reset the
			 * inner-tuple match flags contained in the table.
			 */
			if (HJ_FILL_INNER(node))
				ExecHashTableResetMatchFlags(node->hj_HashTable);

			/*
			 * Also, we need to reset our state about the emptiness of the
			 * outer relation, so that the new scan of the outer will update
			 * it correctly if it turns out to be empty this time. (There's no
			 * harm in clearing it now because ExecHashJoin won't need the
			 * info.  In the other cases, where the hash table doesn't exist
			 * or we are destroying it, we leave this state alone because
			 * ExecHashJoin will need it the first time through.)
			 */
			node->hj_OuterNotEmpty = false;

			/* ExecHashJoin can skip the BUILD_HASHTABLE step */
			node->hj_JoinState = HJ_NEED_NEW_OUTER;
		}
		else
		{
			/* must destroy and rebuild hash table */
			ExecHashTableDestroy(node->hj_HashTable);
			node->hj_HashTable = NULL;
			node->hj_JoinState = HJ_BUILD_HASHTABLE;

			/*
			 * if chgParam of subnode is not null then plan will be re-scanned
			 * by first ExecProcNode.
			 */
			if (node->js.ps.righttree->chgParam == NULL)
				ExecReScan(node->js.ps.righttree);
		}
	}

	/* Always reset intra-tuple state */
	node->hj_CurHashValue = 0;
	node->hj_CurBucketNo = 0;
	node->hj_CurSkewBucketNo = INVALID_SKEW_BUCKET_NO;
	node->hj_CurTuple = NULL;

	node->hj_MatchedOuter = false;
	node->hj_FirstOuterTupleSlot = NULL;

	/*
	 * if chgParam of subnode is not null then plan will be re-scanned by
	 * first ExecProcNode.
	 */
	if (node->js.ps.lefttree->chgParam == NULL)
		ExecReScan(node->js.ps.lefttree);
}