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Previously, the SERIALIZABLE isolation level prevented parallel query
from being used. Allow the two features to be used together by
sharing the leader's SERIALIZABLEXACT with parallel workers.
An extra per-SERIALIZABLEXACT LWLock is introduced to make it safe to
share, and new logic is introduced to coordinate the early release
of the SERIALIZABLEXACT required for the SXACT_FLAG_RO_SAFE
optimization, as follows:
The first backend to observe the SXACT_FLAG_RO_SAFE flag (set by
some other transaction) will 'partially release' the SERIALIZABLEXACT,
meaning that the conflicts and locks it holds are released, but the
SERIALIZABLEXACT itself will remain active because other backends
might still have a pointer to it.
Whenever any backend notices the SXACT_FLAG_RO_SAFE flag, it clears
its own MySerializableXact variable and frees local resources so that
it can skip SSI checks for the rest of the transaction. In the
special case of the leader process, it transfers the SERIALIZABLEXACT
to a new variable SavedSerializableXact, so that it can be completely
released at the end of the transaction after all workers have exited.
Remove the serializable_okay flag added to CreateParallelContext() by
commit 9da0cc35, because it's now redundant.
Author: Thomas Munro
Reviewed-by: Haribabu Kommi, Robert Haas, Masahiko Sawada, Kevin Grittner
Discussion: https://postgr.es/m/CAEepm=0gXGYhtrVDWOTHS8SQQy_=S9xo+8oCxGLWZAOoeJ=yzQ@mail.gmail.com
87 lines
3.0 KiB
C
87 lines
3.0 KiB
C
/*-------------------------------------------------------------------------
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*
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* predicate.h
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* POSTGRES public predicate locking definitions.
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*
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/predicate.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PREDICATE_H
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#define PREDICATE_H
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#include "storage/lock.h"
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#include "utils/relcache.h"
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#include "utils/snapshot.h"
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/*
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* GUC variables
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*/
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extern int max_predicate_locks_per_xact;
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extern int max_predicate_locks_per_relation;
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extern int max_predicate_locks_per_page;
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/* Number of SLRU buffers to use for predicate locking */
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#define NUM_OLDSERXID_BUFFERS 16
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/*
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* A handle used for sharing SERIALIZABLEXACT objects between the participants
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* in a parallel query.
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*/
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typedef void *SerializableXactHandle;
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/*
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* function prototypes
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*/
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/* housekeeping for shared memory predicate lock structures */
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extern void InitPredicateLocks(void);
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extern Size PredicateLockShmemSize(void);
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extern void CheckPointPredicate(void);
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/* predicate lock reporting */
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extern bool PageIsPredicateLocked(Relation relation, BlockNumber blkno);
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/* predicate lock maintenance */
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extern Snapshot GetSerializableTransactionSnapshot(Snapshot snapshot);
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extern void SetSerializableTransactionSnapshot(Snapshot snapshot,
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VirtualTransactionId *sourcevxid,
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int sourcepid);
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extern void RegisterPredicateLockingXid(TransactionId xid);
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extern void PredicateLockRelation(Relation relation, Snapshot snapshot);
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extern void PredicateLockPage(Relation relation, BlockNumber blkno, Snapshot snapshot);
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extern void PredicateLockTuple(Relation relation, HeapTuple tuple, Snapshot snapshot);
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extern void PredicateLockPageSplit(Relation relation, BlockNumber oldblkno, BlockNumber newblkno);
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extern void PredicateLockPageCombine(Relation relation, BlockNumber oldblkno, BlockNumber newblkno);
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extern void TransferPredicateLocksToHeapRelation(Relation relation);
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extern void ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe);
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/* conflict detection (may also trigger rollback) */
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extern void CheckForSerializableConflictOut(bool valid, Relation relation, HeapTuple tuple,
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Buffer buffer, Snapshot snapshot);
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extern void CheckForSerializableConflictIn(Relation relation, HeapTuple tuple, Buffer buffer);
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extern void CheckTableForSerializableConflictIn(Relation relation);
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/* final rollback checking */
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extern void PreCommit_CheckForSerializationFailure(void);
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/* two-phase commit support */
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extern void AtPrepare_PredicateLocks(void);
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extern void PostPrepare_PredicateLocks(TransactionId xid);
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extern void PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit);
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extern void predicatelock_twophase_recover(TransactionId xid, uint16 info,
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void *recdata, uint32 len);
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/* parallel query support */
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extern SerializableXactHandle ShareSerializableXact(void);
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extern void AttachSerializableXact(SerializableXactHandle handle);
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#endif /* PREDICATE_H */
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