/*-------------------------------------------------------------------------
*
* nodeHashjoin.c
* Routines to handle hash join nodes
*
* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/executor/nodeHashjoin.c
*
* PARALLELISM
*
* Hash joins can participate in parallel query execution in several ways. A
* parallel-oblivious hash join is one where the node is unaware that it is
* part of a parallel plan. In this case, a copy of the inner plan is used to
* build a copy of the hash table in every backend, and the outer plan could
* either be built from a partial or complete path, so that the results of the
* hash join are correspondingly either partial or complete. A parallel-aware
* hash join is one that behaves differently, coordinating work between
* backends, and appears as Parallel Hash Join in EXPLAIN output. A Parallel
* Hash Join always appears with a Parallel Hash node.
*
* Parallel-aware hash joins use the same per-backend state machine to track
* progress through the hash join algorithm as parallel-oblivious hash joins.
* In a parallel-aware hash join, there is also a shared state machine that
* co-operating backends use to synchronize their local state machines and
* program counters. The shared state machine is managed with a Barrier IPC
* primitive. When all attached participants arrive at a barrier, the phase
* advances and all waiting participants are released.
*
* When a participant begins working on a parallel hash join, it must first
* figure out how much progress has already been made, because participants
* don't wait for each other to begin. For this reason there are switch
* statements at key points in the code where we have to synchronize our local
* state machine with the phase, and then jump to the correct part of the
* algorithm so that we can get started.
*
* One barrier called build_barrier is used to coordinate the hashing phases.
* The phase is represented by an integer which begins at zero and increments
* one by one, but in the code it is referred to by symbolic names as follows:
*
* PHJ_BUILD_ELECTING -- initial state
* PHJ_BUILD_ALLOCATING -- one sets up the batches and table 0
* PHJ_BUILD_HASHING_INNER -- all hash the inner rel
* PHJ_BUILD_HASHING_OUTER -- (multi-batch only) all hash the outer
* PHJ_BUILD_DONE -- building done, probing can begin
*
* While in the phase PHJ_BUILD_HASHING_INNER a separate pair of barriers may
* be used repeatedly as required to coordinate expansions in the number of
* batches or buckets. Their phases are as follows:
*
* PHJ_GROW_BATCHES_ELECTING -- initial state
* PHJ_GROW_BATCHES_ALLOCATING -- one allocates new batches
* PHJ_GROW_BATCHES_REPARTITIONING -- all repartition
* PHJ_GROW_BATCHES_FINISHING -- one cleans up, detects skew
*
* PHJ_GROW_BUCKETS_ELECTING -- initial state
* PHJ_GROW_BUCKETS_ALLOCATING -- one allocates new buckets
* PHJ_GROW_BUCKETS_REINSERTING -- all insert tuples
*
* If the planner got the number of batches and buckets right, those won't be
* necessary, but on the other hand we might finish up needing to expand the
* buckets or batches multiple times while hashing the inner relation to stay
* within our memory budget and load factor target. For that reason it's a
* separate pair of barriers using circular phases.
*
* The PHJ_BUILD_HASHING_OUTER phase is required only for multi-batch joins,
* because we need to divide the outer relation into batches up front in order
* to be able to process batches entirely independently. In contrast, the
* parallel-oblivious algorithm simply throws tuples 'forward' to 'later'
* batches whenever it encounters them while scanning and probing, which it
* can do because it processes batches in serial order.
*
* Once PHJ_BUILD_DONE is reached, backends then split up and process
* different batches, or gang up and work together on probing batches if there
* aren't enough to go around. For each batch there is a separate barrier
* with the following phases:
*
* PHJ_BATCH_ELECTING -- initial state
* PHJ_BATCH_ALLOCATING -- one allocates buckets
* PHJ_BATCH_LOADING -- all load the hash table from disk
* PHJ_BATCH_PROBING -- all probe
* PHJ_BATCH_DONE -- end
*
* Batch 0 is a special case, because it starts out in phase
* PHJ_BATCH_PROBING; populating batch 0's hash table is done during
* PHJ_BUILD_HASHING_INNER so we can skip loading.
*
* Initially we try to plan for a single-batch hash join using the combined
* hash_mem of all participants to create a large shared hash table. If that
* turns out either at planning or execution time to be impossible then we
* fall back to regular hash_mem sized hash tables.
*
* To avoid deadlocks, we never wait for any barrier unless it is known that
* all other backends attached to it are actively executing the node or have
* already arrived. Practically, that means that we never return a tuple
* while attached to a barrier, unless the barrier has reached its final
* state. In the slightly special case of the per-batch barrier, we return
* tuples while in PHJ_BATCH_PROBING phase, but that's OK because we use
* BarrierArriveAndDetach() to advance it to PHJ_BATCH_DONE without waiting.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup_details.h"
#include "access/parallel.h"
#include "executor/executor.h"
#include "executor/hashjoin.h"
#include "executor/nodeHash.h"
#include "executor/nodeHashjoin.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "utils/memutils.h"
#include "utils/sharedtuplestore.h"
/*
* States of the ExecHashJoin state machine
*/
#define HJ_BUILD_HASHTABLE 1
#define HJ_NEED_NEW_OUTER 2
#define HJ_SCAN_BUCKET 3
#define HJ_FILL_OUTER_TUPLE 4
#define HJ_FILL_INNER_TUPLES 5
#define HJ_NEED_NEW_BATCH 6
/* Returns true if doing null-fill on outer relation */
#define HJ_FILL_OUTER(hjstate) ((hjstate)->hj_NullInnerTupleSlot != NULL)
/* Returns true if doing null-fill on inner relation */
#define HJ_FILL_INNER(hjstate) ((hjstate)->hj_NullOuterTupleSlot != NULL)
static TupleTableSlot *ExecHashJoinOuterGetTuple(PlanState *outerNode,
HashJoinState *hjstate,
uint32 *hashvalue);
static TupleTableSlot *ExecParallelHashJoinOuterGetTuple(PlanState *outerNode,
HashJoinState *hjstate,
uint32 *hashvalue);
static TupleTableSlot *ExecHashJoinGetSavedTuple(HashJoinState *hjstate,
BufFile *file,
uint32 *hashvalue,
TupleTableSlot *tupleSlot);
static bool ExecHashJoinNewBatch(HashJoinState *hjstate);
static bool ExecParallelHashJoinNewBatch(HashJoinState *hjstate);
static void ExecParallelHashJoinPartitionOuter(HashJoinState *node);
/* ----------------------------------------------------------------
* ExecHashJoinImpl
*
* This function implements the Hybrid Hashjoin algorithm. It is marked
* with an always-inline attribute so that ExecHashJoin() and
* ExecParallelHashJoin() can inline it. Compilers that respect the
* attribute should create versions specialized for parallel == true and
* parallel == false with unnecessary branches removed.
