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Tom Lane authored
selecting power-of-2, rather than prime, numbers of buckets in hash joins. If the hash functions are doing their jobs properly by making all hash bits equally random, this is good enough, and it saves expensive integer division and modulus operations.
Tom Lane authoredselecting power-of-2, rather than prime, numbers of buckets in hash joins. If the hash functions are doing their jobs properly by making all hash bits equally random, this is good enough, and it saves expensive integer division and modulus operations.
nodeHash.c 22.97 KiB
/*-------------------------------------------------------------------------
*
* nodeHash.c
* Routines to hash relations for hashjoin
*
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeHash.c,v 1.112 2007/06/01 17:38:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/*
* INTERFACE ROUTINES
* MultiExecHash - generate an in-memory hash table of the relation
* ExecInitHash - initialize node and subnodes
* ExecEndHash - shutdown node and subnodes
*/
#include "postgres.h"
#include <math.h>
#include <limits.h>
#include "executor/execdebug.h"
#include "executor/hashjoin.h"
#include "executor/instrument.h"
#include "executor/nodeHash.h"
#include "executor/nodeHashjoin.h"
#include "miscadmin.h"
#include "parser/parse_expr.h"
#include "utils/dynahash.h"
#include "utils/memutils.h"
#include "utils/lsyscache.h"
static void ExecHashIncreaseNumBatches(HashJoinTable hashtable);
/* ----------------------------------------------------------------
* ExecHash
*
* stub for pro forma compliance
* ----------------------------------------------------------------
*/
TupleTableSlot *
ExecHash(HashState *node)
{
elog(ERROR, "Hash node does not support ExecProcNode call convention");
return NULL;
}
/* ----------------------------------------------------------------
* MultiExecHash
*
* build hash table for hashjoin, doing partitioning if more
* than one batch is required.
* ----------------------------------------------------------------
*/
Node *
MultiExecHash(HashState *node)
{
PlanState *outerNode;
List *hashkeys;
HashJoinTable hashtable;
TupleTableSlot *slot;
ExprContext *econtext;
uint32 hashvalue;
/* must provide our own instrumentation support */
if (node->ps.instrument)
InstrStartNode(node->ps.instrument);
/*
* get state info from node
*/
outerNode = outerPlanState(node);
hashtable = node->hashtable;
/*
* set expression context
*/
hashkeys = node->hashkeys;
econtext = node->ps.ps_ExprContext;
/*
* get all inner tuples and insert into the hash table (or temp files)
*/
for (;;)
{
slot = ExecProcNode(outerNode);
if (TupIsNull(slot))
break;
/* We have to compute the hash value */
econtext->ecxt_innertuple = slot;
if (ExecHashGetHashValue(hashtable, econtext, hashkeys, false, false,
&hashvalue))
{
ExecHashTableInsert(hashtable, slot, hashvalue);
hashtable->totalTuples += 1;
}
}
/* must provide our own instrumentation support */
if (node->ps.instrument)
InstrStopNode(node->ps.instrument, hashtable->totalTuples);
/*
* We do not return the hash table directly because it's not a subtype of
* Node, and so would violate the MultiExecProcNode API. Instead, our
* parent Hashjoin node is expected to know how to fish it out of our node
* state. Ugly but not really worth cleaning up, since Hashjoin knows
* quite a bit more about Hash besides that.
