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postgresql/src/backend/executor/nodeHash.c

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/*-------------------------------------------------------------------------
*
* nodeHash.c
* Routines to hash relations for hashjoin
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/executor/nodeHash.c
*
* See note on parallelism in nodeHashjoin.c.
*
*-------------------------------------------------------------------------
*/
/*
* 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 "access/htup_details.h"
#include "access/parallel.h"
#include "catalog/pg_statistic.h"
#include "commands/tablespace.h"
#include "executor/execdebug.h"
#include "executor/hashjoin.h"
#include "executor/nodeHash.h"
#include "executor/nodeHashjoin.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "port/atomics.h"
#include "utils/dynahash.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
static void ExecHashIncreaseNumBatches(HashJoinTable hashtable);
static void ExecHashIncreaseNumBuckets(HashJoinTable hashtable);
static void ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable);
static void ExecParallelHashIncreaseNumBuckets(HashJoinTable hashtable);
static void ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node,
int mcvsToUse);
static void ExecHashSkewTableInsert(HashJoinTable hashtable,
TupleTableSlot *slot,
uint32 hashvalue,
int bucketNumber);
static void ExecHashRemoveNextSkewBucket(HashJoinTable hashtable);
static void *dense_alloc(HashJoinTable hashtable, Size size);
static HashJoinTuple ExecParallelHashTupleAlloc(HashJoinTable hashtable,
size_t size,
dsa_pointer *shared);
static void MultiExecPrivateHash(HashState *node);
static void MultiExecParallelHash(HashState *node);
static inline HashJoinTuple ExecParallelHashFirstTuple(HashJoinTable table,
int bucketno);
static inline HashJoinTuple ExecParallelHashNextTuple(HashJoinTable table,
HashJoinTuple tuple);
static inline void ExecParallelHashPushTuple(dsa_pointer_atomic *head,
HashJoinTuple tuple,
dsa_pointer tuple_shared);
static void ExecParallelHashJoinSetUpBatches(HashJoinTable hashtable, int nbatch);
static void ExecParallelHashEnsureBatchAccessors(HashJoinTable hashtable);
static void ExecParallelHashRepartitionFirst(HashJoinTable hashtable);
static void ExecParallelHashRepartitionRest(HashJoinTable hashtable);
static HashMemoryChunk ExecParallelHashPopChunkQueue(HashJoinTable table,
dsa_pointer *shared);
static bool ExecParallelHashTuplePrealloc(HashJoinTable hashtable,
int batchno,
size_t size);
static void ExecParallelHashMergeCounters(HashJoinTable hashtable);
static void ExecParallelHashCloseBatchAccessors(HashJoinTable hashtable);
/* ----------------------------------------------------------------
* ExecHash
*
* stub for pro forma compliance
* ----------------------------------------------------------------
*/
static TupleTableSlot *
ExecHash(PlanState *pstate)
{
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)
{
/* must provide our own instrumentation support */
if (node->ps.instrument)
InstrStartNode(node->ps.instrument);
if (node->parallel_state != NULL)
MultiExecParallelHash(node);
else
MultiExecPrivateHash(node);
/* must provide our own instrumentation support */
if (node->ps.instrument)
InstrStopNode(node->ps.instrument, node->hashtable->partialTuples);
/*
* 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;
}
/* ----------------------------------------------------------------
* MultiExecPrivateHash
*
* parallel-oblivious version, building a backend-private
* hash table and (if necessary) batch files.
* ----------------------------------------------------------------
*/
static void
MultiExecPrivateHash(HashState *node)
{
PlanState *outerNode;
List *hashkeys;
HashJoinTable hashtable;
TupleTableSlot *slot;
ExprContext *econtext;
uint32 hashvalue;
/*
* get state info from node
*/
outerNode = outerPlanState(node);
hashtable = node->hashtable;
/*
* set expression context
*/
hashkeys = node->hashkeys;
econtext = node->ps.ps_ExprContext;
/*
* Get all tuples from the node below the Hash node 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_outertuple = slot;
if (ExecHashGetHashValue(hashtable, econtext, hashkeys,
false, hashtable->keepNulls,
&hashvalue))
{
int bucketNumber;
bucketNumber = ExecHashGetSkewBucket(hashtable, hashvalue);
if (bucketNumber != INVALID_SKEW_BUCKET_NO)
{
/* It's a skew tuple, so put it into that hash table */
ExecHashSkewTableInsert(hashtable, slot, hashvalue,
bucketNumber);
hashtable->skewTuples += 1;
}
else
{
/* Not subject to skew optimization, so insert normally */
ExecHashTableInsert(hashtable, slot, hashvalue);
}
hashtable->totalTuples += 1;
}
}
/* resize the hash table if needed (NTUP_PER_BUCKET exceeded) */
if (hashtable->nbuckets != hashtable->nbuckets_optimal)
ExecHashIncreaseNumBuckets(hashtable);
/* Account for the buckets in spaceUsed (reported in EXPLAIN ANALYZE) */
hashtable->spaceUsed += hashtable->nbuckets * sizeof(HashJoinTuple);
if (hashtable->spaceUsed > hashtable->spacePeak)
hashtable->spacePeak = hashtable->spaceUsed;
hashtable->partialTuples = hashtable->totalTuples;
}
/* ----------------------------------------------------------------
* MultiExecParallelHash
*
* parallel-aware version, building a shared hash table and
* (if necessary) batch files using the combined effort of
* a set of co-operating backends.
* ----------------------------------------------------------------
*/
static void
MultiExecParallelHash(HashState *node)
{
ParallelHashJoinState *pstate;
PlanState *outerNode;
List *hashkeys;
HashJoinTable hashtable;
TupleTableSlot *slot;
ExprContext *econtext;
uint32 hashvalue;
Barrier *build_barrier;
int i;
/*
* get state info from node
*/
outerNode = outerPlanState(node);
hashtable = node->hashtable;
/*
* set expression context
*/
hashkeys = node->hashkeys;
econtext = node->ps.ps_ExprContext;
/*
* Synchronize the parallel hash table build. At this stage we know that
* the shared hash table has been or is being set up by
* ExecHashTableCreate(), but we don't know if our peers have returned
* from there or are here in MultiExecParallelHash(), and if so how far
* through they are. To find out, we check the build_barrier phase then
* and jump to the right step in the build algorithm.
*/
pstate = hashtable->parallel_state;
build_barrier = &pstate->build_barrier;
Assert(BarrierPhase(build_barrier) >= PHJ_BUILD_ALLOCATING);
switch (BarrierPhase(build_barrier))
{
case PHJ_BUILD_ALLOCATING:
/*
* Either I just allocated the initial hash table in
* ExecHashTableCreate(), or someone else is doing that. Either
* way, wait for everyone to arrive here so we can proceed.
*/
BarrierArriveAndWait(build_barrier, WAIT_EVENT_HASH_BUILD_ALLOCATING);
/* Fall through. */
case PHJ_BUILD_HASHING_INNER:
/*
* It's time to begin hashing, or if we just arrived here then
* hashing is already underway, so join in that effort. While
* hashing we have to be prepared to help increase the number of
* batches or buckets at any time, and if we arrived here when
* that was already underway we'll have to help complete that work
* immediately so that it's safe to access batches and buckets
* below.
*/
if (PHJ_GROW_BATCHES_PHASE(BarrierAttach(&pstate->grow_batches_barrier)) !=
PHJ_GROW_BATCHES_ELECTING)
ExecParallelHashIncreaseNumBatches(hashtable);
if (PHJ_GROW_BUCKETS_PHASE(BarrierAttach(&pstate->grow_buckets_barrier)) !=
PHJ_GROW_BUCKETS_ELECTING)
ExecParallelHashIncreaseNumBuckets(hashtable);
ExecParallelHashEnsureBatchAccessors(hashtable);
ExecParallelHashTableSetCurrentBatch(hashtable, 0);
for (;;)
{
slot = ExecProcNode(outerNode);
if (TupIsNull(slot))
break;
econtext->ecxt_outertuple = slot;
if (ExecHashGetHashValue(hashtable, econtext, hashkeys,
false, hashtable->keepNulls,
&hashvalue))
ExecParallelHashTableInsert(hashtable, slot, hashvalue);
hashtable->partialTuples++;
}
/*
* Make sure that any tuples we wrote to disk are visible to
* others before anyone tries to load them.
*/
for (i = 0; i < hashtable->nbatch; ++i)
sts_end_write(hashtable->batches[i].inner_tuples);
/*
* Update shared counters. We need an accurate total tuple count
* to control the empty table optimization.
*/
ExecParallelHashMergeCounters(hashtable);
BarrierDetach(&pstate->grow_buckets_barrier);
BarrierDetach(&pstate->grow_batches_barrier);
/*
* Wait for everyone to finish building and flushing files and
* counters.
*/
if (BarrierArriveAndWait(build_barrier,
WAIT_EVENT_HASH_BUILD_HASHING_INNER))
{
/*
* Elect one backend to disable any further growth. Batches
* are now fixed. While building them we made sure they'd fit
* in our memory budget when we load them back in later (or we
* tried to do that and gave up because we detected extreme
* skew).
*/
pstate->growth = PHJ_GROWTH_DISABLED;
}
}
/*
* We're not yet attached to a batch. We all agree on the dimensions and
* number of inner tuples (for the empty table optimization).
*/
hashtable->curbatch = -1;
hashtable->nbuckets = pstate->nbuckets;
hashtable->log2_nbuckets = my_log2(hashtable->nbuckets);
hashtable->totalTuples = pstate->total_tuples;
ExecParallelHashEnsureBatchAccessors(hashtable);
/*
* The next synchronization point is in ExecHashJoin's HJ_BUILD_HASHTABLE
* case, which will bring the build phase to PHJ_BUILD_DONE (if it isn't
* there already).
*/
Assert(BarrierPhase(build_barrier) == PHJ_BUILD_HASHING_OUTER ||
BarrierPhase(build_barrier) == PHJ_BUILD_DONE);
}
/* ----------------------------------------------------------------
* 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->ps.ExecProcNode = ExecHash;
hashstate->hashtable = NULL;
hashstate->hashkeys = NIL; /* will be set by parent HashJoin */
/*
* Miscellaneous initialization
*
* create expression context for node
*/
ExecAssignExprContext(estate, &hashstate->ps);
/*
* initialize child nodes
*/
outerPlanState(hashstate) = ExecInitNode(outerPlan(node), estate, eflags);
/*
* initialize our result slot and type. No need to build projection
* because this node doesn't do projections.
*/
ExecInitResultTupleSlotTL(&hashstate->ps, &TTSOpsMinimalTuple);
hashstate->ps.ps_ProjInfo = NULL;
/*
* initialize child expressions
*/
Assert(node->plan.qual == NIL);
hashstate->hashkeys =
ExecInitExprList(node->hashkeys, (PlanState *) hashstate);
return hashstate;
}
/* ---------------------------------------------------------------
* 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(HashState *state, List *hashOperators, List *hashCollations, bool keepNulls)
{
Hash *node;
HashJoinTable hashtable;
Plan *outerNode;
size_t space_allowed;
int nbuckets;
int nbatch;
double rows;
int num_skew_mcvs;
int log2_nbuckets;
int nkeys;
int i;
ListCell *ho;
ListCell *hc;
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.
*/
node = (Hash *) state->ps.plan;
outerNode = outerPlan(node);
/*
* If this is shared hash table with a partial plan, then we can't use
* outerNode->plan_rows to estimate its size. We need an estimate of the
* total number of rows across all copies of the partial plan.
*/
rows = node->plan.parallel_aware ? node->rows_total : outerNode->plan_rows;
ExecChooseHashTableSize(rows, outerNode->plan_width,
OidIsValid(node->skewTable),
state->parallel_state != NULL,
state->parallel_state != NULL ?
state->parallel_state->nparticipants - 1 : 0,
&space_allowed,
&nbuckets, &nbatch, &num_skew_mcvs);
/* 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. Everything else should be kept inside the
* subsidiary hashCxt or batchCxt.