*
* Note: the relation we build hash table on is the "inner"
* the other one is "outer".
* ----------------------------------------------------------------
*/
static pg_attribute_always_inline TupleTableSlot *
ExecHashJoinImpl(PlanState *pstate, bool parallel)
{
HashJoinState *node = castNode(HashJoinState, pstate);
PlanState *outerNode;
HashState *hashNode;
ExprState *joinqual;
ExprState *otherqual;
ExprContext *econtext;
HashJoinTable hashtable;
TupleTableSlot *outerTupleSlot;
uint32 hashvalue;
int batchno;
ParallelHashJoinState *parallel_state;
/*
* get information from HashJoin node
*/
joinqual = node->js.joinqual;
otherqual = node->js.ps.qual;
hashNode = (HashState *) innerPlanState(node);
outerNode = outerPlanState(node);
hashtable = node->hj_HashTable;
econtext = node->js.ps.ps_ExprContext;
parallel_state = hashNode->parallel_state;
/*
* Reset per-tuple memory context to free any expression evaluation
* storage allocated in the previous tuple cycle.
*/
ResetExprContext(econtext);
/*
* run the hash join state machine
*/
for (;;)
{
/*
* It's possible to iterate this loop many times before returning a
* tuple, in some pathological cases such as needing to move much of
* the current batch to a later batch. So let's check for interrupts
* each time through.
*/
CHECK_FOR_INTERRUPTS();
switch (node->hj_JoinState)
{
case HJ_BUILD_HASHTABLE:
/*
* First time through: build hash table for inner relation.
*/
Assert(hashtable == NULL);
/*
* If the outer relation is completely empty, and it's not
* right/full join, we can quit without building the hash
* table. However, for an inner join it is only a win to
* check this when the outer relation's startup cost is less
* than the projected cost of building the hash table.
* Otherwise it's best to build the hash table first and see
* if the inner relation is empty. (When it's a left join, we
* should always make this check, since we aren't going to be
* able to skip the join on the strength of an empty inner
* relation anyway.)
*
* If we are rescanning the join, we make use of information
* gained on the previous scan: don't bother to try the
* prefetch if the previous scan found the outer relation
* nonempty. This is not 100% reliable since with new
* parameters the outer relation might yield different
* results, but it's a good heuristic.
*
* The only way to make the check is to try to fetch a tuple
* from the outer plan node. If we succeed, we have to stash
* it away for later consumption by ExecHashJoinOuterGetTuple.
*/
if (HJ_FILL_INNER(node))
{
/* no chance to not build the hash table */
node->hj_FirstOuterTupleSlot = NULL;
}
else if (parallel)
{
/*
* The empty-outer optimization is not implemented for
* shared hash tables, because no one participant can
* determine that there are no outer tuples, and it's not
* yet clear that it's worth the synchronization overhead
* of reaching consensus to figure that out. So we have
* to build the hash table.
*/
node->hj_FirstOuterTupleSlot = NULL;
}
else if (HJ_FILL_OUTER(node) ||
(outerNode->plan->startup_cost < hashNode->ps.plan->total_cost &&
!node->hj_OuterNotEmpty))
{
node->hj_FirstOuterTupleSlot = ExecProcNode(outerNode);
if (TupIsNull(node->hj_FirstOuterTupleSlot))
{
node->hj_OuterNotEmpty = false;
return NULL;
}
else
node->hj_OuterNotEmpty = true;
}
else
node->hj_FirstOuterTupleSlot = NULL;
/*
* Create the hash table. If using Parallel Hash, then
* whoever gets here first will create the hash table and any
* later arrivals will merely attach to it.
*/
hashtable = ExecHashTableCreate(hashNode,
node->hj_HashOperators,
node->hj_Collations,
HJ_FILL_INNER(node));
node->hj_HashTable = hashtable;
/*
* Execute the Hash node, to build the hash table. If using
* Parallel Hash, then we'll try to help hashing unless we
* arrived too late.
*/
hashNode->hashtable = hashtable;
(void) MultiExecProcNode((PlanState *) hashNode);
/*
* If the inner relation is completely empty, and we're not
* doing a left outer join, we can quit without scanning the
* outer relation.
*/
if (hashtable->totalTuples == 0 && !HJ_FILL_OUTER(node))
return NULL;
/*
* need to remember whether nbatch has increased since we
* began scanning the outer relation
*/
hashtable->nbatch_outstart = hashtable->nbatch;
/*
* Reset OuterNotEmpty for scan. (It's OK if we fetched a
* tuple above, because ExecHashJoinOuterGetTuple will
* immediately set it again.)
*/
node->hj_OuterNotEmpty = false;
if (parallel)
{
Barrier *build_barrier;
build_barrier = ¶llel_state->build_barrier;
Assert(BarrierPhase(build_barrier) == PHJ_BUILD_HASHING_OUTER ||
BarrierPhase(build_barrier) == PHJ_BUILD_DONE);
if (BarrierPhase(build_barrier) == PHJ_BUILD_HASHING_OUTER)
{
/*
* If multi-batch, we need to hash the outer relation
* up front.
