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Fix EXPLAIN ANALYZE of hash join when the leader doesn't participate.

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If a hash join appears in a parallel query, there may be no hash table
available for explain.c to inspect even though a hash table may have
been built in other processes.  This could happen either because
parallel_leader_participation was set to off or because the leader
happened to hit the end of the outer relation immediately (even though
the complete relation is not empty) and decided not to build the hash
table.

Commit bf11e7ee introduced a way for workers to exchange
instrumentation via the DSM segment for Sort nodes even though they
are not parallel-aware.  This commit does the same for Hash nodes, so
that explain.c has a way to find instrumentation data from an
arbitrary participant that actually built the hash table.

Author: Thomas Munro
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/CAEepm%3D3DUQC2-z252N55eOcZBer6DPdM%3DFzrxH9dZc5vYLsjaA%40mail.gmail.com
This commit is contained in:
Andres Freund
2017-12-05 10:55:56 -08:00
parent 82c5c533d1
commit 5bcf389ecf
8 changed files with 246 additions and 27 deletions
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9
src/include/executor/nodeHash.h
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@ -14,6 +14,7 @@
#ifndef NODEHASH_H
#define NODEHASH_H
#include "access/parallel.h"
#include "nodes/execnodes.h"
extern HashState *ExecInitHash(Hash *node, EState *estate, int eflags);
@ -48,5 +49,13 @@ extern void ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
int *numbatches,
int *num_skew_mcvs);
extern int ExecHashGetSkewBucket(HashJoinTable hashtable, uint32 hashvalue);
extern void ExecHashEstimate(HashState *node, ParallelContext *pcxt);
extern void ExecHashInitializeDSM(HashState *node, ParallelContext *pcxt);
extern void ExecHashInitializeWorker(HashState *node, ParallelWorkerContext *pwcxt);
extern void ExecHashReInitializeDSM(HashState *node, ParallelContext *pcxt);
extern void ExecHashRetrieveInstrumentation(HashState *node);
extern void ExecShutdownHash(HashState *node);
extern void ExecHashGetInstrumentation(HashInstrumentation *instrument,
HashJoinTable hashtable);
#endif /* NODEHASH_H */