*/
hashtable = (HashJoinTable) palloc(sizeof(HashJoinTableData));
hashtable->nbuckets = nbuckets;
hashtable->nbuckets_original = nbuckets;
hashtable->nbuckets_optimal = nbuckets;
hashtable->log2_nbuckets = log2_nbuckets;
hashtable->log2_nbuckets_optimal = log2_nbuckets;
hashtable->buckets.unshared = NULL;
hashtable->keepNulls = keepNulls;
hashtable->skewEnabled = false;
hashtable->skewBucket = NULL;
hashtable->skewBucketLen = 0;
hashtable->nSkewBuckets = 0;
hashtable->skewBucketNums = NULL;
hashtable->nbatch = nbatch;
hashtable->curbatch = 0;
hashtable->nbatch_original = nbatch;
hashtable->nbatch_outstart = nbatch;
hashtable->growEnabled = true;
hashtable->totalTuples = 0;
hashtable->partialTuples = 0;
hashtable->skewTuples = 0;
hashtable->innerBatchFile = NULL;
hashtable->outerBatchFile = NULL;
hashtable->spaceUsed = 0;
hashtable->spacePeak = 0;
hashtable->spaceAllowed = space_allowed;
hashtable->spaceUsedSkew = 0;
hashtable->spaceAllowedSkew =
hashtable->spaceAllowed * SKEW_WORK_MEM_PERCENT / 100;
hashtable->chunks = NULL;
hashtable->current_chunk = NULL;
hashtable->parallel_state = state->parallel_state;
hashtable->area = state->ps.state->es_query_dsa;
hashtable->batches = NULL;
#ifdef HJDEBUG
printf("Hashjoin %p: initial nbatch = %d, nbuckets = %d\n",
hashtable, nbatch, nbuckets);
#endif
/*
* 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_SIZES);
hashtable->batchCxt = AllocSetContextCreate(hashtable->hashCxt,
"HashBatchContext",
ALLOCSET_DEFAULT_SIZES);
/* Allocate data that will live for the life of the hashjoin */
oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);
/*
* 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));
hashtable->collations = (Oid *) palloc(nkeys * sizeof(Oid));
i = 0;
forboth(ho, hashOperators, hc, hashCollations)
{
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);
hashtable->collations[i] = lfirst_oid(hc);
i++;
}
if (nbatch > 1 && hashtable->parallel_state == NULL)
{
/*
* allocate and initialize the file arrays in hashCxt (not needed for
* parallel case which uses shared tuplestores instead of raw files)
*/
hashtable->innerBatchFile = (BufFile **)
palloc0(nbatch * sizeof(BufFile *));
hashtable->outerBatchFile = (BufFile **)
palloc0(nbatch * sizeof(BufFile *));
/* The files will not be opened until needed... */
/* ... but make sure we have temp tablespaces established for them */
PrepareTempTablespaces();
}
MemoryContextSwitchTo(oldcxt);
if (hashtable->parallel_state)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
Barrier *build_barrier;
/*
* Attach to the build barrier. The corresponding detach operation is
* in ExecHashTableDetach. Note that we won't attach to the
* batch_barrier for batch 0 yet. We'll attach later and start it out
* in PHJ_BATCH_PROBING phase, because batch 0 is allocated up front
* and then loaded while hashing (the standard hybrid hash join
* algorithm), and we'll coordinate that using build_barrier.
*/
build_barrier = &pstate->build_barrier;
BarrierAttach(build_barrier);
/*
* So far we have no idea whether there are any other participants,
* and if so, what phase they are working on. The only thing we care
* about at this point is whether someone has already created the
* SharedHashJoinBatch objects and the hash table for batch 0. One
* backend will be elected to do that now if necessary.
*/
if (BarrierPhase(build_barrier) == PHJ_BUILD_ELECTING &&
BarrierArriveAndWait(build_barrier, WAIT_EVENT_HASH_BUILD_ELECTING))
{
pstate->nbatch = nbatch;
pstate->space_allowed = space_allowed;
pstate->growth = PHJ_GROWTH_OK;
/* Set up the shared state for coordinating batches. */
ExecParallelHashJoinSetUpBatches(hashtable, nbatch);
/*
* Allocate batch 0's hash table up front so we can load it
* directly while hashing.
*/
pstate->nbuckets = nbuckets;
ExecParallelHashTableAlloc(hashtable, 0);
}
/*
* The next Parallel Hash synchronization point is in
* MultiExecParallelHash(), which will progress it all the way to
* PHJ_BUILD_DONE. The caller must not return control from this
* executor node between now and then.
*/
}
else
{
/*
* Prepare context for the first-scan space allocations; allocate the
* hashbucket array therein, and set each bucket "empty".
*/
MemoryContextSwitchTo(hashtable->batchCxt);
hashtable->buckets.unshared = (HashJoinTuple *)
palloc0(nbuckets * sizeof(HashJoinTuple));
/*
* Set up for skew optimization, if possible and there's a need for
* more than one batch. (In a one-batch join, there's no point in
* it.)
*/
if (nbatch > 1)
ExecHashBuildSkewHash(hashtable, node, num_skew_mcvs);
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 1
void
ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
bool try_combined_work_mem,
int parallel_workers,
size_t *space_allowed,
int *numbuckets,
int *numbatches,
int *num_skew_mcvs)
{
int tupsize;
double inner_rel_bytes;
long bucket_bytes;
long hash_table_bytes;
long skew_table_bytes;
long max_pointers;
long mppow2;
int nbatch = 1;
int nbuckets;
double dbuckets;
/* 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(SizeofMinimalTupleHeader) +
MAXALIGN(tupwidth);
inner_rel_bytes = ntuples * tupsize;
/*
* Target in-memory hashtable size is work_mem kilobytes.
*/
hash_table_bytes = work_mem * 1024L;
/*
* Parallel Hash tries to use the combined work_mem of all workers to
* avoid the need to batch. If that won't work, it falls back to work_mem
* per worker and tries to process batches in parallel.
*/
if (try_combined_work_mem)
hash_table_bytes += hash_table_bytes * parallel_workers;
*space_allowed = hash_table_bytes;
/*
* If skew optimization is possible, estimate the number of skew buckets
* that will fit in the memory allowed, and decrement the assumed space
* available for the main hash table accordingly.
*
* We make the optimistic assumption that each skew bucket will contain
* one inner-relation tuple. If that turns out to be low, we will recover
* at runtime by reducing the number of skew buckets.
*
* hashtable->skewBucket will have up to 8 times as many HashSkewBucket
* pointers as the number of MCVs we allow, since ExecHashBuildSkewHash
* will round up to the next power of 2 and then multiply by 4 to reduce
* collisions.
*/
if (useskew)
{
skew_table_bytes = hash_table_bytes * SKEW_WORK_MEM_PERCENT / 100;
/*----------
* Divisor is:
* size of a hash tuple +
* worst-case size of skewBucket[] per MCV +
* size of skewBucketNums[] entry +
* size of skew bucket struct itself
*----------
*/
*num_skew_mcvs = skew_table_bytes / (tupsize +
(8 * sizeof(HashSkewBucket *)) +
sizeof(int) +
SKEW_BUCKET_OVERHEAD);
if (*num_skew_mcvs > 0)
hash_table_bytes -= skew_table_bytes;
}
else
*num_skew_mcvs = 0;
/*
* Set nbuckets to achieve an average bucket load of NTUP_PER_BUCKET when
* memory is filled, assuming a single batch; but limit the value so that
* the pointer arrays we'll try to allocate do not exceed work_mem nor
* MaxAllocSize.
*
* Note that both nbuckets and nbatch must be powers of 2 to make
* ExecHashGetBucketAndBatch fast.
*/
max_pointers = *space_allowed / sizeof(HashJoinTuple);
max_pointers = Min(max_pointers, MaxAllocSize / sizeof(HashJoinTuple));
/* If max_pointers isn't a power of 2, must round it down to one */
mppow2 = 1L << my_log2(max_pointers);
if (max_pointers != mppow2)
max_pointers = mppow2 / 2;
/* Also ensure we avoid integer overflow in nbatch and nbuckets */
/* (this step is redundant given the current value of MaxAllocSize) */
max_pointers = Min(max_pointers, INT_MAX / 2);
dbuckets = ceil(ntuples / NTUP_PER_BUCKET);
dbuckets = Min(dbuckets, max_pointers);
nbuckets = (int) dbuckets;
/* don't let nbuckets be really small, though ... */
nbuckets = Max(nbuckets, 1024);
/* ... and force it to be a power of 2. */
nbuckets = 1 << my_log2(nbuckets);
/*
* If there's not enough space to store the projected number of tuples and
* the required bucket headers, we will need multiple batches.
*/
bucket_bytes = sizeof(HashJoinTuple) * nbuckets;
if (inner_rel_bytes + bucket_bytes > hash_table_bytes)
{
/* We'll need multiple batches */
long lbuckets;
double dbatch;
int minbatch;
long bucket_size;
/*
* If Parallel Hash with combined work_mem would still need multiple
* batches, we'll have to fall back to regular work_mem budget.
*/
if (try_combined_work_mem)
{
ExecChooseHashTableSize(ntuples, tupwidth, useskew,
false, parallel_workers,
space_allowed,
numbuckets,
numbatches,
num_skew_mcvs);
return;
}
/*
* Estimate the number of buckets we'll want to have when work_mem is
* entirely full. Each bucket will contain a bucket pointer plus
* NTUP_PER_BUCKET tuples, whose projected size already includes
* overhead for the hash code, pointer to the next tuple, etc.
*/
bucket_size = (tupsize * NTUP_PER_BUCKET + sizeof(HashJoinTuple));
lbuckets = 1L << my_log2(hash_table_bytes / bucket_size);
lbuckets = Min(lbuckets, max_pointers);
nbuckets = (int) lbuckets;
nbuckets = 1 << my_log2(nbuckets);
bucket_bytes = nbuckets * sizeof(HashJoinTuple);
/*
* Buckets are simple pointers to hashjoin tuples, while tupsize
* includes the pointer, hash code, and MinimalTupleData. So buckets
* should never really exceed 25% of work_mem (even for
* NTUP_PER_BUCKET=1); except maybe for work_mem values that are not
* 2^N bytes, where we might get more because of doubling. So let's
* look for 50% here.
*/
Assert(bucket_bytes <= hash_table_bytes / 2);
/* Calculate required number of batches. */
dbatch = ceil(inner_rel_bytes / (hash_table_bytes - bucket_bytes));
dbatch = Min(dbatch, max_pointers);
minbatch = (int) dbatch;
nbatch = 2;
while (nbatch < minbatch)
nbatch <<= 1;
}
Assert(nbuckets > 0);
Assert(nbatch > 0);
*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). Parallel hash joins don't use these files.
*/
if (hashtable->innerBatchFile != NULL)
{
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;
MemoryContext oldcxt;
long ninmemory;
long nfreed;
HashMemoryChunk oldchunks;
/* do nothing if we've decided to shut off growth */
if (!hashtable->growEnabled)
return;
/* safety check to avoid overflow */
if (oldnbatch > Min(INT_MAX / 2, MaxAllocSize / (sizeof(void *) * 2)))
return;
nbatch = oldnbatch * 2;
Assert(nbatch > 1);
#ifdef HJDEBUG
printf("Hashjoin %p: increasing nbatch to %d because space = %zu\n",
hashtable, nbatch, 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 *));
/* time to establish the temp tablespaces, too */
PrepareTempTablespaces();
}
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;
/* If know we need to resize nbuckets, we can do it while rebatching. */
if (hashtable->nbuckets_optimal != hashtable->nbuckets)
{
/* we never decrease the number of buckets */
Assert(hashtable->nbuckets_optimal > hashtable->nbuckets);
hashtable->nbuckets = hashtable->nbuckets_optimal;
hashtable->log2_nbuckets = hashtable->log2_nbuckets_optimal;
hashtable->buckets.unshared =
repalloc(hashtable->buckets.unshared,
sizeof(HashJoinTuple) * hashtable->nbuckets);
}
/*
* We will scan through the chunks directly, so that we can reset the
* buckets now and not have to keep track which tuples in the buckets have
* already been processed. We will free the old chunks as we go.