*/
if (hashtable->nbatch > 1)
ExecParallelHashJoinPartitionOuter(node);
BarrierArriveAndWait(build_barrier,
WAIT_EVENT_HASH_BUILD_HASH_OUTER);
}
Assert(BarrierPhase(build_barrier) == PHJ_BUILD_DONE);
/* Each backend should now select a batch to work on. */
hashtable->curbatch = -1;
node->hj_JoinState = HJ_NEED_NEW_BATCH;
continue;
}
else
node->hj_JoinState = HJ_NEED_NEW_OUTER;
/* FALL THRU */
case HJ_NEED_NEW_OUTER:
/*
* We don't have an outer tuple, try to get the next one
*/
if (parallel)
outerTupleSlot =
ExecParallelHashJoinOuterGetTuple(outerNode, node,
&hashvalue);
else
outerTupleSlot =
ExecHashJoinOuterGetTuple(outerNode, node, &hashvalue);
if (TupIsNull(outerTupleSlot))
{
/* end of batch, or maybe whole join */
if (HJ_FILL_INNER(node))
{
/* set up to scan for unmatched inner tuples */
ExecPrepHashTableForUnmatched(node);
node->hj_JoinState = HJ_FILL_INNER_TUPLES;
}
else
node->hj_JoinState = HJ_NEED_NEW_BATCH;
continue;
}
econtext->ecxt_outertuple = outerTupleSlot;
node->hj_MatchedOuter = false;
/*
* Find the corresponding bucket for this tuple in the main
* hash table or skew hash table.
*/
node->hj_CurHashValue = hashvalue;
ExecHashGetBucketAndBatch(hashtable, hashvalue,
&node->hj_CurBucketNo, &batchno);
node->hj_CurSkewBucketNo = ExecHashGetSkewBucket(hashtable,
hashvalue);
node->hj_CurTuple = NULL;
/*
* The tuple might not belong to the current batch (where
* "current batch" includes the skew buckets if any).
*/
if (batchno != hashtable->curbatch &&
node->hj_CurSkewBucketNo == INVALID_SKEW_BUCKET_NO)
{
bool shouldFree;
MinimalTuple mintuple = ExecFetchSlotMinimalTuple(outerTupleSlot,
&shouldFree);
/*
* Need to postpone this outer tuple to a later batch.
* Save it in the corresponding outer-batch file.
*/
Assert(parallel_state == NULL);
Assert(batchno > hashtable->curbatch);
ExecHashJoinSaveTuple(mintuple, hashvalue,
&hashtable->outerBatchFile[batchno]);
if (shouldFree)
heap_free_minimal_tuple(mintuple);
/* Loop around, staying in HJ_NEED_NEW_OUTER state */
continue;
}
/* OK, let's scan the bucket for matches */
node->hj_JoinState = HJ_SCAN_BUCKET;
/* FALL THRU */
case HJ_SCAN_BUCKET:
/*
* Scan the selected hash bucket for matches to current outer
*/
if (parallel)
{
if (!ExecParallelScanHashBucket(node, econtext))
{
/* out of matches; check for possible outer-join fill */
node->hj_JoinState = HJ_FILL_OUTER_TUPLE;
continue;
}
}
else
{
if (!ExecScanHashBucket(node, econtext))
{
/* out of matches; check for possible outer-join fill */
node->hj_JoinState = HJ_FILL_OUTER_TUPLE;
continue;
}
}
/*
* We've got a match, but still need to test non-hashed quals.
* ExecScanHashBucket already set up all the state needed to
* call ExecQual.
*
* If we pass the qual, then save state for next call and have
* ExecProject form the projection, store it in the tuple
* table, and return the slot.
*
* Only the joinquals determine tuple match status, but all
* quals must pass to actually return the tuple.
*/
if (joinqual == NULL || ExecQual(joinqual, econtext))
{
node->hj_MatchedOuter = true;
if (parallel)
{
/*
* Full/right outer joins are currently not supported
* for parallel joins, so we don't need to set the
* match bit. Experiments show that it's worth
* avoiding the shared memory traffic on large
* systems.
*/
Assert(!HJ_FILL_INNER(node));
}
else
{
/*
* This is really only needed if HJ_FILL_INNER(node),
* but we'll avoid the branch and just set it always.
*/
HeapTupleHeaderSetMatch(HJTUPLE_MINTUPLE(node->hj_CurTuple));
}
/* In an antijoin, we never return a matched tuple */
if (node->js.jointype == JOIN_ANTI)
{
node->hj_JoinState = HJ_NEED_NEW_OUTER;
continue;
}
/*
* If we only need to join to the first matching inner
* tuple, then consider returning this one, but after that
* continue with next outer tuple.
*/
if (node->js.single_match)
node->hj_JoinState = HJ_NEED_NEW_OUTER;
if (otherqual == NULL || ExecQual(otherqual, econtext))
return ExecProject(node->js.ps.ps_ProjInfo);
else
InstrCountFiltered2(node, 1);
}
else
InstrCountFiltered1(node, 1);
break;
case HJ_FILL_OUTER_TUPLE:
/*
* The current outer tuple has run out of matches, so check
* whether to emit a dummy outer-join tuple. Whether we emit
* one or not, the next state is NEED_NEW_OUTER.
*/
node->hj_JoinState = HJ_NEED_NEW_OUTER;
if (!node->hj_MatchedOuter &&
HJ_FILL_OUTER(node))
{
/*
* Generate a fake join tuple with nulls for the inner
* tuple, and return it if it passes the non-join quals.
*/
econtext->ecxt_innertuple = node->hj_NullInnerTupleSlot;
if (otherqual == NULL || ExecQual(otherqual, econtext))
return ExecProject(node->js.ps.ps_ProjInfo);
else
InstrCountFiltered2(node, 1);
}
break;
case HJ_FILL_INNER_TUPLES:
/*
* We have finished a batch, but we are doing right/full join,
* so any unmatched inner tuples in the hashtable have to be
* emitted before we continue to the next batch.
*/
if (!ExecScanHashTableForUnmatched(node, econtext))
{
/* no more unmatched tuples */
node->hj_JoinState = HJ_NEED_NEW_BATCH;
continue;
}
/*
* Generate a fake join tuple with nulls for the outer tuple,
* and return it if it passes the non-join quals.
*/
econtext->ecxt_outertuple = node->hj_NullOuterTupleSlot;
if (otherqual == NULL || ExecQual(otherqual, econtext))
return ExecProject(node->js.ps.ps_ProjInfo);
else
InstrCountFiltered2(node, 1);
break;
case HJ_NEED_NEW_BATCH:
/*
* Try to advance to next batch. Done if there are no more.
