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Handle lack of DSM slots in parallel btree build.

author Thomas Munro <tmunro@postgresql.org>

2020年1月30日 21:25:34 +0000 (10:25 +1300)

committer Thomas Munro <tmunro@postgresql.org>

2020年1月30日 22:12:21 +0000 (11:12 +1300)

If no DSM slots are available, a ParallelContext can still be
created, but its seg pointer is NULL. Teach parallel btree build
to cope with that by falling back to a regular non-parallel build,
to avoid crashing with a segmentation fault.

Back-patch to 11, where parallel CREATE INDEX landed.

Reported-by: Nicola Contu
Reviewed-by: Peter Geoghegan
Discussion: https://postgr.es/m/CA%2BhUKGJgJEBnkuODBVomyK3MWFvDBbMVj%3Dgdt6DnRPU-5sQ6UQ%40mail.gmail.com

src/backend/access/nbtree/nbtsort.c patch | blob | blame | history

diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c

index 16f57557776908519ea376f8ea2a5803acc50131..bc00799b964b91437ef932bd3ddd6c9c781e9283 100644 (file)

--- a/src/backend/access/nbtree/nbtsort.c

+++ b/src/backend/access/nbtree/nbtsort.c

@@ -1256,6 +1256,15 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)

Assert(request > 0);

pcxt = CreateParallelContext("postgres", "_bt_parallel_build_main",

request, true);

+ /* If no DSM segment was available, back out (do serial build) */

+ if (pcxt->seg == NULL)

+ {

+ DestroyParallelContext(pcxt);

+ ExitParallelMode();

+ return;

+ }

scantuplesortstates = leaderparticipates ? request + 1 : request;

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