*/
memset(hashtable->buckets.unshared, 0,
sizeof(HashJoinTuple) * hashtable->nbuckets);
oldchunks = hashtable->chunks;
hashtable->chunks = NULL;
/* so, let's scan through the old chunks, and all tuples in each chunk */
while (oldchunks != NULL)
{
HashMemoryChunk nextchunk = oldchunks->next.unshared;
/* position within the buffer (up to oldchunks->used) */
size_t idx = 0;
/* process all tuples stored in this chunk (and then free it) */
while (idx < oldchunks->used)
{
HashJoinTuple hashTuple = (HashJoinTuple) (HASH_CHUNK_DATA(oldchunks) + idx);
MinimalTuple tuple = HJTUPLE_MINTUPLE(hashTuple);
int hashTupleSize = (HJTUPLE_OVERHEAD + tuple->t_len);
int bucketno;
int batchno;
ninmemory++;
ExecHashGetBucketAndBatch(hashtable, hashTuple->hashvalue,
&bucketno, &batchno);
if (batchno == curbatch)
{
/* keep tuple in memory - copy it into the new chunk */
HashJoinTuple copyTuple;
copyTuple = (HashJoinTuple) dense_alloc(hashtable, hashTupleSize);
memcpy(copyTuple, hashTuple, hashTupleSize);
/* and add it back to the appropriate bucket */
copyTuple->next.unshared = hashtable->buckets.unshared[bucketno];
hashtable->buckets.unshared[bucketno] = copyTuple;
}
else
{
/* dump it out */
Assert(batchno > curbatch);
ExecHashJoinSaveTuple(HJTUPLE_MINTUPLE(hashTuple),
hashTuple->hashvalue,
&hashtable->innerBatchFile[batchno]);
hashtable->spaceUsed -= hashTupleSize;
nfreed++;
}
/* next tuple in this chunk */
idx += MAXALIGN(hashTupleSize);
/* allow this loop to be cancellable */
CHECK_FOR_INTERRUPTS();
}
/* we're done with this chunk - free it and proceed to the next one */
pfree(oldchunks);
oldchunks = nextchunk;
}
#ifdef HJDEBUG
printf("Hashjoin %p: freed %ld of %ld tuples, space now %zu\n",
hashtable, nfreed, ninmemory, 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("Hashjoin %p: disabling further increase of nbatch\n",
hashtable);
#endif
}
}
/*
* ExecParallelHashIncreaseNumBatches
* Every participant attached to grow_batches_barrier must run this
* function when it observes growth == PHJ_GROWTH_NEED_MORE_BATCHES.
*/
static void
ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
int i;
Assert(BarrierPhase(&pstate->build_barrier) == PHJ_BUILD_HASHING_INNER);
/*
* It's unlikely, but we need to be prepared for new participants to show
* up while we're in the middle of this operation so we need to switch on
* barrier phase here.
*/
switch (PHJ_GROW_BATCHES_PHASE(BarrierPhase(&pstate->grow_batches_barrier)))
{
case PHJ_GROW_BATCHES_ELECTING:
/*
* Elect one participant to prepare to grow the number of batches.
* This involves reallocating or resetting the buckets of batch 0
* in preparation for all participants to begin repartitioning the
* tuples.
*/
if (BarrierArriveAndWait(&pstate->grow_batches_barrier,
WAIT_EVENT_HASH_GROW_BATCHES_ELECTING))
{
dsa_pointer_atomic *buckets;
ParallelHashJoinBatch *old_batch0;
int new_nbatch;
int i;
/* Move the old batch out of the way. */
old_batch0 = hashtable->batches[0].shared;
pstate->old_batches = pstate->batches;
pstate->old_nbatch = hashtable->nbatch;
pstate->batches = InvalidDsaPointer;
/* Free this backend's old accessors. */
ExecParallelHashCloseBatchAccessors(hashtable);
/* Figure out how many batches to use. */
if (hashtable->nbatch == 1)
{
/*
* We are going from single-batch to multi-batch. We need
* to switch from one large combined memory budget to the
* regular work_mem budget.
*/
pstate->space_allowed = work_mem * 1024L;
/*
* The combined work_mem of all participants wasn't
* enough. Therefore one batch per participant would be
* approximately equivalent and would probably also be
* insufficient. So try two batches per participant,
* rounded up to a power of two.
*/
new_nbatch = 1 << my_log2(pstate->nparticipants * 2);
}
else
{
/*
* We were already multi-batched. Try doubling the number
* of batches.
*/
new_nbatch = hashtable->nbatch * 2;
}
/* Allocate new larger generation of batches. */
Assert(hashtable->nbatch == pstate->nbatch);
ExecParallelHashJoinSetUpBatches(hashtable, new_nbatch);
Assert(hashtable->nbatch == pstate->nbatch);
/* Replace or recycle batch 0's bucket array. */
if (pstate->old_nbatch == 1)
{
double dtuples;
double dbuckets;
int new_nbuckets;
/*
* We probably also need a smaller bucket array. How many
* tuples do we expect per batch, assuming we have only
* half of them so far? Normally we don't need to change
* the bucket array's size, because the size of each batch
* stays the same as we add more batches, but in this
* special case we move from a large batch to many smaller
* batches and it would be wasteful to keep the large
* array.
*/
dtuples = (old_batch0->ntuples * 2.0) / new_nbatch;
dbuckets = ceil(dtuples / NTUP_PER_BUCKET);
dbuckets = Min(dbuckets,
MaxAllocSize / sizeof(dsa_pointer_atomic));
new_nbuckets = (int) dbuckets;
new_nbuckets = Max(new_nbuckets, 1024);
new_nbuckets = 1 << my_log2(new_nbuckets);
dsa_free(hashtable->area, old_batch0->buckets);
hashtable->batches[0].shared->buckets =
dsa_allocate(hashtable->area,
sizeof(dsa_pointer_atomic) * new_nbuckets);
buckets = (dsa_pointer_atomic *)
dsa_get_address(hashtable->area,
hashtable->batches[0].shared->buckets);
for (i = 0; i < new_nbuckets; ++i)
dsa_pointer_atomic_init(&buckets[i], InvalidDsaPointer);
pstate->nbuckets = new_nbuckets;
}
else
{
/* Recycle the existing bucket array. */
hashtable->batches[0].shared->buckets = old_batch0->buckets;
buckets = (dsa_pointer_atomic *)
dsa_get_address(hashtable->area, old_batch0->buckets);
for (i = 0; i < hashtable->nbuckets; ++i)
dsa_pointer_atomic_write(&buckets[i], InvalidDsaPointer);
}
/* Move all chunks to the work queue for parallel processing. */
pstate->chunk_work_queue = old_batch0->chunks;
/* Disable further growth temporarily while we're growing. */
pstate->growth = PHJ_GROWTH_DISABLED;
}
else
{
/* All other participants just flush their tuples to disk. */
ExecParallelHashCloseBatchAccessors(hashtable);
}
/* Fall through. */
case PHJ_GROW_BATCHES_ALLOCATING:
/* Wait for the above to be finished. */
BarrierArriveAndWait(&pstate->grow_batches_barrier,
WAIT_EVENT_HASH_GROW_BATCHES_ALLOCATING);
/* Fall through. */
case PHJ_GROW_BATCHES_REPARTITIONING:
/* Make sure that we have the current dimensions and buckets. */
ExecParallelHashEnsureBatchAccessors(hashtable);
ExecParallelHashTableSetCurrentBatch(hashtable, 0);
/* Then partition, flush counters. */
ExecParallelHashRepartitionFirst(hashtable);
ExecParallelHashRepartitionRest(hashtable);
ExecParallelHashMergeCounters(hashtable);
/* Wait for the above to be finished. */
BarrierArriveAndWait(&pstate->grow_batches_barrier,
WAIT_EVENT_HASH_GROW_BATCHES_REPARTITIONING);
/* Fall through. */
case PHJ_GROW_BATCHES_DECIDING:
/*
* Elect one participant to clean up and decide whether further
* repartitioning is needed, or should be disabled because it's
* not helping.
*/
if (BarrierArriveAndWait(&pstate->grow_batches_barrier,
WAIT_EVENT_HASH_GROW_BATCHES_DECIDING))
{
bool space_exhausted = false;
bool extreme_skew_detected = false;
/* Make sure that we have the current dimensions and buckets. */
ExecParallelHashEnsureBatchAccessors(hashtable);
ExecParallelHashTableSetCurrentBatch(hashtable, 0);
/* Are any of the new generation of batches exhausted? */
for (i = 0; i < hashtable->nbatch; ++i)
{
ParallelHashJoinBatch *batch = hashtable->batches[i].shared;
if (batch->space_exhausted ||
batch->estimated_size > pstate->space_allowed)
{
int parent;
space_exhausted = true;
/*
* Did this batch receive ALL of the tuples from its
* parent batch? That would indicate that further
* repartitioning isn't going to help (the hash values
* are probably all the same).
*/
parent = i % pstate->old_nbatch;
if (batch->ntuples == hashtable->batches[parent].shared->old_ntuples)
extreme_skew_detected = true;
}
}
/* Don't keep growing if it's not helping or we'd overflow. */
if (extreme_skew_detected || hashtable->nbatch >= INT_MAX / 2)
pstate->growth = PHJ_GROWTH_DISABLED;
else if (space_exhausted)
pstate->growth = PHJ_GROWTH_NEED_MORE_BATCHES;
else
pstate->growth = PHJ_GROWTH_OK;
/* Free the old batches in shared memory. */
dsa_free(hashtable->area, pstate->old_batches);
pstate->old_batches = InvalidDsaPointer;
}
/* Fall through. */
case PHJ_GROW_BATCHES_FINISHING:
/* Wait for the above to complete. */
BarrierArriveAndWait(&pstate->grow_batches_barrier,
WAIT_EVENT_HASH_GROW_BATCHES_FINISHING);
}
}
/*
* Repartition the tuples currently loaded into memory for inner batch 0
* because the number of batches has been increased. Some tuples are retained
* in memory and some are written out to a later batch.
*/
static void
ExecParallelHashRepartitionFirst(HashJoinTable hashtable)
{
dsa_pointer chunk_shared;
HashMemoryChunk chunk;
Assert(hashtable->nbatch == hashtable->parallel_state->nbatch);
while ((chunk = ExecParallelHashPopChunkQueue(hashtable, &chunk_shared)))
{
size_t idx = 0;
/* Repartition all tuples in this chunk. */
while (idx < chunk->used)
{
HashJoinTuple hashTuple = (HashJoinTuple) (HASH_CHUNK_DATA(chunk) + idx);
MinimalTuple tuple = HJTUPLE_MINTUPLE(hashTuple);
HashJoinTuple copyTuple;
dsa_pointer shared;
int bucketno;
int batchno;
ExecHashGetBucketAndBatch(hashtable, hashTuple->hashvalue,
&bucketno, &batchno);
Assert(batchno < hashtable->nbatch);
if (batchno == 0)
{
/* It still belongs in batch 0. Copy to a new chunk. */
copyTuple =
ExecParallelHashTupleAlloc(hashtable,
HJTUPLE_OVERHEAD + tuple->t_len,
&shared);
copyTuple->hashvalue = hashTuple->hashvalue;
memcpy(HJTUPLE_MINTUPLE(copyTuple), tuple, tuple->t_len);
ExecParallelHashPushTuple(&hashtable->buckets.shared[bucketno],
copyTuple, shared);
}
else
{
size_t tuple_size =
MAXALIGN(HJTUPLE_OVERHEAD + tuple->t_len);
/* It belongs in a later batch. */
hashtable->batches[batchno].estimated_size += tuple_size;
sts_puttuple(hashtable->batches[batchno].inner_tuples,
&hashTuple->hashvalue, tuple);
}
/* Count this tuple. */
++hashtable->batches[0].old_ntuples;
++hashtable->batches[batchno].ntuples;
idx += MAXALIGN(HJTUPLE_OVERHEAD +
HJTUPLE_MINTUPLE(hashTuple)->t_len);
}
/* Free this chunk. */
dsa_free(hashtable->area, chunk_shared);
CHECK_FOR_INTERRUPTS();
}
}
/*
* Help repartition inner batches 1..n.