*/
if (parallel)
{
if (!ExecParallelHashJoinNewBatch(node))
return NULL; /* end of parallel-aware join */
}
else
{
if (!ExecHashJoinNewBatch(node))
return NULL; /* end of parallel-oblivious join */
}
node->hj_JoinState = HJ_NEED_NEW_OUTER;
break;
default:
elog(ERROR, "unrecognized hashjoin state: %d",
(int) node->hj_JoinState);
}
}
}
/* ----------------------------------------------------------------
* ExecHashJoin
*
* Parallel-oblivious version.
* ----------------------------------------------------------------
*/
static TupleTableSlot * /* return: a tuple or NULL */
ExecHashJoin(PlanState *pstate)
{
/*
* On sufficiently smart compilers this should be inlined with the
* parallel-aware branches removed.
*/
return ExecHashJoinImpl(pstate, false);
}
/* ----------------------------------------------------------------
* ExecParallelHashJoin
*
* Parallel-aware version.
* ----------------------------------------------------------------
*/
static TupleTableSlot * /* return: a tuple or NULL */
ExecParallelHashJoin(PlanState *pstate)
{
/*
* On sufficiently smart compilers this should be inlined with the
* parallel-oblivious branches removed.
*/
return ExecHashJoinImpl(pstate, true);
}
/* ----------------------------------------------------------------
* ExecInitHashJoin
*
* Init routine for HashJoin node.
* ----------------------------------------------------------------
*/
HashJoinState *
ExecInitHashJoin(HashJoin *node, EState *estate, int eflags)
{
HashJoinState *hjstate;
Plan *outerNode;
Hash *hashNode;
TupleDesc outerDesc,
innerDesc;
const TupleTableSlotOps *ops;
/* check for unsupported flags */
Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
/*
* create state structure
*/
hjstate = makeNode(HashJoinState);
hjstate->js.ps.plan = (Plan *) node;
hjstate->js.ps.state = estate;
/*
* See ExecHashJoinInitializeDSM() and ExecHashJoinInitializeWorker()
* where this function may be replaced with a parallel version, if we
* managed to launch a parallel query.
*/
hjstate->js.ps.ExecProcNode = ExecHashJoin;
hjstate->js.jointype = node->join.jointype;
/*
* Miscellaneous initialization
*
* create expression context for node
*/
ExecAssignExprContext(estate, &hjstate->js.ps);
/*
* initialize child nodes
*
* Note: we could suppress the REWIND flag for the inner input, which
* would amount to betting that the hash will be a single batch. Not
* clear if this would be a win or not.
*/
outerNode = outerPlan(node);
hashNode = (Hash *) innerPlan(node);
outerPlanState(hjstate) = ExecInitNode(outerNode, estate, eflags);
outerDesc = ExecGetResultType(outerPlanState(hjstate));
innerPlanState(hjstate) = ExecInitNode((Plan *) hashNode, estate, eflags);
innerDesc = ExecGetResultType(innerPlanState(hjstate));
/*
* Initialize result slot, type and projection.
*/
ExecInitResultTupleSlotTL(&hjstate->js.ps, &TTSOpsVirtual);
ExecAssignProjectionInfo(&hjstate->js.ps, NULL);
/*
* tuple table initialization
*/
ops = ExecGetResultSlotOps(outerPlanState(hjstate), NULL);
hjstate->hj_OuterTupleSlot = ExecInitExtraTupleSlot(estate, outerDesc,
ops);
/*
* detect whether we need only consider the first matching inner tuple
*/
hjstate->js.single_match = (node->join.inner_unique ||
node->join.jointype == JOIN_SEMI);
/* set up null tuples for outer joins, if needed */
switch (node->join.jointype)
{
case JOIN_INNER:
case JOIN_SEMI:
break;
case JOIN_LEFT:
case JOIN_ANTI:
hjstate->hj_NullInnerTupleSlot =
ExecInitNullTupleSlot(estate, innerDesc, &TTSOpsVirtual);
break;
case JOIN_RIGHT:
hjstate->hj_NullOuterTupleSlot =
ExecInitNullTupleSlot(estate, outerDesc, &TTSOpsVirtual);
break;
case JOIN_FULL:
hjstate->hj_NullOuterTupleSlot =
ExecInitNullTupleSlot(estate, outerDesc, &TTSOpsVirtual);
hjstate->hj_NullInnerTupleSlot =
ExecInitNullTupleSlot(estate, innerDesc, &TTSOpsVirtual);
break;
default:
elog(ERROR, "unrecognized join type: %d",
(int) node->join.jointype);
}
/*
* now for some voodoo. our temporary tuple slot is actually the result
* tuple slot of the Hash node (which is our inner plan). we can do this
* because Hash nodes don't return tuples via ExecProcNode() -- instead
* the hash join node uses ExecScanHashBucket() to get at the contents of
* the hash table. -cim 6/9/91
*/
{
HashState *hashstate = (HashState *) innerPlanState(hjstate);
TupleTableSlot *slot = hashstate->ps.ps_ResultTupleSlot;
hjstate->hj_HashTupleSlot = slot;
}
/*
* initialize child expressions
*/
hjstate->js.ps.qual =
ExecInitQual(node->join.plan.qual, (PlanState *) hjstate);
hjstate->js.joinqual =
ExecInitQual(node->join.joinqual, (PlanState *) hjstate);
hjstate->hashclauses =
ExecInitQual(node->hashclauses, (PlanState *) hjstate);
/*
* initialize hash-specific info
*/
hjstate->hj_HashTable = NULL;
hjstate->hj_FirstOuterTupleSlot = NULL;
hjstate->hj_CurHashValue = 0;
hjstate->hj_CurBucketNo = 0;
hjstate->hj_CurSkewBucketNo = INVALID_SKEW_BUCKET_NO;
hjstate->hj_CurTuple = NULL;
hjstate->hj_OuterHashKeys = ExecInitExprList(node->hashkeys,
(PlanState *) hjstate);
hjstate->hj_HashOperators = node->hashoperators;
hjstate->hj_Collations = node->hashcollations;
hjstate->hj_JoinState = HJ_BUILD_HASHTABLE;
hjstate->hj_MatchedOuter = false;
hjstate->hj_OuterNotEmpty = false;
return hjstate;
}
/* ----------------------------------------------------------------
* ExecEndHashJoin
*
* clean up routine for HashJoin node
* ----------------------------------------------------------------
*/
void
ExecEndHashJoin(HashJoinState *node)
{
/*
* Free hash table
*/
if (node->hj_HashTable)
{
ExecHashTableDestroy(node->hj_HashTable);
node->hj_HashTable = NULL;
}
/*
* Free the exprcontext
*/
ExecFreeExprContext(&node->js.ps);
/*
* clean out the tuple table
*/
ExecClearTuple(node->js.ps.ps_ResultTupleSlot);
ExecClearTuple(node->hj_OuterTupleSlot);
ExecClearTuple(node->hj_HashTupleSlot);
/*
* clean up subtrees
*/
ExecEndNode(outerPlanState(node));
ExecEndNode(innerPlanState(node));
}
/*
* ExecHashJoinOuterGetTuple
*
* get the next outer tuple for a parallel oblivious hashjoin: either by
* executing the outer plan node in the first pass, or from the temp
* files for the hashjoin batches.