*/
return NULL;
}
/* ----------------------------------------------------------------
* ExecInitHash
*
* Init routine for Hash node
* ----------------------------------------------------------------
*/
HashState *
ExecInitHash(Hash *node, EState *estate, int eflags)
{
HashState *hashstate;
/* check for unsupported flags */
Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
/*
* create state structure
*/
hashstate = makeNode(HashState);
hashstate->ps.plan = (Plan *) node;
hashstate->ps.state = estate;
hashstate->hashtable = NULL; hashstate->hashkeys = NIL; /* will be set by parent HashJoin */
/*
* Miscellaneous initialization
*
* create expression context for node
*/
ExecAssignExprContext(estate, &hashstate->ps);
#define HASH_NSLOTS 1
/*
* initialize our result slot
*/
ExecInitResultTupleSlot(estate, &hashstate->ps);
/*
* initialize child expressions
*/
hashstate->ps.targetlist = (List *)
ExecInitExpr((Expr *) node->plan.targetlist,
(PlanState *) hashstate);
hashstate->ps.qual = (List *)
ExecInitExpr((Expr *) node->plan.qual,
(PlanState *) hashstate);
/*
* initialize child nodes
*/
outerPlanState(hashstate) = ExecInitNode(outerPlan(node), estate, eflags);
/*
* initialize tuple type. no need to initialize projection info because
* this node doesn't do projections
*/
ExecAssignResultTypeFromTL(&hashstate->ps);
hashstate->ps.ps_ProjInfo = NULL;
return hashstate;
}
int
ExecCountSlotsHash(Hash *node)
{
return ExecCountSlotsNode(outerPlan(node)) +
ExecCountSlotsNode(innerPlan(node)) +
HASH_NSLOTS;
}
/* ---------------------------------------------------------------
* ExecEndHash
*
* clean up routine for Hash node
* ----------------------------------------------------------------
*/
void
ExecEndHash(HashState *node)
{
PlanState *outerPlan;
/*
* free exprcontext
*/
ExecFreeExprContext(&node->ps);
/*
* shut down the subplan
*/
outerPlan = outerPlanState(node);
ExecEndNode(outerPlan);}
/* ----------------------------------------------------------------
* ExecHashTableCreate
*
* create an empty hashtable data structure for hashjoin.
* ----------------------------------------------------------------
*/
HashJoinTable
ExecHashTableCreate(Hash *node, List *hashOperators)
{
HashJoinTable hashtable;
Plan *outerNode;
int nbuckets;
int nbatch;
int log2_nbuckets;
int nkeys;
int i;
ListCell *ho;
MemoryContext oldcxt;
/*
* Get information about the size of the relation to be hashed (it's the
* "outer" subtree of this node, but the inner relation of the hashjoin).
* Compute the appropriate size of the hash table.
*/
outerNode = outerPlan(node);
ExecChooseHashTableSize(outerNode->plan_rows, outerNode->plan_width,
&nbuckets, &nbatch);
#ifdef HJDEBUG
printf("nbatch = %d, nbuckets = %d\n", nbatch, nbuckets);
#endif
/* nbuckets must be a power of 2 */
log2_nbuckets = my_log2(nbuckets);
Assert(nbuckets == (1 << log2_nbuckets));
/*
* Initialize the hash table control block.
*
* The hashtable control block is just palloc'd from the executor's
* per-query memory context.
*/
hashtable = (HashJoinTable) palloc(sizeof(HashJoinTableData));
hashtable->nbuckets = nbuckets;
hashtable->log2_nbuckets = log2_nbuckets;
hashtable->buckets = NULL;
hashtable->nbatch = nbatch;
hashtable->curbatch = 0;
hashtable->nbatch_original = nbatch;
hashtable->nbatch_outstart = nbatch;
hashtable->growEnabled = true;
hashtable->totalTuples = 0;
hashtable->innerBatchFile = NULL;
hashtable->outerBatchFile = NULL;
hashtable->spaceUsed = 0;
hashtable->spaceAllowed = work_mem * 1024L;
/*
* Get info about the hash functions to be used for each hash key.
* Also remember whether the join operators are strict.
*/
nkeys = list_length(hashOperators);
hashtable->outer_hashfunctions =
(FmgrInfo *) palloc(nkeys * sizeof(FmgrInfo));
hashtable->inner_hashfunctions =
(FmgrInfo *) palloc(nkeys * sizeof(FmgrInfo)); hashtable->hashStrict = (bool *) palloc(nkeys * sizeof(bool));
i = 0;
foreach(ho, hashOperators)
{
Oid hashop = lfirst_oid(ho);
Oid left_hashfn;
Oid right_hashfn;
if (!get_op_hash_functions(hashop, &left_hashfn, &right_hashfn))
elog(ERROR, "could not find hash function for hash operator %u",
hashop);
fmgr_info(left_hashfn, &hashtable->outer_hashfunctions[i]);
fmgr_info(right_hashfn, &hashtable->inner_hashfunctions[i]);
hashtable->hashStrict[i] = op_strict(hashop);
i++;
}
/*
* Create temporary memory contexts in which to keep the hashtable working
* storage. See notes in executor/hashjoin.h.