*/
static void
ExecParallelHashRepartitionRest(HashJoinTable hashtable)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
int old_nbatch = pstate->old_nbatch;
SharedTuplestoreAccessor **old_inner_tuples;
ParallelHashJoinBatch *old_batches;
int i;
/* Get our hands on the previous generation of batches. */
old_batches = (ParallelHashJoinBatch *)
dsa_get_address(hashtable->area, pstate->old_batches);
old_inner_tuples = palloc0(sizeof(SharedTuplestoreAccessor *) * old_nbatch);
for (i = 1; i < old_nbatch; ++i)
{
ParallelHashJoinBatch *shared =
NthParallelHashJoinBatch(old_batches, i);
old_inner_tuples[i] = sts_attach(ParallelHashJoinBatchInner(shared),
ParallelWorkerNumber + 1,
&pstate->fileset);
}
/* Join in the effort to repartition them. */
for (i = 1; i < old_nbatch; ++i)
{
MinimalTuple tuple;
uint32 hashvalue;
/* Scan one partition from the previous generation. */
sts_begin_parallel_scan(old_inner_tuples[i]);
while ((tuple = sts_parallel_scan_next(old_inner_tuples[i], &hashvalue)))
{
size_t tuple_size = MAXALIGN(HJTUPLE_OVERHEAD + tuple->t_len);
int bucketno;
int batchno;
/* Decide which partition it goes to in the new generation. */
ExecHashGetBucketAndBatch(hashtable, hashvalue, &bucketno,
&batchno);
hashtable->batches[batchno].estimated_size += tuple_size;
++hashtable->batches[batchno].ntuples;
++hashtable->batches[i].old_ntuples;
/* Store the tuple its new batch. */
sts_puttuple(hashtable->batches[batchno].inner_tuples,
&hashvalue, tuple);
CHECK_FOR_INTERRUPTS();
}
sts_end_parallel_scan(old_inner_tuples[i]);
}
pfree(old_inner_tuples);
}
/*
* Transfer the backend-local per-batch counters to the shared totals.
*/
static void
ExecParallelHashMergeCounters(HashJoinTable hashtable)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
int i;
LWLockAcquire(&pstate->lock, LW_EXCLUSIVE);
pstate->total_tuples = 0;
for (i = 0; i < hashtable->nbatch; ++i)
{
ParallelHashJoinBatchAccessor *batch = &hashtable->batches[i];
batch->shared->size += batch->size;
batch->shared->estimated_size += batch->estimated_size;
batch->shared->ntuples += batch->ntuples;
batch->shared->old_ntuples += batch->old_ntuples;
batch->size = 0;
batch->estimated_size = 0;
batch->ntuples = 0;
batch->old_ntuples = 0;
pstate->total_tuples += batch->shared->ntuples;
}
LWLockRelease(&pstate->lock);
}
/*
* ExecHashIncreaseNumBuckets
* increase the original number of buckets in order to reduce
* number of tuples per bucket
*/
static void
ExecHashIncreaseNumBuckets(HashJoinTable hashtable)
{
HashMemoryChunk chunk;
/* do nothing if not an increase (it's called increase for a reason) */
if (hashtable->nbuckets >= hashtable->nbuckets_optimal)
return;
#ifdef HJDEBUG
printf("Hashjoin %p: increasing nbuckets %d => %d\n",
hashtable, hashtable->nbuckets, hashtable->nbuckets_optimal);
#endif
hashtable->nbuckets = hashtable->nbuckets_optimal;
hashtable->log2_nbuckets = hashtable->log2_nbuckets_optimal;
Assert(hashtable->nbuckets > 1);
Assert(hashtable->nbuckets <= (INT_MAX / 2));
Assert(hashtable->nbuckets == (1 << hashtable->log2_nbuckets));
/*
* Just reallocate the proper number of buckets - we don't need to walk
* through them - we can walk the dense-allocated chunks (just like in
* ExecHashIncreaseNumBatches, but without all the copying into new
* chunks)
*/
hashtable->buckets.unshared =
(HashJoinTuple *) repalloc(hashtable->buckets.unshared,
hashtable->nbuckets * sizeof(HashJoinTuple));
memset(hashtable->buckets.unshared, 0,
hashtable->nbuckets * sizeof(HashJoinTuple));
/* scan through all tuples in all chunks to rebuild the hash table */
for (chunk = hashtable->chunks; chunk != NULL; chunk = chunk->next.unshared)
{
/* process all tuples stored in this chunk */
size_t idx = 0;
while (idx < chunk->used)
{
HashJoinTuple hashTuple = (HashJoinTuple) (HASH_CHUNK_DATA(chunk) + idx);
int bucketno;
int batchno;
ExecHashGetBucketAndBatch(hashtable, hashTuple->hashvalue,
&bucketno, &batchno);
/* add the tuple to the proper bucket */
hashTuple->next.unshared = hashtable->buckets.unshared[bucketno];
hashtable->buckets.unshared[bucketno] = hashTuple;
/* advance index past the tuple */
idx += MAXALIGN(HJTUPLE_OVERHEAD +
HJTUPLE_MINTUPLE(hashTuple)->t_len);
}
/* allow this loop to be cancellable */
CHECK_FOR_INTERRUPTS();
}
}
static void
ExecParallelHashIncreaseNumBuckets(HashJoinTable hashtable)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
int i;
HashMemoryChunk chunk;
dsa_pointer chunk_s;
Assert(BarrierPhase(&pstate->build_barrier) == PHJ_BUILD_HASHING_INNER);
/*
* It's unlikely, but we need to be prepared for new participants to show
* up while we're in the middle of this operation so we need to switch on
* barrier phase here.
*/
switch (PHJ_GROW_BUCKETS_PHASE(BarrierPhase(&pstate->grow_buckets_barrier)))
{
case PHJ_GROW_BUCKETS_ELECTING:
/* Elect one participant to prepare to increase nbuckets. */
if (BarrierArriveAndWait(&pstate->grow_buckets_barrier,
WAIT_EVENT_HASH_GROW_BUCKETS_ELECTING))
{
size_t size;
dsa_pointer_atomic *buckets;
/* Double the size of the bucket array. */
pstate->nbuckets *= 2;
size = pstate->nbuckets * sizeof(dsa_pointer_atomic);
hashtable->batches[0].shared->size += size / 2;
dsa_free(hashtable->area, hashtable->batches[0].shared->buckets);
hashtable->batches[0].shared->buckets =
dsa_allocate(hashtable->area, size);
buckets = (dsa_pointer_atomic *)
dsa_get_address(hashtable->area,
hashtable->batches[0].shared->buckets);
for (i = 0; i < pstate->nbuckets; ++i)
dsa_pointer_atomic_init(&buckets[i], InvalidDsaPointer);
/* Put the chunk list onto the work queue. */
pstate->chunk_work_queue = hashtable->batches[0].shared->chunks;
/* Clear the flag. */
pstate->growth = PHJ_GROWTH_OK;
}
/* Fall through. */
case PHJ_GROW_BUCKETS_ALLOCATING:
/* Wait for the above to complete. */
BarrierArriveAndWait(&pstate->grow_buckets_barrier,
WAIT_EVENT_HASH_GROW_BUCKETS_ALLOCATING);
/* Fall through. */
case PHJ_GROW_BUCKETS_REINSERTING:
/* Reinsert all tuples into the hash table. */
ExecParallelHashEnsureBatchAccessors(hashtable);
ExecParallelHashTableSetCurrentBatch(hashtable, 0);
while ((chunk = ExecParallelHashPopChunkQueue(hashtable, &chunk_s)))
{
size_t idx = 0;
while (idx < chunk->used)
{
HashJoinTuple hashTuple = (HashJoinTuple) (HASH_CHUNK_DATA(chunk) + idx);
dsa_pointer shared = chunk_s + HASH_CHUNK_HEADER_SIZE + idx;
int bucketno;
int batchno;
ExecHashGetBucketAndBatch(hashtable, hashTuple->hashvalue,
&bucketno, &batchno);
Assert(batchno == 0);
/* add the tuple to the proper bucket */
ExecParallelHashPushTuple(&hashtable->buckets.shared[bucketno],
hashTuple, shared);
/* advance index past the tuple */
idx += MAXALIGN(HJTUPLE_OVERHEAD +
HJTUPLE_MINTUPLE(hashTuple)->t_len);
}
/* allow this loop to be cancellable */
CHECK_FOR_INTERRUPTS();
}
BarrierArriveAndWait(&pstate->grow_buckets_barrier,
WAIT_EVENT_HASH_GROW_BUCKETS_REINSERTING);
}
}
/*
* 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)
{
bool shouldFree;
MinimalTuple tuple = ExecFetchSlotMinimalTuple(slot, &shouldFree);
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;
double ntuples = (hashtable->totalTuples - hashtable->skewTuples);
/* Create the HashJoinTuple */
hashTupleSize = HJTUPLE_OVERHEAD + tuple->t_len;
hashTuple = (HashJoinTuple) dense_alloc(hashtable, hashTupleSize);
hashTuple->hashvalue = hashvalue;
memcpy(HJTUPLE_MINTUPLE(hashTuple), tuple, tuple->t_len);
/*
* We always reset the tuple-matched flag on insertion. This is okay
* even when reloading a tuple from a batch file, since the tuple
* could not possibly have been matched to an outer tuple before it
* went into the batch file.
*/
HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(hashTuple));
/* Push it onto the front of the bucket's list */
hashTuple->next.unshared = hashtable->buckets.unshared[bucketno];
hashtable->buckets.unshared[bucketno] = hashTuple;
/*
* Increase the (optimal) number of buckets if we just exceeded the
* NTUP_PER_BUCKET threshold, but only when there's still a single
* batch.
*/
if (hashtable->nbatch == 1 &&
ntuples > (hashtable->nbuckets_optimal * NTUP_PER_BUCKET))
{
/* Guard against integer overflow and alloc size overflow */
if (hashtable->nbuckets_optimal <= INT_MAX / 2 &&
hashtable->nbuckets_optimal * 2 <= MaxAllocSize / sizeof(HashJoinTuple))
{
hashtable->nbuckets_optimal *= 2;
hashtable->log2_nbuckets_optimal += 1;
}
}
/* Account for space used, and back off if we've used too much */
hashtable->spaceUsed += hashTupleSize;
if (hashtable->spaceUsed > hashtable->spacePeak)
hashtable->spacePeak = hashtable->spaceUsed;
if (hashtable->spaceUsed +
hashtable->nbuckets_optimal * sizeof(HashJoinTuple)
> 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]);
}
if (shouldFree)
heap_free_minimal_tuple(tuple);
}
/*
* ExecParallelHashTableInsert
* insert a tuple into a shared hash table or shared batch tuplestore
*/
void
ExecParallelHashTableInsert(HashJoinTable hashtable,
TupleTableSlot *slot,
uint32 hashvalue)
{
bool shouldFree;
MinimalTuple tuple = ExecFetchSlotMinimalTuple(slot, &shouldFree);
dsa_pointer shared;
int bucketno;
int batchno;
retry:
ExecHashGetBucketAndBatch(hashtable, hashvalue, &bucketno, &batchno);
if (batchno == 0)
{
HashJoinTuple hashTuple;
/* Try to load it into memory. */
Assert(BarrierPhase(&hashtable->parallel_state->build_barrier) ==
PHJ_BUILD_HASHING_INNER);
hashTuple = ExecParallelHashTupleAlloc(hashtable,
HJTUPLE_OVERHEAD + tuple->t_len,
&shared);
if (hashTuple == NULL)
goto retry;
/* Store the hash value in the HashJoinTuple header. */
hashTuple->hashvalue = hashvalue;
memcpy(HJTUPLE_MINTUPLE(hashTuple), tuple, tuple->t_len);
/* Push it onto the front of the bucket's list */
ExecParallelHashPushTuple(&hashtable->buckets.shared[bucketno],
hashTuple, shared);
}
else
{
size_t tuple_size = MAXALIGN(HJTUPLE_OVERHEAD + tuple->t_len);
Assert(batchno > 0);
/* Try to preallocate space in the batch if necessary. */
if (hashtable->batches[batchno].preallocated < tuple_size)
{
if (!ExecParallelHashTuplePrealloc(hashtable, batchno, tuple_size))
goto retry;
}
Assert(hashtable->batches[batchno].preallocated >= tuple_size);
hashtable->batches[batchno].preallocated -= tuple_size;
sts_puttuple(hashtable->batches[batchno].inner_tuples, &hashvalue,
tuple);
}
++hashtable->batches[batchno].ntuples;
if (shouldFree)
heap_free_minimal_tuple(tuple);
}
/*
* Insert a tuple into the current hash table. Unlike
* ExecParallelHashTableInsert, this version is not prepared to send the tuple
* to other batches or to run out of memory, and should only be called with
* tuples that belong in the current batch once growth has been disabled.
