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Handle lack of DSM slots in parallel btree build, take 2.

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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
This commit is contained in:
Thomas Munro 2020-02-05 12:21:03 +13:00
parent 7d91b604d9
commit d9fe702a2c
1 changed files with 10 additions and 8 deletions
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18
src/backend/access/nbtree/nbtsort.c
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@ -1332,14 +1332,6 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
pcxt = CreateParallelContext("postgres", "_bt_parallel_build_main",
request);
/* If no DSM segment was available, back out (do serial build) */
if (pcxt->seg == NULL)
{
DestroyParallelContext(pcxt);
ExitParallelMode();
return;
}
scantuplesortstates = leaderparticipates ? request + 1 : request;
/*
@ -1383,6 +1375,16 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
/* Everyone's had a chance to ask for space, so now create the DSM */
InitializeParallelDSM(pcxt);
/* If no DSM segment was available, back out (do serial build) */
if (pcxt->seg == NULL)
{
if (IsMVCCSnapshot(snapshot))
UnregisterSnapshot(snapshot);
DestroyParallelContext(pcxt);
ExitParallelMode();
return;
}
/* Store shared build state, for which we reserved space */
btshared = (BTShared *) shm_toc_allocate(pcxt->toc, estbtshared);
/* Initialize immutable state */