*/
hashtable->hashCxt = AllocSetContextCreate(CurrentMemoryContext,
"HashTableContext",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
hashtable->batchCxt = AllocSetContextCreate(hashtable->hashCxt,
"HashBatchContext",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
/* Allocate data that will live for the life of the hashjoin */
oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);
if (nbatch > 1)
{
/*
* allocate and initialize the file arrays in hashCxt
*/
hashtable->innerBatchFile = (BufFile **)
palloc0(nbatch * sizeof(BufFile *));
hashtable->outerBatchFile = (BufFile **)
palloc0(nbatch * sizeof(BufFile *));
/* The files will not be opened until needed... */
}
/*
* Prepare context for the first-scan space allocations; allocate the
* hashbucket array therein, and set each bucket "empty".
*/
MemoryContextSwitchTo(hashtable->batchCxt);
hashtable->buckets = (HashJoinTuple *)
palloc0(nbuckets * sizeof(HashJoinTuple));
MemoryContextSwitchTo(oldcxt);
return hashtable;
}
/*
* Compute appropriate size for hashtable given the estimated size of the
* relation to be hashed (number of rows and average row width).
*
* This is exported so that the planner's costsize.c can use it.
*/
/* Target bucket loading (tuples per bucket) */
#define NTUP_PER_BUCKET 10
void
ExecChooseHashTableSize(double ntuples, int tupwidth,
int *numbuckets,
int *numbatches)
{
int tupsize;
double inner_rel_bytes;
long hash_table_bytes;
int nbatch;
int nbuckets;
int i;
/* Force a plausible relation size if no info */
if (ntuples <= 0.0)
ntuples = 1000.0;
/*
* Estimate tupsize based on footprint of tuple in hashtable... note this
* does not allow for any palloc overhead. The manipulations of spaceUsed
* don't count palloc overhead either.
*/
tupsize = HJTUPLE_OVERHEAD +
MAXALIGN(sizeof(MinimalTupleData)) +
MAXALIGN(tupwidth);
inner_rel_bytes = ntuples * tupsize;
/*
* Target in-memory hashtable size is work_mem kilobytes.
*/
hash_table_bytes = work_mem * 1024L;
/*
* Set nbuckets to achieve an average bucket load of NTUP_PER_BUCKET when
* memory is filled. Set nbatch to the smallest power of 2 that appears
* sufficient.
*/
if (inner_rel_bytes > hash_table_bytes)
{
/* We'll need multiple batches */
long lbuckets;
double dbatch;
int minbatch;
lbuckets = (hash_table_bytes / tupsize) / NTUP_PER_BUCKET;
lbuckets = Min(lbuckets, INT_MAX / 2);
nbuckets = (int) lbuckets;
dbatch = ceil(inner_rel_bytes / hash_table_bytes);
dbatch = Min(dbatch, INT_MAX / 2);
minbatch = (int) dbatch;
nbatch = 2;
while (nbatch < minbatch)
nbatch <<= 1;
}
else
{
/* We expect the hashtable to fit in memory */
double dbuckets;
dbuckets = ceil(ntuples / NTUP_PER_BUCKET);
dbuckets = Min(dbuckets, INT_MAX / 2);
nbuckets = (int) dbuckets;
nbatch = 1;
}
/*
* Both nbuckets and nbatch must be powers of 2 to make
* ExecHashGetBucketAndBatch fast. We already fixed nbatch; now inflate
* nbuckets to the next larger power of 2. We also force nbuckets to not
* be real small, by starting the search at 2^10.
*/
i = 10;
while ((1 << i) < nbuckets)
i++;
nbuckets = (1 << i);
*numbuckets = nbuckets;
*numbatches = nbatch;
}
/* ----------------------------------------------------------------
* ExecHashTableDestroy
*
* destroy a hash table
* ----------------------------------------------------------------
*/
void
ExecHashTableDestroy(HashJoinTable hashtable)
{
int i;
/*
* Make sure all the temp files are closed. We skip batch 0, since it
* can't have any temp files (and the arrays might not even exist if
* nbatch is only 1).