*/
void
ExecParallelHashTableInsertCurrentBatch(HashJoinTable hashtable,
TupleTableSlot *slot,
uint32 hashvalue)
{
bool shouldFree;
MinimalTuple tuple = ExecFetchSlotMinimalTuple(slot, &shouldFree);
HashJoinTuple hashTuple;
dsa_pointer shared;
int batchno;
int bucketno;
ExecHashGetBucketAndBatch(hashtable, hashvalue, &bucketno, &batchno);
Assert(batchno == hashtable->curbatch);
hashTuple = ExecParallelHashTupleAlloc(hashtable,
HJTUPLE_OVERHEAD + tuple->t_len,
&shared);
hashTuple->hashvalue = hashvalue;
memcpy(HJTUPLE_MINTUPLE(hashTuple), tuple, tuple->t_len);
HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(hashTuple));
ExecParallelHashPushTuple(&hashtable->buckets.shared[bucketno],
hashTuple, shared);
if (shouldFree)
heap_free_minimal_tuple(tuple);
}
/*
* ExecHashGetHashValue
* Compute the hash value for a tuple
*
* The tuple to be tested must be in econtext->ecxt_outertuple (thus Vars in
* the hashkeys expressions need to have OUTER_VAR as varno). If outer_tuple
* is false (meaning it's the HashJoin's inner node, Hash), econtext,
* hashkeys, and slot need to be from Hash, with hashkeys/slot referencing and
* being suitable for tuples from the node below the Hash. Conversely, if
* outer_tuple is true, econtext is from HashJoin, and hashkeys/slot need to
* be appropriate for tuples from HashJoin's outer node.
*
* 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);
/*
* 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(FunctionCall1Coll(&hashfunctions[i], hashtable->collations[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 and log2_nbuckets may change while nbatch == 1 because of dynamic
* bucket count growth. Once we start batching, the value is fixed and does
* not change over the course of the join (making it possible to compute batch
* number the way we do here).
*
* 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.
*
* On success, the inner tuple is stored into hjstate->hj_CurTuple and
* econtext->ecxt_innertuple, using hjstate->hj_HashTupleSlot as the slot
* for the latter.
*/
bool
ExecScanHashBucket(HashJoinState *hjstate,
ExprContext *econtext)
{
ExprState *hjclauses = hjstate->hashclauses;
HashJoinTable hashtable = hjstate->hj_HashTable;
HashJoinTuple hashTuple = hjstate->hj_CurTuple;
uint32 hashvalue = hjstate->hj_CurHashValue;
/*
* hj_CurTuple is the address of the tuple last returned from the current
* bucket, or NULL if it's time to start scanning a new bucket.
*
* If the tuple hashed to a skew bucket then scan the skew bucket
* otherwise scan the standard hashtable bucket.
*/
if (hashTuple != NULL)
hashTuple = hashTuple->next.unshared;
else if (hjstate->hj_CurSkewBucketNo != INVALID_SKEW_BUCKET_NO)
hashTuple = hashtable->skewBucket[hjstate->hj_CurSkewBucketNo]->tuples;
else
hashTuple = hashtable->buckets.unshared[hjstate->hj_CurBucketNo];
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;
if (ExecQualAndReset(hjclauses, econtext))
{
hjstate->hj_CurTuple = hashTuple;
return true;
}
}
hashTuple = hashTuple->next.unshared;
}
/*
* no match
*/
return false;
}
/*
* ExecParallelScanHashBucket
* scan a hash bucket for matches to the current outer tuple
*
* The current outer tuple must be stored in econtext->ecxt_outertuple.
*
* On success, the inner tuple is stored into hjstate->hj_CurTuple and
* econtext->ecxt_innertuple, using hjstate->hj_HashTupleSlot as the slot
* for the latter.
*/
bool
ExecParallelScanHashBucket(HashJoinState *hjstate,
ExprContext *econtext)
{
ExprState *hjclauses = hjstate->hashclauses;
HashJoinTable hashtable = hjstate->hj_HashTable;
HashJoinTuple hashTuple = hjstate->hj_CurTuple;
uint32 hashvalue = hjstate->hj_CurHashValue;
/*
* hj_CurTuple is the address of the tuple last returned from the current
* bucket, or NULL if it's time to start scanning a new bucket.
*/
if (hashTuple != NULL)
hashTuple = ExecParallelHashNextTuple(hashtable, hashTuple);
else
hashTuple = ExecParallelHashFirstTuple(hashtable,
hjstate->hj_CurBucketNo);
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;
if (ExecQualAndReset(hjclauses, econtext))
{
hjstate->hj_CurTuple = hashTuple;
return true;
}
}
hashTuple = ExecParallelHashNextTuple(hashtable, hashTuple);
}
/*
* no match
*/
return false;
}
/*
* ExecPrepHashTableForUnmatched
* set up for a series of ExecScanHashTableForUnmatched calls
*/
void
ExecPrepHashTableForUnmatched(HashJoinState *hjstate)
{
/*----------
* During this scan we use the HashJoinState fields as follows:
*
* hj_CurBucketNo: next regular bucket to scan
* hj_CurSkewBucketNo: next skew bucket (an index into skewBucketNums)
* hj_CurTuple: last tuple returned, or NULL to start next bucket
*----------
*/
hjstate->hj_CurBucketNo = 0;
hjstate->hj_CurSkewBucketNo = 0;
hjstate->hj_CurTuple = NULL;
}
/*
* ExecScanHashTableForUnmatched
* scan the hash table for unmatched inner tuples
*
* On success, the inner tuple is stored into hjstate->hj_CurTuple and
* econtext->ecxt_innertuple, using hjstate->hj_HashTupleSlot as the slot
* for the latter.
*/
bool
ExecScanHashTableForUnmatched(HashJoinState *hjstate, ExprContext *econtext)
{
HashJoinTable hashtable = hjstate->hj_HashTable;
HashJoinTuple hashTuple = hjstate->hj_CurTuple;
for (;;)
{
/*
* hj_CurTuple is the address of the tuple last returned from the
* current bucket, or NULL if it's time to start scanning a new
* bucket.
*/
if (hashTuple != NULL)
hashTuple = hashTuple->next.unshared;
else if (hjstate->hj_CurBucketNo < hashtable->nbuckets)
{
hashTuple = hashtable->buckets.unshared[hjstate->hj_CurBucketNo];
hjstate->hj_CurBucketNo++;
}
else if (hjstate->hj_CurSkewBucketNo < hashtable->nSkewBuckets)
{
int j = hashtable->skewBucketNums[hjstate->hj_CurSkewBucketNo];
hashTuple = hashtable->skewBucket[j]->tuples;
hjstate->hj_CurSkewBucketNo++;
}
else
break; /* finished all buckets */
while (hashTuple != NULL)
{
if (!HeapTupleHeaderHasMatch(HJTUPLE_MINTUPLE(hashTuple)))
{
TupleTableSlot *inntuple;
/* insert hashtable's tuple into exec slot */
inntuple = ExecStoreMinimalTuple(HJTUPLE_MINTUPLE(hashTuple),
hjstate->hj_HashTupleSlot,
false); /* do not pfree */
econtext->ecxt_innertuple = inntuple;
/*
* Reset temp memory each time; although this function doesn't
* do any qual eval, the caller will, so let's keep it
* parallel to ExecScanHashBucket.
*/
ResetExprContext(econtext);
hjstate->hj_CurTuple = hashTuple;
return true;
}
hashTuple = hashTuple->next.unshared;
}
/* allow this loop to be cancellable */
CHECK_FOR_INTERRUPTS();
}
/*
* no more unmatched tuples
*/
return false;
}
/*
* 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.unshared = (HashJoinTuple *)
palloc0(nbuckets * sizeof(HashJoinTuple));
hashtable->spaceUsed = 0;
MemoryContextSwitchTo(oldcxt);
/* Forget the chunks (the memory was freed by the context reset above). */
hashtable->chunks = NULL;
}
/*
* ExecHashTableResetMatchFlags
* Clear all the HeapTupleHeaderHasMatch flags in the table
*/
void
ExecHashTableResetMatchFlags(HashJoinTable hashtable)
{
HashJoinTuple tuple;
int i;
/* Reset all flags in the main table ... */
for (i = 0; i < hashtable->nbuckets; i++)
{
for (tuple = hashtable->buckets.unshared[i]; tuple != NULL;
tuple = tuple->next.unshared)
HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(tuple));
}
/* ... and the same for the skew buckets, if any */
for (i = 0; i < hashtable->nSkewBuckets; i++)
{
int j = hashtable->skewBucketNums[i];
HashSkewBucket *skewBucket = hashtable->skewBucket[j];
for (tuple = skewBucket->tuples; tuple != NULL; tuple = tuple->next.unshared)
HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(tuple));
}
}
void
ExecReScanHash(HashState *node)
{
/*
* if chgParam of subnode is not null then plan will be re-scanned by
* first ExecProcNode.
*/
if (node->ps.lefttree->chgParam == NULL)
ExecReScan(node->ps.lefttree);
}
/*
* ExecHashBuildSkewHash
*
* Set up for skew optimization if we can identify the most common values
* (MCVs) of the outer relation's join key. We make a skew hash bucket
* for the hash value of each MCV, up to the number of slots allowed
* based on available memory.
*/
static void
ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node, int mcvsToUse)
{
HeapTupleData *statsTuple;
AttStatsSlot sslot;
/* Do nothing if planner didn't identify the outer relation's join key */
if (!OidIsValid(node->skewTable))
return;
/* Also, do nothing if we don't have room for at least one skew bucket */
if (mcvsToUse <= 0)
return;
/*
* Try to find the MCV statistics for the outer relation's join key.
*/
statsTuple = SearchSysCache3(STATRELATTINH,
ObjectIdGetDatum(node->skewTable),
Int16GetDatum(node->skewColumn),
BoolGetDatum(node->skewInherit));
if (!HeapTupleIsValid(statsTuple))
return;
if (get_attstatsslot(&sslot, statsTuple,
STATISTIC_KIND_MCV, InvalidOid,
ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS))
{
double frac;
int nbuckets;
FmgrInfo *hashfunctions;
int i;
if (mcvsToUse > sslot.nvalues)
mcvsToUse = sslot.nvalues;
/*
* Calculate the expected fraction of outer relation that will
* participate in the skew optimization. If this isn't at least
* SKEW_MIN_OUTER_FRACTION, don't use skew optimization.
*/
frac = 0;
for (i = 0; i < mcvsToUse; i++)
frac += sslot.numbers[i];
if (frac < SKEW_MIN_OUTER_FRACTION)
{
free_attstatsslot(&sslot);
ReleaseSysCache(statsTuple);
return;
}
/*
* Okay, set up the skew hashtable.
*
* skewBucket[] is an open addressing hashtable with a power of 2 size
* that is greater than the number of MCV values. (This ensures there
* will be at least one null entry, so searches will always
* terminate.)