*
* Returns a null slot if no more outer tuples (within the current batch).
*
* On success, the tuple's hash value is stored at *hashvalue --- this is
* either originally computed, or re-read from the temp file.
*/
static TupleTableSlot *
ExecHashJoinOuterGetTuple(PlanState *outerNode,
HashJoinState *hjstate,
uint32 *hashvalue)
{
HashJoinTable hashtable = hjstate->hj_HashTable;
int curbatch = hashtable->curbatch;
TupleTableSlot *slot;
if (curbatch == 0) /* if it is the first pass */
{
/*
* Check to see if first outer tuple was already fetched by
* ExecHashJoin() and not used yet.
*/
slot = hjstate->hj_FirstOuterTupleSlot;
if (!TupIsNull(slot))
hjstate->hj_FirstOuterTupleSlot = NULL;
else
slot = ExecProcNode(outerNode);
while (!TupIsNull(slot))
{
/*
* We have to compute the tuple's hash value.
*/
ExprContext *econtext = hjstate->js.ps.ps_ExprContext;
econtext->ecxt_outertuple = slot;
if (ExecHashGetHashValue(hashtable, econtext,
hjstate->hj_OuterHashKeys,
true, /* outer tuple */
HJ_FILL_OUTER(hjstate),
hashvalue))
{
/* remember outer relation is not empty for possible rescan */
hjstate->hj_OuterNotEmpty = true;
return slot;
}
/*
* That tuple couldn't match because of a NULL, so discard it and
* continue with the next one.
*/
slot = ExecProcNode(outerNode);
}
}
else if (curbatch < hashtable->nbatch)
{
BufFile *file = hashtable->outerBatchFile[curbatch];
/*
* In outer-join cases, we could get here even though the batch file
* is empty.
*/
if (file == NULL)
return NULL;
slot = ExecHashJoinGetSavedTuple(hjstate,
file,
hashvalue,
hjstate->hj_OuterTupleSlot);
if (!TupIsNull(slot))
return slot;
}
/* End of this batch */
return NULL;
}
/*
* ExecHashJoinOuterGetTuple variant for the parallel case.
*/
static TupleTableSlot *
ExecParallelHashJoinOuterGetTuple(PlanState *outerNode,
HashJoinState *hjstate,
uint32 *hashvalue)
{
HashJoinTable hashtable = hjstate->hj_HashTable;
int curbatch = hashtable->curbatch;
TupleTableSlot *slot;
/*
* In the Parallel Hash case we only run the outer plan directly for
* single-batch hash joins. Otherwise we have to go to batch files, even
* for batch 0.
*/
if (curbatch == 0 && hashtable->nbatch == 1)
{
slot = ExecProcNode(outerNode);
while (!TupIsNull(slot))
{
ExprContext *econtext = hjstate->js.ps.ps_ExprContext;
econtext->ecxt_outertuple = slot;
if (ExecHashGetHashValue(hashtable, econtext,
hjstate->hj_OuterHashKeys,
true, /* outer tuple */
HJ_FILL_OUTER(hjstate),
hashvalue))
return slot;
/*
* That tuple couldn't match because of a NULL, so discard it and
* continue with the next one.
*/
slot = ExecProcNode(outerNode);
}
}
else if (curbatch < hashtable->nbatch)
{
MinimalTuple tuple;
tuple = sts_parallel_scan_next(hashtable->batches[curbatch].outer_tuples,
hashvalue);
if (tuple != NULL)
{
ExecForceStoreMinimalTuple(tuple,
hjstate->hj_OuterTupleSlot,
false);
slot = hjstate->hj_OuterTupleSlot;
return slot;
}
else
ExecClearTuple(hjstate->hj_OuterTupleSlot);
}
/* End of this batch */
return NULL;
}
/*
* ExecHashJoinNewBatch
* switch to a new hashjoin batch
*
* Returns true if successful, false if there are no more batches.
*/
static bool
ExecHashJoinNewBatch(HashJoinState *hjstate)
{
HashJoinTable hashtable = hjstate->hj_HashTable;
int nbatch;
int curbatch;
BufFile *innerFile;
TupleTableSlot *slot;
uint32 hashvalue;
nbatch = hashtable->nbatch;
curbatch = hashtable->curbatch;
if (curbatch > 0)
{
/*
* We no longer need the previous outer batch file; close it right
* away to free disk space.
*/
if (hashtable->outerBatchFile[curbatch])
BufFileClose(hashtable->outerBatchFile[curbatch]);
hashtable->outerBatchFile[curbatch] = NULL;
}
else /* we just finished the first batch */
{
/*
* Reset some of the skew optimization state variables, since we no
* longer need to consider skew tuples after the first batch. The
* memory context reset we are about to do will release the skew
* hashtable itself.