*/
for (i = 1; i < hashtable->nbatch; i++)
{
if (hashtable->innerBatchFile[i])
BufFileClose(hashtable->innerBatchFile[i]);
if (hashtable->outerBatchFile[i])
BufFileClose(hashtable->outerBatchFile[i]);
}
/* Release working memory (batchCxt is a child, so it goes away too) */
MemoryContextDelete(hashtable->hashCxt);
/* And drop the control block */
pfree(hashtable);
}
/*
* ExecHashIncreaseNumBatches
* increase the original number of batches in order to reduce
* current memory consumption
*/
static void
ExecHashIncreaseNumBatches(HashJoinTable hashtable)
{
int oldnbatch = hashtable->nbatch;
int curbatch = hashtable->curbatch;
int nbatch;
int i;
MemoryContext oldcxt;
long ninmemory;
long nfreed;
/* do nothing if we've decided to shut off growth */
if (!hashtable->growEnabled)
return;
/* safety check to avoid overflow */
if (oldnbatch > INT_MAX / 2)
return;
nbatch = oldnbatch * 2;
Assert(nbatch > 1);
#ifdef HJDEBUG
printf("Increasing nbatch to %d because space = %lu\n",
nbatch, (unsigned long) hashtable->spaceUsed);
#endif
oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);
if (hashtable->innerBatchFile == NULL)
{
/* we had no file arrays before */
hashtable->innerBatchFile = (BufFile **)
palloc0(nbatch * sizeof(BufFile *));
hashtable->outerBatchFile = (BufFile **)
palloc0(nbatch * sizeof(BufFile *));
}
else
{
/* enlarge arrays and zero out added entries */
hashtable->innerBatchFile = (BufFile **)
repalloc(hashtable->innerBatchFile, nbatch * sizeof(BufFile *));
hashtable->outerBatchFile = (BufFile **)
repalloc(hashtable->outerBatchFile, nbatch * sizeof(BufFile *));
MemSet(hashtable->innerBatchFile + oldnbatch, 0,
(nbatch - oldnbatch) * sizeof(BufFile *));
MemSet(hashtable->outerBatchFile + oldnbatch, 0,
(nbatch - oldnbatch) * sizeof(BufFile *));
}
MemoryContextSwitchTo(oldcxt);
hashtable->nbatch = nbatch;
/*
* Scan through the existing hash table entries and dump out any that are
* no longer of the current batch.
*/
ninmemory = nfreed = 0;
for (i = 0; i < hashtable->nbuckets; i++)
{
HashJoinTuple prevtuple;
HashJoinTuple tuple;
prevtuple = NULL;
tuple = hashtable->buckets[i];
while (tuple != NULL)
{
/* save link in case we delete */
HashJoinTuple nexttuple = tuple->next;
int bucketno;
int batchno;
ninmemory++;
ExecHashGetBucketAndBatch(hashtable, tuple->hashvalue,
&bucketno, &batchno);
Assert(bucketno == i);
if (batchno == curbatch)
{
/* keep tuple */
prevtuple = tuple;
}
else
{
/* dump it out */
Assert(batchno > curbatch); ExecHashJoinSaveTuple(HJTUPLE_MINTUPLE(tuple),
tuple->hashvalue,
&hashtable->innerBatchFile[batchno]);
/* and remove from hash table */
if (prevtuple)
prevtuple->next = nexttuple;
else
hashtable->buckets[i] = nexttuple;
/* prevtuple doesn't change */
hashtable->spaceUsed -=
HJTUPLE_OVERHEAD + HJTUPLE_MINTUPLE(tuple)->t_len;
pfree(tuple);
nfreed++;
}
tuple = nexttuple;
}
}
#ifdef HJDEBUG
printf("Freed %ld of %ld tuples, space now %lu\n",
nfreed, ninmemory, (unsigned long) hashtable->spaceUsed);
#endif
/*
* If we dumped out either all or none of the tuples in the table, disable
* further expansion of nbatch. This situation implies that we have
* enough tuples of identical hashvalues to overflow spaceAllowed.
* Increasing nbatch will not fix it since there's no way to subdivide the
* group any more finely. We have to just gut it out and hope the server
* has enough RAM.
*/
if (nfreed == 0 || nfreed == ninmemory)
{
hashtable->growEnabled = false;
#ifdef HJDEBUG
printf("Disabling further increase of nbatch\n");
#endif
}
}
/*
* ExecHashTableInsert
* insert a tuple into the hash table depending on the hash value
* it may just go to a temp file for later batches
*
* Note: the passed TupleTableSlot may contain a regular, minimal, or virtual
* tuple; the minimal case in particular is certain to happen while reloading
* tuples from batch files. We could save some cycles in the regular-tuple
* case by not forcing the slot contents into minimal form; not clear if it's
* worth the messiness required.