*
* Note: this code could fail if mcvsToUse exceeds INT_MAX/8 or
* MaxAllocSize/sizeof(void *)/8, but that is not currently possible
* since we limit pg_statistic entries to much less than that.
*/
nbuckets = 2;
while (nbuckets <= mcvsToUse)
nbuckets <<= 1;
/* use two more bits just to help avoid collisions */
nbuckets <<= 2;
hashtable->skewEnabled = true;
hashtable->skewBucketLen = nbuckets;
/*
* We allocate the bucket memory in the hashtable's batch context. It
* is only needed during the first batch, and this ensures it will be
* automatically removed once the first batch is done.
*/
hashtable->skewBucket = (HashSkewBucket **)
MemoryContextAllocZero(hashtable->batchCxt,
nbuckets * sizeof(HashSkewBucket *));
hashtable->skewBucketNums = (int *)
MemoryContextAllocZero(hashtable->batchCxt,
mcvsToUse * sizeof(int));
hashtable->spaceUsed += nbuckets * sizeof(HashSkewBucket *)
+ mcvsToUse * sizeof(int);
hashtable->spaceUsedSkew += nbuckets * sizeof(HashSkewBucket *)
+ mcvsToUse * sizeof(int);
if (hashtable->spaceUsed > hashtable->spacePeak)
hashtable->spacePeak = hashtable->spaceUsed;
/*
* Create a skew bucket for each MCV hash value.
*
* Note: it is very important that we create the buckets in order of
* decreasing MCV frequency. If we have to remove some buckets, they
* must be removed in reverse order of creation (see notes in
* ExecHashRemoveNextSkewBucket) and we want the least common MCVs to
* be removed first.
*/
hashfunctions = hashtable->outer_hashfunctions;
for (i = 0; i < mcvsToUse; i++)
{
uint32 hashvalue;
int bucket;
hashvalue = DatumGetUInt32(FunctionCall1Coll(&hashfunctions[0],
hashtable->collations[0],
sslot.values[i]));
/*
* While we have not hit a hole in the hashtable and have not hit
* the desired bucket, we have collided with some previous hash
* value, so try the next bucket location. NB: this code must
* match ExecHashGetSkewBucket.
*/
bucket = hashvalue & (nbuckets - 1);
while (hashtable->skewBucket[bucket] != NULL &&
hashtable->skewBucket[bucket]->hashvalue != hashvalue)
bucket = (bucket + 1) & (nbuckets - 1);
/*
* If we found an existing bucket with the same hashvalue, leave
* it alone. It's okay for two MCVs to share a hashvalue.
*/
if (hashtable->skewBucket[bucket] != NULL)
continue;
/* Okay, create a new skew bucket for this hashvalue. */
hashtable->skewBucket[bucket] = (HashSkewBucket *)
MemoryContextAlloc(hashtable->batchCxt,
sizeof(HashSkewBucket));
hashtable->skewBucket[bucket]->hashvalue = hashvalue;
hashtable->skewBucket[bucket]->tuples = NULL;
hashtable->skewBucketNums[hashtable->nSkewBuckets] = bucket;
hashtable->nSkewBuckets++;
hashtable->spaceUsed += SKEW_BUCKET_OVERHEAD;
hashtable->spaceUsedSkew += SKEW_BUCKET_OVERHEAD;
if (hashtable->spaceUsed > hashtable->spacePeak)
hashtable->spacePeak = hashtable->spaceUsed;
}
free_attstatsslot(&sslot);
}
ReleaseSysCache(statsTuple);
}
/*
* ExecHashGetSkewBucket
*
* Returns the index of the skew bucket for this hashvalue,
* or INVALID_SKEW_BUCKET_NO if the hashvalue is not
* associated with any active skew bucket.
*/
int
ExecHashGetSkewBucket(HashJoinTable hashtable, uint32 hashvalue)
{
int bucket;
/*
* Always return INVALID_SKEW_BUCKET_NO if not doing skew optimization (in
* particular, this happens after the initial batch is done).
*/
if (!hashtable->skewEnabled)
return INVALID_SKEW_BUCKET_NO;
/*
* Since skewBucketLen is a power of 2, we can do a modulo by ANDing.
*/
bucket = hashvalue & (hashtable->skewBucketLen - 1);
/*
* While we have not hit a hole in the hashtable and have not hit the
* desired bucket, we have collided with some other hash value, so try the
* next bucket location.
*/
while (hashtable->skewBucket[bucket] != NULL &&
hashtable->skewBucket[bucket]->hashvalue != hashvalue)
bucket = (bucket + 1) & (hashtable->skewBucketLen - 1);
/*
* Found the desired bucket?
*/
if (hashtable->skewBucket[bucket] != NULL)
return bucket;
/*
* There must not be any hashtable entry for this hash value.
*/
return INVALID_SKEW_BUCKET_NO;
}
/*
* ExecHashSkewTableInsert
*
* Insert a tuple into the skew hashtable.
*
* This should generally match up with the current-batch case in
* ExecHashTableInsert.
*/
static void
ExecHashSkewTableInsert(HashJoinTable hashtable,
TupleTableSlot *slot,
uint32 hashvalue,
int bucketNumber)
{
bool shouldFree;
MinimalTuple tuple = ExecFetchSlotMinimalTuple(slot, &shouldFree);
HashJoinTuple hashTuple;
int hashTupleSize;
/* Create the HashJoinTuple */
hashTupleSize = HJTUPLE_OVERHEAD + tuple->t_len;
hashTuple = (HashJoinTuple) MemoryContextAlloc(hashtable->batchCxt,
hashTupleSize);
hashTuple->hashvalue = hashvalue;
memcpy(HJTUPLE_MINTUPLE(hashTuple), tuple, tuple->t_len);
HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(hashTuple));
/* Push it onto the front of the skew bucket's list */
hashTuple->next.unshared = hashtable->skewBucket[bucketNumber]->tuples;
hashtable->skewBucket[bucketNumber]->tuples = hashTuple;
Assert(hashTuple != hashTuple->next.unshared);
/* Account for space used, and back off if we've used too much */
hashtable->spaceUsed += hashTupleSize;
hashtable->spaceUsedSkew += hashTupleSize;
if (hashtable->spaceUsed > hashtable->spacePeak)
hashtable->spacePeak = hashtable->spaceUsed;
while (hashtable->spaceUsedSkew > hashtable->spaceAllowedSkew)
ExecHashRemoveNextSkewBucket(hashtable);
/* Check we are not over the total spaceAllowed, either */
if (hashtable->spaceUsed > hashtable->spaceAllowed)
ExecHashIncreaseNumBatches(hashtable);
if (shouldFree)
heap_free_minimal_tuple(tuple);
}
/*
* ExecHashRemoveNextSkewBucket
*
* Remove the least valuable skew bucket by pushing its tuples into
* the main hash table.
*/
static void
ExecHashRemoveNextSkewBucket(HashJoinTable hashtable)
{
int bucketToRemove;
HashSkewBucket *bucket;
uint32 hashvalue;
int bucketno;
int batchno;
HashJoinTuple hashTuple;
/* Locate the bucket to remove */
bucketToRemove = hashtable->skewBucketNums[hashtable->nSkewBuckets - 1];
bucket = hashtable->skewBucket[bucketToRemove];
/*
* Calculate which bucket and batch the tuples belong to in the main
* hashtable. They all have the same hash value, so it's the same for all
* of them. Also note that it's not possible for nbatch to increase while
* we are processing the tuples.
*/
hashvalue = bucket->hashvalue;
ExecHashGetBucketAndBatch(hashtable, hashvalue, &bucketno, &batchno);
/* Process all tuples in the bucket */
hashTuple = bucket->tuples;
while (hashTuple != NULL)
{
HashJoinTuple nextHashTuple = hashTuple->next.unshared;
MinimalTuple tuple;
Size tupleSize;
/*
* This code must agree with ExecHashTableInsert. We do not use
* ExecHashTableInsert directly as ExecHashTableInsert expects a
* TupleTableSlot while we already have HashJoinTuples.
*/
tuple = HJTUPLE_MINTUPLE(hashTuple);
tupleSize = HJTUPLE_OVERHEAD + tuple->t_len;
/* Decide whether to put the tuple in the hash table or a temp file */
if (batchno == hashtable->curbatch)
{
/* Move the tuple to the main hash table */
HashJoinTuple copyTuple;
/*
* We must copy the tuple into the dense storage, else it will not
* be found by, eg, ExecHashIncreaseNumBatches.
*/
copyTuple = (HashJoinTuple) dense_alloc(hashtable, tupleSize);
memcpy(copyTuple, hashTuple, tupleSize);
pfree(hashTuple);
copyTuple->next.unshared = hashtable->buckets.unshared[bucketno];
hashtable->buckets.unshared[bucketno] = copyTuple;
/* We have reduced skew space, but overall space doesn't change */
hashtable->spaceUsedSkew -= tupleSize;
}
else
{
/* Put the tuple into a temp file for later batches */
Assert(batchno > hashtable->curbatch);
ExecHashJoinSaveTuple(tuple, hashvalue,
&hashtable->innerBatchFile[batchno]);
pfree(hashTuple);
hashtable->spaceUsed -= tupleSize;
hashtable->spaceUsedSkew -= tupleSize;
}
hashTuple = nextHashTuple;
/* allow this loop to be cancellable */
CHECK_FOR_INTERRUPTS();
}
/*
* Free the bucket struct itself and reset the hashtable entry to NULL.
*
* NOTE: this is not nearly as simple as it looks on the surface, because
* of the possibility of collisions in the hashtable. Suppose that hash
* values A and B collide at a particular hashtable entry, and that A was
* entered first so B gets shifted to a different table entry. If we were
* to remove A first then ExecHashGetSkewBucket would mistakenly start
* reporting that B is not in the hashtable, because it would hit the NULL
* before finding B. However, we always remove entries in the reverse
* order of creation, so this failure cannot happen.
*/
hashtable->skewBucket[bucketToRemove] = NULL;
hashtable->nSkewBuckets--;
pfree(bucket);
hashtable->spaceUsed -= SKEW_BUCKET_OVERHEAD;
hashtable->spaceUsedSkew -= SKEW_BUCKET_OVERHEAD;
/*
* If we have removed all skew buckets then give up on skew optimization.
* Release the arrays since they aren't useful any more.
*/
if (hashtable->nSkewBuckets == 0)
{
hashtable->skewEnabled = false;
pfree(hashtable->skewBucket);
pfree(hashtable->skewBucketNums);
hashtable->skewBucket = NULL;
hashtable->skewBucketNums = NULL;
hashtable->spaceUsed -= hashtable->spaceUsedSkew;
hashtable->spaceUsedSkew = 0;
}
}
/*
* Reserve space in the DSM segment for instrumentation data.
*/
void
ExecHashEstimate(HashState *node, ParallelContext *pcxt)
{
size_t size;
/* don't need this if not instrumenting or no workers */
if (!node->ps.instrument || pcxt->nworkers == 0)
return;
size = mul_size(pcxt->nworkers, sizeof(HashInstrumentation));
size = add_size(size, offsetof(SharedHashInfo, hinstrument));
shm_toc_estimate_chunk(&pcxt->estimator, size);
shm_toc_estimate_keys(&pcxt->estimator, 1);
}
/*
* Set up a space in the DSM for all workers to record instrumentation data
* about their hash table.
*/
void
ExecHashInitializeDSM(HashState *node, ParallelContext *pcxt)
{
size_t size;
/* don't need this if not instrumenting or no workers */
if (!node->ps.instrument || pcxt->nworkers == 0)
return;
size = offsetof(SharedHashInfo, hinstrument) +
pcxt->nworkers * sizeof(HashInstrumentation);
node->shared_info = (SharedHashInfo *) shm_toc_allocate(pcxt->toc, size);
memset(node->shared_info, 0, size);
node->shared_info->num_workers = pcxt->nworkers;
shm_toc_insert(pcxt->toc, node->ps.plan->plan_node_id,
node->shared_info);
}
/*
* Locate the DSM space for hash table instrumentation data that we'll write
* to at shutdown time.