*/
hashtable->skewEnabled = false;
hashtable->skewBucket = NULL;
hashtable->skewBucketNums = NULL;
hashtable->nSkewBuckets = 0;
hashtable->spaceUsedSkew = 0;
}
/*
* We can always skip over any batches that are completely empty on both
* sides. We can sometimes skip over batches that are empty on only one
* side, but there are exceptions:
*
* 1. In a left/full outer join, we have to process outer batches even if
* the inner batch is empty. Similarly, in a right/full outer join, we
* have to process inner batches even if the outer batch is empty.
*
* 2. If we have increased nbatch since the initial estimate, we have to
* scan inner batches since they might contain tuples that need to be
* reassigned to later inner batches.
*
* 3. Similarly, if we have increased nbatch since starting the outer
* scan, we have to rescan outer batches in case they contain tuples that
* need to be reassigned.
*/
curbatch++;
while (curbatch < nbatch &&
(hashtable->outerBatchFile[curbatch] == NULL ||
hashtable->innerBatchFile[curbatch] == NULL))
{
if (hashtable->outerBatchFile[curbatch] &&
HJ_FILL_OUTER(hjstate))
break; /* must process due to rule 1 */
if (hashtable->innerBatchFile[curbatch] &&
HJ_FILL_INNER(hjstate))
break; /* must process due to rule 1 */
if (hashtable->innerBatchFile[curbatch] &&
nbatch != hashtable->nbatch_original)
break; /* must process due to rule 2 */
if (hashtable->outerBatchFile[curbatch] &&
nbatch != hashtable->nbatch_outstart)
break; /* must process due to rule 3 */
/* We can ignore this batch. */
/* Release associated temp files right away. */
if (hashtable->innerBatchFile[curbatch])
BufFileClose(hashtable->innerBatchFile[curbatch]);
hashtable->innerBatchFile[curbatch] = NULL;
if (hashtable->outerBatchFile[curbatch])
BufFileClose(hashtable->outerBatchFile[curbatch]);
hashtable->outerBatchFile[curbatch] = NULL;
curbatch++;
}
if (curbatch >= nbatch)
return false; /* no more batches */
hashtable->curbatch = curbatch;
/*
* Reload the hash table with the new inner batch (which could be empty)
*/
ExecHashTableReset(hashtable);
innerFile = hashtable->innerBatchFile[curbatch];
if (innerFile != NULL)
{
if (BufFileSeek(innerFile, 0, 0L, SEEK_SET))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not rewind hash-join temporary file")));
while ((slot = ExecHashJoinGetSavedTuple(hjstate,
innerFile,
&hashvalue,
hjstate->hj_HashTupleSlot)))
{
/*
* NOTE: some tuples may be sent to future batches. Also, it is
* possible for hashtable->nbatch to be increased here!
*/
ExecHashTableInsert(hashtable, slot, hashvalue);
}
/*
* after we build the hash table, the inner batch file is no longer
* needed
*/
BufFileClose(innerFile);
hashtable->innerBatchFile[curbatch] = NULL;
}
/*
* Rewind outer batch file (if present), so that we can start reading it.
*/
if (hashtable->outerBatchFile[curbatch] != NULL)
{
if (BufFileSeek(hashtable->outerBatchFile[curbatch], 0, 0L, SEEK_SET))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not rewind hash-join temporary file")));
}
return true;
}
/*
* Choose a batch to work on, and attach to it. Returns true if successful,
* false if there are no more batches.
*/
static bool
ExecParallelHashJoinNewBatch(HashJoinState *hjstate)
{
HashJoinTable hashtable = hjstate->hj_HashTable;
int start_batchno;
int batchno;
/*
* If we started up so late that the batch tracking array has been freed
* already by ExecHashTableDetach(), then we are finished. See also
* ExecParallelHashEnsureBatchAccessors().
*/
if (hashtable->batches == NULL)
return false;
/*
* If we were already attached to a batch, remember not to bother checking
* it again, and detach from it (possibly freeing the hash table if we are
* last to detach).
*/
if (hashtable->curbatch >= 0)
{
hashtable->batches[hashtable->curbatch].done = true;
ExecHashTableDetachBatch(hashtable);
}
/*
* Search for a batch that isn't done. We use an atomic counter to start
* our search at a different batch in every participant when there are
* more batches than participants.
*/
batchno = start_batchno =
pg_atomic_fetch_add_u32(&hashtable->parallel_state->distributor, 1) %
hashtable->nbatch;
do
{
uint32 hashvalue;
MinimalTuple tuple;
TupleTableSlot *slot;
if (!hashtable->batches[batchno].done)
{
SharedTuplestoreAccessor *inner_tuples;
Barrier *batch_barrier =
&hashtable->batches[batchno].shared->batch_barrier;
switch (BarrierAttach(batch_barrier))
{
case PHJ_BATCH_ELECTING:
/* One backend allocates the hash table. */
if (BarrierArriveAndWait(batch_barrier,
WAIT_EVENT_HASH_BATCH_ELECT))
ExecParallelHashTableAlloc(hashtable, batchno);
/* Fall through. */
case PHJ_BATCH_ALLOCATING:
/* Wait for allocation to complete. */
BarrierArriveAndWait(batch_barrier,
WAIT_EVENT_HASH_BATCH_ALLOCATE);
/* Fall through. */
case PHJ_BATCH_LOADING:
/* Start (or join in) loading tuples. */
ExecParallelHashTableSetCurrentBatch(hashtable, batchno);
inner_tuples = hashtable->batches[batchno].inner_tuples;
sts_begin_parallel_scan(inner_tuples);
while ((tuple = sts_parallel_scan_next(inner_tuples,
&hashvalue)))
{
ExecForceStoreMinimalTuple(tuple,
hjstate->hj_HashTupleSlot,
false);
slot = hjstate->hj_HashTupleSlot;
ExecParallelHashTableInsertCurrentBatch(hashtable, slot,
hashvalue);
}
sts_end_parallel_scan(inner_tuples);
BarrierArriveAndWait(batch_barrier,
WAIT_EVENT_HASH_BATCH_LOAD);
/* Fall through. */
case PHJ_BATCH_PROBING:
/*
* This batch is ready to probe. Return control to
* caller. We stay attached to batch_barrier so that the
* hash table stays alive until everyone's finished
* probing it, but no participant is allowed to wait at
* this barrier again (or else a deadlock could occur).