*/
void
ExecHashTableInsert(HashJoinTable hashtable,
TupleTableSlot *slot,
uint32 hashvalue)
{
MinimalTuple tuple = ExecFetchSlotMinimalTuple(slot);
int bucketno;
int batchno;
ExecHashGetBucketAndBatch(hashtable, hashvalue,
&bucketno, &batchno);
/*
* decide whether to put the tuple in the hash table or a temp file
*/
if (batchno == hashtable->curbatch)
{
/* * put the tuple in hash table
*/
HashJoinTuple hashTuple;
int hashTupleSize;
hashTupleSize = HJTUPLE_OVERHEAD + tuple->t_len;
hashTuple = (HashJoinTuple) MemoryContextAlloc(hashtable->batchCxt,
hashTupleSize);
hashTuple->hashvalue = hashvalue;
memcpy(HJTUPLE_MINTUPLE(hashTuple), tuple, tuple->t_len);
hashTuple->next = hashtable->buckets[bucketno];
hashtable->buckets[bucketno] = hashTuple;
hashtable->spaceUsed += hashTupleSize;
if (hashtable->spaceUsed > hashtable->spaceAllowed)
ExecHashIncreaseNumBatches(hashtable);
}
else
{
/*
* put the tuple into a temp file for later batches
*/
Assert(batchno > hashtable->curbatch);
ExecHashJoinSaveTuple(tuple,
hashvalue,
&hashtable->innerBatchFile[batchno]);
}
}
/*
* ExecHashGetHashValue
* Compute the hash value for a tuple
*
* The tuple to be tested must be in either econtext->ecxt_outertuple or
* econtext->ecxt_innertuple. Vars in the hashkeys expressions reference
* either OUTER or INNER.
*
* A TRUE result means the tuple's hash value has been successfully computed
* and stored at *hashvalue. A FALSE result means the tuple cannot match
* because it contains a null attribute, and hence it should be discarded
* immediately. (If keep_nulls is true then FALSE is never returned.)
*/
bool
ExecHashGetHashValue(HashJoinTable hashtable,
ExprContext *econtext,
List *hashkeys,
bool outer_tuple,
bool keep_nulls,
uint32 *hashvalue)
{
uint32 hashkey = 0;
FmgrInfo *hashfunctions;
ListCell *hk;
int i = 0;
MemoryContext oldContext;
/*
* We reset the eval context each time to reclaim any memory leaked in the
* hashkey expressions.
*/
ResetExprContext(econtext);
oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
if (outer_tuple)
hashfunctions = hashtable->outer_hashfunctions;
else
hashfunctions = hashtable->inner_hashfunctions;
foreach(hk, hashkeys)
{ ExprState *keyexpr = (ExprState *) lfirst(hk);
Datum keyval;
bool isNull;
/* rotate hashkey left 1 bit at each step */
hashkey = (hashkey << 1) | ((hashkey & 0x80000000) ? 1 : 0);
/*
* Get the join attribute value of the tuple
*/
keyval = ExecEvalExpr(keyexpr, econtext, &isNull, NULL);
/*
* If the attribute is NULL, and the join operator is strict, then
* this tuple cannot pass the join qual so we can reject it
* immediately (unless we're scanning the outside of an outer join,
* in which case we must not reject it). Otherwise we act like the
* hashcode of NULL is zero (this will support operators that act like
* IS NOT DISTINCT, though not any more-random behavior). We treat
* the hash support function as strict even if the operator is not.
*
* Note: currently, all hashjoinable operators must be strict since
* the hash index AM assumes that. However, it takes so little
* extra code here to allow non-strict that we may as well do it.