*/
void
ExecHashInitializeWorker(HashState *node, ParallelWorkerContext *pwcxt)
{
SharedHashInfo *shared_info;
/* don't need this if not instrumenting */
if (!node->ps.instrument)
return;
shared_info = (SharedHashInfo *)
shm_toc_lookup(pwcxt->toc, node->ps.plan->plan_node_id, false);
node->hinstrument = &shared_info->hinstrument[ParallelWorkerNumber];
}
/*
* Copy instrumentation data from this worker's hash table (if it built one)
* to DSM memory so the leader can retrieve it. This must be done in an
* ExecShutdownHash() rather than ExecEndHash() because the latter runs after
* we've detached from the DSM segment.
*/
void
ExecShutdownHash(HashState *node)
{
if (node->hinstrument && node->hashtable)
ExecHashGetInstrumentation(node->hinstrument, node->hashtable);
}
/*
* Retrieve instrumentation data from workers before the DSM segment is
* detached, so that EXPLAIN can access it.
*/
void
ExecHashRetrieveInstrumentation(HashState *node)
{
SharedHashInfo *shared_info = node->shared_info;
size_t size;
if (shared_info == NULL)
return;
/* Replace node->shared_info with a copy in backend-local memory. */
size = offsetof(SharedHashInfo, hinstrument) +
shared_info->num_workers * sizeof(HashInstrumentation);
node->shared_info = palloc(size);
memcpy(node->shared_info, shared_info, size);
}
/*
* Copy the instrumentation data from 'hashtable' into a HashInstrumentation
* struct.
*/
void
ExecHashGetInstrumentation(HashInstrumentation *instrument,
HashJoinTable hashtable)
{
instrument->nbuckets = hashtable->nbuckets;
instrument->nbuckets_original = hashtable->nbuckets_original;
instrument->nbatch = hashtable->nbatch;
instrument->nbatch_original = hashtable->nbatch_original;
instrument->space_peak = hashtable->spacePeak;
}
/*
* Allocate 'size' bytes from the currently active HashMemoryChunk
*/
static void *
dense_alloc(HashJoinTable hashtable, Size size)
{
HashMemoryChunk newChunk;
char *ptr;
/* just in case the size is not already aligned properly */
size = MAXALIGN(size);
/*
* If tuple size is larger than threshold, allocate a separate chunk.
*/
if (size > HASH_CHUNK_THRESHOLD)
{
/* allocate new chunk and put it at the beginning of the list */
newChunk = (HashMemoryChunk) MemoryContextAlloc(hashtable->batchCxt,
HASH_CHUNK_HEADER_SIZE + size);
newChunk->maxlen = size;
newChunk->used = size;
newChunk->ntuples = 1;
/*
* Add this chunk to the list after the first existing chunk, so that
* we don't lose the remaining space in the "current" chunk.
*/
if (hashtable->chunks != NULL)
{
newChunk->next = hashtable->chunks->next;
hashtable->chunks->next.unshared = newChunk;
}
else
{
newChunk->next.unshared = hashtable->chunks;
hashtable->chunks = newChunk;
}
return HASH_CHUNK_DATA(newChunk);
}
/*
* See if we have enough space for it in the current chunk (if any). If
* not, allocate a fresh chunk.
*/
if ((hashtable->chunks == NULL) ||
(hashtable->chunks->maxlen - hashtable->chunks->used) < size)
{
/* allocate new chunk and put it at the beginning of the list */
newChunk = (HashMemoryChunk) MemoryContextAlloc(hashtable->batchCxt,
HASH_CHUNK_HEADER_SIZE + HASH_CHUNK_SIZE);
newChunk->maxlen = HASH_CHUNK_SIZE;
newChunk->used = size;
newChunk->ntuples = 1;
newChunk->next.unshared = hashtable->chunks;
hashtable->chunks = newChunk;
return HASH_CHUNK_DATA(newChunk);
}
/* There is enough space in the current chunk, let's add the tuple */
ptr = HASH_CHUNK_DATA(hashtable->chunks) + hashtable->chunks->used;
hashtable->chunks->used += size;
hashtable->chunks->ntuples += 1;
/* return pointer to the start of the tuple memory */
return ptr;
}
/*
* Allocate space for a tuple in shared dense storage. This is equivalent to
* dense_alloc but for Parallel Hash using shared memory.
*
* While loading a tuple into shared memory, we might run out of memory and
* decide to repartition, or determine that the load factor is too high and
* decide to expand the bucket array, or discover that another participant has
* commanded us to help do that. Return NULL if number of buckets or batches
* has changed, indicating that the caller must retry (considering the
* possibility that the tuple no longer belongs in the same batch).
*/
static HashJoinTuple
ExecParallelHashTupleAlloc(HashJoinTable hashtable, size_t size,
dsa_pointer *shared)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
dsa_pointer chunk_shared;
HashMemoryChunk chunk;
Size chunk_size;
HashJoinTuple result;
int curbatch = hashtable->curbatch;
size = MAXALIGN(size);
/*
* Fast path: if there is enough space in this backend's current chunk,
* then we can allocate without any locking.
*/
chunk = hashtable->current_chunk;
if (chunk != NULL &&
size <= HASH_CHUNK_THRESHOLD &&
chunk->maxlen - chunk->used >= size)
{
chunk_shared = hashtable->current_chunk_shared;
Assert(chunk == dsa_get_address(hashtable->area, chunk_shared));
*shared = chunk_shared + HASH_CHUNK_HEADER_SIZE + chunk->used;
result = (HashJoinTuple) (HASH_CHUNK_DATA(chunk) + chunk->used);
chunk->used += size;
Assert(chunk->used <= chunk->maxlen);
Assert(result == dsa_get_address(hashtable->area, *shared));
return result;
}
/* Slow path: try to allocate a new chunk. */
LWLockAcquire(&pstate->lock, LW_EXCLUSIVE);
/*
* Check if we need to help increase the number of buckets or batches.
*/
if (pstate->growth == PHJ_GROWTH_NEED_MORE_BATCHES ||
pstate->growth == PHJ_GROWTH_NEED_MORE_BUCKETS)
{
ParallelHashGrowth growth = pstate->growth;
hashtable->current_chunk = NULL;
LWLockRelease(&pstate->lock);
/* Another participant has commanded us to help grow. */
if (growth == PHJ_GROWTH_NEED_MORE_BATCHES)
ExecParallelHashIncreaseNumBatches(hashtable);
else if (growth == PHJ_GROWTH_NEED_MORE_BUCKETS)
ExecParallelHashIncreaseNumBuckets(hashtable);
/* The caller must retry. */
return NULL;
}
/* Oversized tuples get their own chunk. */
if (size > HASH_CHUNK_THRESHOLD)
chunk_size = size + HASH_CHUNK_HEADER_SIZE;
else
chunk_size = HASH_CHUNK_SIZE;
/* Check if it's time to grow batches or buckets. */
if (pstate->growth != PHJ_GROWTH_DISABLED)
{
Assert(curbatch == 0);
Assert(BarrierPhase(&pstate->build_barrier) == PHJ_BUILD_HASHING_INNER);
/*
* Check if our space limit would be exceeded. To avoid choking on
* very large tuples or very low work_mem setting, we'll always allow
* each backend to allocate at least one chunk.
*/
if (hashtable->batches[0].at_least_one_chunk &&
hashtable->batches[0].shared->size +
chunk_size > pstate->space_allowed)
{
pstate->growth = PHJ_GROWTH_NEED_MORE_BATCHES;
hashtable->batches[0].shared->space_exhausted = true;
LWLockRelease(&pstate->lock);
return NULL;
}
/* Check if our load factor limit would be exceeded. */
if (hashtable->nbatch == 1)
{
hashtable->batches[0].shared->ntuples += hashtable->batches[0].ntuples;
hashtable->batches[0].ntuples = 0;
/* Guard against integer overflow and alloc size overflow */
if (hashtable->batches[0].shared->ntuples + 1 >
hashtable->nbuckets * NTUP_PER_BUCKET &&
hashtable->nbuckets < (INT_MAX / 2) &&
hashtable->nbuckets * 2 <=
MaxAllocSize / sizeof(dsa_pointer_atomic))
{
pstate->growth = PHJ_GROWTH_NEED_MORE_BUCKETS;
LWLockRelease(&pstate->lock);
return NULL;
}
}
}
/* We are cleared to allocate a new chunk. */
chunk_shared = dsa_allocate(hashtable->area, chunk_size);
hashtable->batches[curbatch].shared->size += chunk_size;
hashtable->batches[curbatch].at_least_one_chunk = true;
/* Set up the chunk. */
chunk = (HashMemoryChunk) dsa_get_address(hashtable->area, chunk_shared);
*shared = chunk_shared + HASH_CHUNK_HEADER_SIZE;
chunk->maxlen = chunk_size - HASH_CHUNK_HEADER_SIZE;
chunk->used = size;
/*
* Push it onto the list of chunks, so that it can be found if we need to
* increase the number of buckets or batches (batch 0 only) and later for
* freeing the memory (all batches).
*/
chunk->next.shared = hashtable->batches[curbatch].shared->chunks;
hashtable->batches[curbatch].shared->chunks = chunk_shared;
if (size <= HASH_CHUNK_THRESHOLD)
{
/*
* Make this the current chunk so that we can use the fast path to
* fill the rest of it up in future calls.
*/
hashtable->current_chunk = chunk;
hashtable->current_chunk_shared = chunk_shared;
}
LWLockRelease(&pstate->lock);
Assert(HASH_CHUNK_DATA(chunk) == dsa_get_address(hashtable->area, *shared));
result = (HashJoinTuple) HASH_CHUNK_DATA(chunk);
return result;
}
/*
* One backend needs to set up the shared batch state including tuplestores.
* Other backends will ensure they have correctly configured accessors by
* called ExecParallelHashEnsureBatchAccessors().
*/
static void
ExecParallelHashJoinSetUpBatches(HashJoinTable hashtable, int nbatch)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
ParallelHashJoinBatch *batches;
MemoryContext oldcxt;
int i;
Assert(hashtable->batches == NULL);
/* Allocate space. */
pstate->batches =
dsa_allocate0(hashtable->area,
EstimateParallelHashJoinBatch(hashtable) * nbatch);
pstate->nbatch = nbatch;
batches = dsa_get_address(hashtable->area, pstate->batches);
/* Use hash join memory context. */
oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);
/* Allocate this backend's accessor array. */
hashtable->nbatch = nbatch;
hashtable->batches = (ParallelHashJoinBatchAccessor *)
palloc0(sizeof(ParallelHashJoinBatchAccessor) * hashtable->nbatch);
/* Set up the shared state, tuplestores and backend-local accessors. */
for (i = 0; i < hashtable->nbatch; ++i)
{
ParallelHashJoinBatchAccessor *accessor = &hashtable->batches[i];
ParallelHashJoinBatch *shared = NthParallelHashJoinBatch(batches, i);
char name[MAXPGPATH];
/*
* All members of shared were zero-initialized. We just need to set
* up the Barrier.
*/
BarrierInit(&shared->batch_barrier, 0);
if (i == 0)
{
/* Batch 0 doesn't need to be loaded. */
BarrierAttach(&shared->batch_barrier);
while (BarrierPhase(&shared->batch_barrier) < PHJ_BATCH_PROBING)
BarrierArriveAndWait(&shared->batch_barrier, 0);
BarrierDetach(&shared->batch_barrier);
}
/* Initialize accessor state. All members were zero-initialized. */
accessor->shared = shared;
/* Initialize the shared tuplestores. */
snprintf(name, sizeof(name), "i%dof%d", i, hashtable->nbatch);
accessor->inner_tuples =
sts_initialize(ParallelHashJoinBatchInner(shared),
pstate->nparticipants,
ParallelWorkerNumber + 1,
sizeof(uint32),
SHARED_TUPLESTORE_SINGLE_PASS,
&pstate->fileset,
name);
snprintf(name, sizeof(name), "o%dof%d", i, hashtable->nbatch);
accessor->outer_tuples =
sts_initialize(ParallelHashJoinBatchOuter(shared,
pstate->nparticipants),
pstate->nparticipants,
ParallelWorkerNumber + 1,
sizeof(uint32),
SHARED_TUPLESTORE_SINGLE_PASS,
&pstate->fileset,
name);
}
MemoryContextSwitchTo(oldcxt);
}
/*
* Free the current set of ParallelHashJoinBatchAccessor objects.
