Handle lack of DSM slots in parallel btree build, take 2.
Commit 74618e77
added a new check intended to fix a bug, but put
it in the wrong place so that parallel btree build was always
disabled. Do the check after we've actually tried to create
a DSM segment. Back-patch to 11, like the earlier commit.
Reviewed-by: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-WzmDABkJzrNnvf%2BOULK-_A_j9gkYg_Dz-H62jzNv4eKQTw%40mail.gmail.com
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@ -1332,14 +1332,6 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
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pcxt = CreateParallelContext("postgres", "_bt_parallel_build_main",
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request);
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/* If no DSM segment was available, back out (do serial build) */
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if (pcxt->seg == NULL)
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{
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DestroyParallelContext(pcxt);
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ExitParallelMode();
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return;
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}
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scantuplesortstates = leaderparticipates ? request + 1 : request;
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/*
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@ -1383,6 +1375,16 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
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/* Everyone's had a chance to ask for space, so now create the DSM */
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InitializeParallelDSM(pcxt);
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/* If no DSM segment was available, back out (do serial build) */
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if (pcxt->seg == NULL)
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{
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if (IsMVCCSnapshot(snapshot))
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UnregisterSnapshot(snapshot);
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DestroyParallelContext(pcxt);
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ExitParallelMode();
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return;
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}
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/* Store shared build state, for which we reserved space */
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btshared = (BTShared *) shm_toc_allocate(pcxt->toc, estbtshared);
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/* Initialize immutable state */
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