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Restore sane locking behavior during parallel query.

Commit 9a3cebeaa changed things so that parallel workers didn't obtain
any lock of their own on tables they access.  That was clearly a bad
idea, but I'd mistakenly supposed that it was the intended end result
of the series of patches for simplifying the executor's lock management.
Undo that change in relation_open(), and adjust ExecOpenScanRelation()
so that it gets the correct lock if inside a parallel worker.

In passing, clean up some more obsolete comments about when locks
are acquired.

Discussion: https://postgr.es/m/468c85d9-540e-66a2-1dde-fec2b741e688@lab.ntt.co.jp
This commit is contained in:
Tom Lane
2018-10-06 15:49:37 -04:00
parent f2343653f5
commit 29ef2b310d
11 changed files with 34 additions and 34 deletions

View File

@ -732,16 +732,30 @@ ExecGetRangeTableRelation(EState *estate, Index rti)
Assert(rte->rtekind == RTE_RELATION);
rel = estate->es_relations[rti - 1] = heap_open(rte->relid, NoLock);
if (!IsParallelWorker())
{
/*
* In a normal query, we should already have the appropriate lock,
* but verify that through an Assert. Since there's already an
* Assert inside heap_open that insists on holding some lock, it
* seems sufficient to check this only when rellockmode is higher
* than the minimum.
*/
rel = heap_open(rte->relid, NoLock);
Assert(rte->rellockmode == AccessShareLock ||
CheckRelationLockedByMe(rel, rte->rellockmode, false));
}
else
{
/*
* If we are a parallel worker, we need to obtain our own local
* lock on the relation. This ensures sane behavior in case the
* parent process exits before we do.
*/
rel = heap_open(rte->relid, rte->rellockmode);
}
/*
* Verify that appropriate lock was obtained before execution.
*
* In the case of parallel query, only the leader would've obtained
* the lock (that needs to be fixed, though).
*/
Assert(IsParallelWorker() ||
CheckRelationLockedByMe(rel, rte->rellockmode, false));
estate->es_relations[rti - 1] = rel;
}
return rel;