*/
static void
ExecParallelHashCloseBatchAccessors(HashJoinTable hashtable)
{
int i;
for (i = 0; i < hashtable->nbatch; ++i)
{
/* Make sure no files are left open. */
sts_end_write(hashtable->batches[i].inner_tuples);
sts_end_write(hashtable->batches[i].outer_tuples);
sts_end_parallel_scan(hashtable->batches[i].inner_tuples);
sts_end_parallel_scan(hashtable->batches[i].outer_tuples);
}
pfree(hashtable->batches);
hashtable->batches = NULL;
}
/*
* Make sure this backend has up-to-date accessors for the current set of
* batches.
*/
static void
ExecParallelHashEnsureBatchAccessors(HashJoinTable hashtable)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
ParallelHashJoinBatch *batches;
MemoryContext oldcxt;
int i;
if (hashtable->batches != NULL)
{
if (hashtable->nbatch == pstate->nbatch)
return;
ExecParallelHashCloseBatchAccessors(hashtable);
}
/*
* It's possible for a backend to start up very late so that the whole
* join is finished and the shm state for tracking batches has already
* been freed by ExecHashTableDetach(). In that case we'll just leave
* hashtable->batches as NULL so that ExecParallelHashJoinNewBatch() gives
* up early.
*/
if (!DsaPointerIsValid(pstate->batches))
return;
/* Use hash join memory context. */
oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);
/* Allocate this backend's accessor array. */
hashtable->nbatch = pstate->nbatch;
hashtable->batches = (ParallelHashJoinBatchAccessor *)
palloc0(sizeof(ParallelHashJoinBatchAccessor) * hashtable->nbatch);
/* Find the base of the pseudo-array of ParallelHashJoinBatch objects. */
batches = (ParallelHashJoinBatch *)
dsa_get_address(hashtable->area, pstate->batches);
/* Set up the accessor array and attach to the tuplestores. */
for (i = 0; i < hashtable->nbatch; ++i)
{
ParallelHashJoinBatchAccessor *accessor = &hashtable->batches[i];
ParallelHashJoinBatch *shared = NthParallelHashJoinBatch(batches, i);
accessor->shared = shared;
accessor->preallocated = 0;
accessor->done = false;
accessor->inner_tuples =
sts_attach(ParallelHashJoinBatchInner(shared),
ParallelWorkerNumber + 1,
&pstate->fileset);
accessor->outer_tuples =
sts_attach(ParallelHashJoinBatchOuter(shared,
pstate->nparticipants),
ParallelWorkerNumber + 1,
&pstate->fileset);
}
MemoryContextSwitchTo(oldcxt);
}
/*
* Allocate an empty shared memory hash table for a given batch.
*/
void
ExecParallelHashTableAlloc(HashJoinTable hashtable, int batchno)
{
ParallelHashJoinBatch *batch = hashtable->batches[batchno].shared;
dsa_pointer_atomic *buckets;
int nbuckets = hashtable->parallel_state->nbuckets;
int i;
batch->buckets =
dsa_allocate(hashtable->area, sizeof(dsa_pointer_atomic) * nbuckets);
buckets = (dsa_pointer_atomic *)
dsa_get_address(hashtable->area, batch->buckets);
for (i = 0; i < nbuckets; ++i)
dsa_pointer_atomic_init(&buckets[i], InvalidDsaPointer);
}
/*
* If we are currently attached to a shared hash join batch, detach. If we
* are last to detach, clean up.
*/
void
ExecHashTableDetachBatch(HashJoinTable hashtable)
{
if (hashtable->parallel_state != NULL &&
hashtable->curbatch >= 0)
{
int curbatch = hashtable->curbatch;
ParallelHashJoinBatch *batch = hashtable->batches[curbatch].shared;
/* Make sure any temporary files are closed. */
sts_end_parallel_scan(hashtable->batches[curbatch].inner_tuples);
sts_end_parallel_scan(hashtable->batches[curbatch].outer_tuples);
/* Detach from the batch we were last working on. */
if (BarrierArriveAndDetach(&batch->batch_barrier))
{
/*
* Technically we shouldn't access the barrier because we're no
* longer attached, but since there is no way it's moving after
* this point it seems safe to make the following assertion.
*/
Assert(BarrierPhase(&batch->batch_barrier) == PHJ_BATCH_DONE);
/* Free shared chunks and buckets. */
while (DsaPointerIsValid(batch->chunks))
{
HashMemoryChunk chunk =
dsa_get_address(hashtable->area, batch->chunks);
dsa_pointer next = chunk->next.shared;
dsa_free(hashtable->area, batch->chunks);
batch->chunks = next;
}
if (DsaPointerIsValid(batch->buckets))
{
dsa_free(hashtable->area, batch->buckets);
batch->buckets = InvalidDsaPointer;
}
}
/*
* Track the largest batch we've been attached to. Though each
* backend might see a different subset of batches, explain.c will
* scan the results from all backends to find the largest value.
*/
hashtable->spacePeak =
Max(hashtable->spacePeak,
batch->size + sizeof(dsa_pointer_atomic) * hashtable->nbuckets);
/* Remember that we are not attached to a batch. */
hashtable->curbatch = -1;
}
}
/*
* Detach from all shared resources. If we are last to detach, clean up.
*/
void
ExecHashTableDetach(HashJoinTable hashtable)
{
if (hashtable->parallel_state)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
int i;
/* Make sure any temporary files are closed. */
if (hashtable->batches)
{
for (i = 0; i < hashtable->nbatch; ++i)
{
sts_end_write(hashtable->batches[i].inner_tuples);
sts_end_write(hashtable->batches[i].outer_tuples);
sts_end_parallel_scan(hashtable->batches[i].inner_tuples);
sts_end_parallel_scan(hashtable->batches[i].outer_tuples);
}
}
/* If we're last to detach, clean up shared memory. */
if (BarrierDetach(&pstate->build_barrier))
{
if (DsaPointerIsValid(pstate->batches))
{
dsa_free(hashtable->area, pstate->batches);
pstate->batches = InvalidDsaPointer;
}
}
hashtable->parallel_state = NULL;
}
}
/*
* Get the first tuple in a given bucket identified by number.
*/
static inline HashJoinTuple
ExecParallelHashFirstTuple(HashJoinTable hashtable, int bucketno)
{
HashJoinTuple tuple;
dsa_pointer p;
Assert(hashtable->parallel_state);
p = dsa_pointer_atomic_read(&hashtable->buckets.shared[bucketno]);
tuple = (HashJoinTuple) dsa_get_address(hashtable->area, p);
return tuple;
}
/*
* Get the next tuple in the same bucket as 'tuple'.
*/
static inline HashJoinTuple
ExecParallelHashNextTuple(HashJoinTable hashtable, HashJoinTuple tuple)
{
HashJoinTuple next;
Assert(hashtable->parallel_state);
next = (HashJoinTuple) dsa_get_address(hashtable->area, tuple->next.shared);
return next;
}
/*
* Insert a tuple at the front of a chain of tuples in DSA memory atomically.
*/
static inline void
ExecParallelHashPushTuple(dsa_pointer_atomic *head,
HashJoinTuple tuple,
dsa_pointer tuple_shared)
{
for (;;)
{
tuple->next.shared = dsa_pointer_atomic_read(head);
if (dsa_pointer_atomic_compare_exchange(head,
&tuple->next.shared,
tuple_shared))
break;
}
}
/*
* Prepare to work on a given batch.
*/
void
ExecParallelHashTableSetCurrentBatch(HashJoinTable hashtable, int batchno)
{
Assert(hashtable->batches[batchno].shared->buckets != InvalidDsaPointer);
hashtable->curbatch = batchno;
hashtable->buckets.shared = (dsa_pointer_atomic *)
dsa_get_address(hashtable->area,
hashtable->batches[batchno].shared->buckets);
hashtable->nbuckets = hashtable->parallel_state->nbuckets;
hashtable->log2_nbuckets = my_log2(hashtable->nbuckets);
hashtable->current_chunk = NULL;
hashtable->current_chunk_shared = InvalidDsaPointer;
hashtable->batches[batchno].at_least_one_chunk = false;
}
/*
* Take the next available chunk from the queue of chunks being worked on in
* parallel. Return NULL if there are none left. Otherwise return a pointer
* to the chunk, and set *shared to the DSA pointer to the chunk.
*/
static HashMemoryChunk
ExecParallelHashPopChunkQueue(HashJoinTable hashtable, dsa_pointer *shared)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
HashMemoryChunk chunk;
LWLockAcquire(&pstate->lock, LW_EXCLUSIVE);
if (DsaPointerIsValid(pstate->chunk_work_queue))
{
*shared = pstate->chunk_work_queue;
chunk = (HashMemoryChunk)
dsa_get_address(hashtable->area, *shared);
pstate->chunk_work_queue = chunk->next.shared;
}
else
chunk = NULL;
LWLockRelease(&pstate->lock);
return chunk;
}
/*
* Increase the space preallocated in this backend for a given inner batch by
* at least a given amount. This allows us to track whether a given batch
* would fit in memory when loaded back in. Also increase the number of
* batches or buckets if required.
*
* This maintains a running estimation of how much space will be taken when we
* load the batch back into memory by simulating the way chunks will be handed
* out to workers. It's not perfectly accurate because the tuples will be
* packed into memory chunks differently by ExecParallelHashTupleAlloc(), but
* it should be pretty close. It tends to overestimate by a fraction of a
* chunk per worker since all workers gang up to preallocate during hashing,
* but workers tend to reload batches alone if there are enough to go around,
* leaving fewer partially filled chunks. This effect is bounded by
* nparticipants.
*
* Return false if the number of batches or buckets has changed, and the
* caller should reconsider which batch a given tuple now belongs in and call
* again.
*/
static bool
ExecParallelHashTuplePrealloc(HashJoinTable hashtable, int batchno, size_t size)
{
ParallelHashJoinState *pstate = hashtable->parallel_state;
ParallelHashJoinBatchAccessor *batch = &hashtable->batches[batchno];
size_t want = Max(size, HASH_CHUNK_SIZE - HASH_CHUNK_HEADER_SIZE);
Assert(batchno > 0);
Assert(batchno < hashtable->nbatch);
Assert(size == MAXALIGN(size));
LWLockAcquire(&pstate->lock, LW_EXCLUSIVE);
/* Has another participant commanded us to help grow? */
if (pstate->growth == PHJ_GROWTH_NEED_MORE_BATCHES ||
pstate->growth == PHJ_GROWTH_NEED_MORE_BUCKETS)
{
ParallelHashGrowth growth = pstate->growth;
LWLockRelease(&pstate->lock);
if (growth == PHJ_GROWTH_NEED_MORE_BATCHES)
ExecParallelHashIncreaseNumBatches(hashtable);
else if (growth == PHJ_GROWTH_NEED_MORE_BUCKETS)
ExecParallelHashIncreaseNumBuckets(hashtable);
return false;
}
if (pstate->growth != PHJ_GROWTH_DISABLED &&
batch->at_least_one_chunk &&
(batch->shared->estimated_size + want + HASH_CHUNK_HEADER_SIZE
> pstate->space_allowed))
{
/*
* We have determined that this batch would exceed the space budget if
* loaded into memory. Command all participants to help repartition.
*/
batch->shared->space_exhausted = true;
pstate->growth = PHJ_GROWTH_NEED_MORE_BATCHES;
LWLockRelease(&pstate->lock);
return false;
}
batch->at_least_one_chunk = true;
batch->shared->estimated_size += want + HASH_CHUNK_HEADER_SIZE;
batch->preallocated = want;
LWLockRelease(&pstate->lock);
return true;
}
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