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Fix ReinitializeParallelDSM to tolerate finding no error queues. 

Commit d466335064 changed things so
that shm_toc_lookup would fail with an error rather than silently
returning NULL in the hope that such failures would be reported
in a useful way rather than via a system crash.  However, it
overlooked the fact that the lookup of PARALLEL_KEY_ERROR_QUEUE
in ReinitializeParallelDSM is expected to fail when no DSM segment
was created in the first place; in that case, we end up with a
backend-private memory segment that still contains an entry for
PARALLEL_KEY_FIXED but no others.  Consequently a benign failure
to initialize parallelism can escalate into an elog(ERROR);
repair.

Discussion: http://postgr.es/m/CA+Tgmob8LFw55DzH1QEREpBEA9RJ_W_amhBFCVZ6WMwUhVpOqg@mail.gmail.com
This commit is contained in:
Robert Haas 2017-11-28 12:05:52 -05:00
parent c6755e233b
commit 445dbd82a3
1 changed files with 3 additions and 2 deletions
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5
src/backend/access/transam/parallel.c
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@ -428,9 +428,10 @@ ReinitializeParallelDSM(ParallelContext *pcxt)
fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
fps->last_xlog_end = 0;
/* Recreate error queues. */
/* Recreate error queues (if they exist). */
error_queue_space =
shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, false);
shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, true);
Assert(pcxt->nworkers == 0 || error_queue_space != NULL);
for (i = 0; i < pcxt->nworkers; ++i)
{
char *start;