* All attached participants must eventually call
* BarrierArriveAndDetach() so that the final phase
* PHJ_BATCH_DONE can be reached.
*/
ExecParallelHashTableSetCurrentBatch(hashtable, batchno);
sts_begin_parallel_scan(hashtable->batches[batchno].outer_tuples);
return true;
case PHJ_BATCH_DONE:
/*
* Already done. Detach and go around again (if any
* remain).
*/
BarrierDetach(batch_barrier);
hashtable->batches[batchno].done = true;
hashtable->curbatch = -1;
break;
default:
elog(ERROR, "unexpected batch phase %d",
BarrierPhase(batch_barrier));
}
}
batchno = (batchno + 1) % hashtable->nbatch;
} while (batchno != start_batchno);
return false;
}
/*
* ExecHashJoinSaveTuple
* save a tuple to a batch file.
*
* The data recorded in the file for each tuple is its hash value,
* then the tuple in MinimalTuple format.
*
* Note: it is important always to call this in the regular executor
* context, not in a shorter-lived context; else the temp file buffers
* will get messed up.
*/
void
ExecHashJoinSaveTuple(MinimalTuple tuple, uint32 hashvalue,
BufFile **fileptr)
{
BufFile *file = *fileptr;
if (file == NULL)
{
/* First write to this batch file, so open it. */
file = BufFileCreateTemp(false);
*fileptr = file;
}
BufFileWrite(file, (void *) &hashvalue, sizeof(uint32));
BufFileWrite(file, (void *) tuple, tuple->t_len);
}
/*
* ExecHashJoinGetSavedTuple
* read the next tuple from a batch file. Return NULL if no more.
*
* On success, *hashvalue is set to the tuple's hash value, and the tuple
* itself is stored in the given slot.
*/
static TupleTableSlot *
ExecHashJoinGetSavedTuple(HashJoinState *hjstate,
BufFile *file,
uint32 *hashvalue,
TupleTableSlot *tupleSlot)
{
uint32 header[2];
size_t nread;
MinimalTuple tuple;
/*
* We check for interrupts here because this is typically taken as an
* alternative code path to an ExecProcNode() call, which would include
* such a check.
*/
CHECK_FOR_INTERRUPTS();
/*
* Since both the hash value and the MinimalTuple length word are uint32,
* we can read them both in one BufFileRead() call without any type
* cheating.
*/
nread = BufFileRead(file, (void *) header, sizeof(header));
if (nread == 0) /* end of file */
{
ExecClearTuple(tupleSlot);
return NULL;
}
if (nread != sizeof(header))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from hash-join temporary file: read only %zu of %zu bytes",
nread, sizeof(header))));
*hashvalue = header[0];
tuple = (MinimalTuple) palloc(header[1]);
tuple->t_len = header[1];
nread = BufFileRead(file,
(void *) ((char *) tuple + sizeof(uint32)),
header[1] - sizeof(uint32));
if (nread != header[1] - sizeof(uint32))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from hash-join temporary file: read only %zu of %zu bytes",
nread, header[1] - sizeof(uint32))));
ExecForceStoreMinimalTuple(tuple, tupleSlot, true);
return tupleSlot;
}
void
ExecReScanHashJoin(HashJoinState *node)
{
PlanState *outerPlan = outerPlanState(node);
PlanState *innerPlan = innerPlanState(node);
/*
* In a multi-batch join, we currently have to do rescans the hard way,
* primarily because batch temp files may have already been released. But
* if it's a single-batch join, and there is no parameter change for the
* inner subnode, then we can just re-use the existing hash table without
* rebuilding it.
*/
if (node->hj_HashTable != NULL)
{
if (node->hj_HashTable->nbatch == 1 &&
innerPlan->chgParam == NULL)
{
/*
* Okay to reuse the hash table; needn't rescan inner, either.
*
* However, if it's a right/full join, we'd better reset the
* inner-tuple match flags contained in the table.
*/
if (HJ_FILL_INNER(node))
ExecHashTableResetMatchFlags(node->hj_HashTable);
/*
* Also, we need to reset our state about the emptiness of the
* outer relation, so that the new scan of the outer will update
* it correctly if it turns out to be empty this time. (There's no
* harm in clearing it now because ExecHashJoin won't need the
* info. In the other cases, where the hash table doesn't exist
* or we are destroying it, we leave this state alone because
* ExecHashJoin will need it the first time through.)
*/
node->hj_OuterNotEmpty = false;
/* ExecHashJoin can skip the BUILD_HASHTABLE step */
node->hj_JoinState = HJ_NEED_NEW_OUTER;
}
else
{
/* must destroy and rebuild hash table */
HashState *hashNode = castNode(HashState, innerPlan);
Assert(hashNode->hashtable == node->hj_HashTable);
/* accumulate stats from old hash table, if wanted */
/* (this should match ExecShutdownHash) */
if (hashNode->ps.instrument && !hashNode->hinstrument)
hashNode->hinstrument = (HashInstrumentation *)
palloc0(sizeof(HashInstrumentation));
if (hashNode->hinstrument)
ExecHashAccumInstrumentation(hashNode->hinstrument,
hashNode->hashtable);
/* for safety, be sure to clear child plan node's pointer too */
hashNode->hashtable = NULL;
ExecHashTableDestroy(node->hj_HashTable);
node->hj_HashTable = NULL;
node->hj_JoinState = HJ_BUILD_HASHTABLE;
/*
* if chgParam of subnode is not null then plan will be re-scanned
* by first ExecProcNode.
*/
if (innerPlan->chgParam == NULL)
ExecReScan(innerPlan);
}
}
/* Always reset intra-tuple state */
node->hj_CurHashValue = 0;
node->hj_CurBucketNo = 0;
node->hj_CurSkewBucketNo = INVALID_SKEW_BUCKET_NO;
node->hj_CurTuple = NULL;
node->hj_MatchedOuter = false;
node->hj_FirstOuterTupleSlot = NULL;
/*
* if chgParam of subnode is not null then plan will be re-scanned by
* first ExecProcNode.
*/
if (outerPlan->chgParam == NULL)
ExecReScan(outerPlan);
}
void
ExecShutdownHashJoin(HashJoinState *node)
{
if (node->hj_HashTable)
{
/*
* Detach from shared state before DSM memory goes away. This makes
* sure that we don't have any pointers into DSM memory by the time
* ExecEndHashJoin runs.