*/
if (isNull)
{
if (hashtable->hashStrict[i] && !keep_nulls)
{
MemoryContextSwitchTo(oldContext);
return false; /* cannot match */
}
/* else, leave hashkey unmodified, equivalent to hashcode 0 */
}
else
{
/* Compute the hash function */
uint32 hkey;
hkey = DatumGetUInt32(FunctionCall1(&hashfunctions[i], keyval));
hashkey ^= hkey;
}
i++;
}
MemoryContextSwitchTo(oldContext);
*hashvalue = hashkey;
return true;
}
/*
* ExecHashGetBucketAndBatch
* Determine the bucket number and batch number for a hash value
*
* Note: on-the-fly increases of nbatch must not change the bucket number
* for a given hash code (since we don't move tuples to different hash
* chains), and must only cause the batch number to remain the same or
* increase. Our algorithm is
* bucketno = hashvalue MOD nbuckets
* batchno = (hashvalue DIV nbuckets) MOD nbatch
* where nbuckets and nbatch are both expected to be powers of 2, so we can
* do the computations by shifting and masking. (This assumes that all hash
* functions are good about randomizing all their output bits, else we are
* likely to have very skewed bucket or batch occupancy.)
*
* nbuckets doesn't change over the course of the join.
*
* nbatch is always a power of 2; we increase it only by doubling it. This * effectively adds one more bit to the top of the batchno.
*/
void
ExecHashGetBucketAndBatch(HashJoinTable hashtable,
uint32 hashvalue,
int *bucketno,
int *batchno)
{
uint32 nbuckets = (uint32) hashtable->nbuckets;
uint32 nbatch = (uint32) hashtable->nbatch;
if (nbatch > 1)
{
/* we can do MOD by masking, DIV by shifting */
*bucketno = hashvalue & (nbuckets - 1);
*batchno = (hashvalue >> hashtable->log2_nbuckets) & (nbatch - 1);
}
else
{
*bucketno = hashvalue & (nbuckets - 1);
*batchno = 0;
}
}
/*
* ExecScanHashBucket
* scan a hash bucket for matches to the current outer tuple
*
* The current outer tuple must be stored in econtext->ecxt_outertuple.
*/
HashJoinTuple
ExecScanHashBucket(HashJoinState *hjstate,
ExprContext *econtext)
{
List *hjclauses = hjstate->hashclauses;
HashJoinTable hashtable = hjstate->hj_HashTable;
HashJoinTuple hashTuple = hjstate->hj_CurTuple;
uint32 hashvalue = hjstate->hj_CurHashValue;
/*
* hj_CurTuple is NULL to start scanning a new bucket, or the address of
* the last tuple returned from the current bucket.
*/
if (hashTuple == NULL)
hashTuple = hashtable->buckets[hjstate->hj_CurBucketNo];
else
hashTuple = hashTuple->next;
while (hashTuple != NULL)
{
if (hashTuple->hashvalue == hashvalue)
{
TupleTableSlot *inntuple;
/* insert hashtable's tuple into exec slot so ExecQual sees it */
inntuple = ExecStoreMinimalTuple(HJTUPLE_MINTUPLE(hashTuple),
hjstate->hj_HashTupleSlot,
false); /* do not pfree */
econtext->ecxt_innertuple = inntuple;
/* reset temp memory each time to avoid leaks from qual expr */
ResetExprContext(econtext);
if (ExecQual(hjclauses, econtext, false))
{
hjstate->hj_CurTuple = hashTuple;
return hashTuple;
}
}
hashTuple = hashTuple->next;
}
/*
* no match
*/
return NULL;
}
/*
* ExecHashTableReset
*
* reset hash table header for new batch
*/
void
ExecHashTableReset(HashJoinTable hashtable)
{
MemoryContext oldcxt;
int nbuckets = hashtable->nbuckets;
/*
* Release all the hash buckets and tuples acquired in the prior pass, and
* reinitialize the context for a new pass.
*/
MemoryContextReset(hashtable->batchCxt);
oldcxt = MemoryContextSwitchTo(hashtable->batchCxt);
/* Reallocate and reinitialize the hash bucket headers. */
hashtable->buckets = (HashJoinTuple *)
palloc0(nbuckets * sizeof(HashJoinTuple));
hashtable->spaceUsed = 0;
MemoryContextSwitchTo(oldcxt);
}
void
ExecReScanHash(HashState *node, ExprContext *exprCtxt)
{
/*
* if chgParam of subnode is not null then plan will be re-scanned by
* first ExecProcNode.
*/
if (((PlanState *) node)->lefttree->chgParam == NULL)
ExecReScan(((PlanState *) node)->lefttree, exprCtxt);
}