*/
ExecHashTableDetachBatch(node->hj_HashTable);
ExecHashTableDetach(node->hj_HashTable);
}
}
static void
ExecParallelHashJoinPartitionOuter(HashJoinState *hjstate)
{
PlanState *outerState = outerPlanState(hjstate);
ExprContext *econtext = hjstate->js.ps.ps_ExprContext;
HashJoinTable hashtable = hjstate->hj_HashTable;
TupleTableSlot *slot;
uint32 hashvalue;
int i;
Assert(hjstate->hj_FirstOuterTupleSlot == NULL);
/* Execute outer plan, writing all tuples to shared tuplestores. */
for (;;)
{
slot = ExecProcNode(outerState);
if (TupIsNull(slot))
break;
econtext->ecxt_outertuple = slot;
if (ExecHashGetHashValue(hashtable, econtext,
hjstate->hj_OuterHashKeys,
true, /* outer tuple */
HJ_FILL_OUTER(hjstate),
&hashvalue))
{
int batchno;
int bucketno;
bool shouldFree;
MinimalTuple mintup = ExecFetchSlotMinimalTuple(slot, &shouldFree);
ExecHashGetBucketAndBatch(hashtable, hashvalue, &bucketno,
&batchno);
sts_puttuple(hashtable->batches[batchno].outer_tuples,
&hashvalue, mintup);
if (shouldFree)
heap_free_minimal_tuple(mintup);
}
CHECK_FOR_INTERRUPTS();
}
/* Make sure all outer partitions are readable by any backend. */
for (i = 0; i < hashtable->nbatch; ++i)
sts_end_write(hashtable->batches[i].outer_tuples);
}
void
ExecHashJoinEstimate(HashJoinState *state, ParallelContext *pcxt)
{
shm_toc_estimate_chunk(&pcxt->estimator, sizeof(ParallelHashJoinState));
shm_toc_estimate_keys(&pcxt->estimator, 1);
}
void
ExecHashJoinInitializeDSM(HashJoinState *state, ParallelContext *pcxt)
{
int plan_node_id = state->js.ps.plan->plan_node_id;
HashState *hashNode;
ParallelHashJoinState *pstate;
/*
* Disable shared hash table mode if we failed to create a real DSM
* segment, because that means that we don't have a DSA area to work with.
*/
if (pcxt->seg == NULL)
return;
ExecSetExecProcNode(&state->js.ps, ExecParallelHashJoin);
/*
* Set up the state needed to coordinate access to the shared hash
* table(s), using the plan node ID as the toc key.
*/
pstate = shm_toc_allocate(pcxt->toc, sizeof(ParallelHashJoinState));
shm_toc_insert(pcxt->toc, plan_node_id, pstate);
/*
* Set up the shared hash join state with no batches initially.
* ExecHashTableCreate() will prepare at least one later and set nbatch
* and space_allowed.
*/
pstate->nbatch = 0;
pstate->space_allowed = 0;
pstate->batches = InvalidDsaPointer;
pstate->old_batches = InvalidDsaPointer;
pstate->nbuckets = 0;
pstate->growth = PHJ_GROWTH_OK;
pstate->chunk_work_queue = InvalidDsaPointer;
pg_atomic_init_u32(&pstate->distributor, 0);
pstate->nparticipants = pcxt->nworkers + 1;
pstate->total_tuples = 0;
LWLockInitialize(&pstate->lock,
LWTRANCHE_PARALLEL_HASH_JOIN);
BarrierInit(&pstate->build_barrier, 0);
BarrierInit(&pstate->grow_batches_barrier, 0);
BarrierInit(&pstate->grow_buckets_barrier, 0);
/* Set up the space we'll use for shared temporary files. */
SharedFileSetInit(&pstate->fileset, pcxt->seg);
/* Initialize the shared state in the hash node. */
hashNode = (HashState *) innerPlanState(state);
hashNode->parallel_state = pstate;
}
/* ----------------------------------------------------------------
* ExecHashJoinReInitializeDSM
*
* Reset shared state before beginning a fresh scan.
* ----------------------------------------------------------------
*/
void
ExecHashJoinReInitializeDSM(HashJoinState *state, ParallelContext *cxt)
{
int plan_node_id = state->js.ps.plan->plan_node_id;
ParallelHashJoinState *pstate =
shm_toc_lookup(cxt->toc, plan_node_id, false);
/*
* It would be possible to reuse the shared hash table in single-batch
* cases by resetting and then fast-forwarding build_barrier to
* PHJ_BUILD_DONE and batch 0's batch_barrier to PHJ_BATCH_PROBING, but
* currently shared hash tables are already freed by now (by the last
* participant to detach from the batch). We could consider keeping it
* around for single-batch joins. We'd also need to adjust
* finalize_plan() so that it doesn't record a dummy dependency for
* Parallel Hash nodes, preventing the rescan optimization. For now we
* don't try.
*/
/* Detach, freeing any remaining shared memory. */
if (state->hj_HashTable != NULL)
{
ExecHashTableDetachBatch(state->hj_HashTable);
ExecHashTableDetach(state->hj_HashTable);
}
/* Clear any shared batch files. */
SharedFileSetDeleteAll(&pstate->fileset);
/* Reset build_barrier to PHJ_BUILD_ELECTING so we can go around again. */
BarrierInit(&pstate->build_barrier, 0);
}
void
ExecHashJoinInitializeWorker(HashJoinState *state,
ParallelWorkerContext *pwcxt)
{
HashState *hashNode;
int plan_node_id = state->js.ps.plan->plan_node_id;
ParallelHashJoinState *pstate =
shm_toc_lookup(pwcxt->toc, plan_node_id, false);
/* Attach to the space for shared temporary files. */
SharedFileSetAttach(&pstate->fileset, pwcxt->seg);
/* Attach to the shared state in the hash node. */
hashNode = (HashState *) innerPlanState(state);
hashNode->parallel_state = pstate;
ExecSetExecProcNode(&state->js.ps, ExecParallelHashJoin);
}