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| author | Thomas Munro <tmunro@postgresql.org> | 2019-08-28 13:37:03 +1200 |
|---|---|---|
| committer | Thomas Munro <tmunro@postgresql.org> | 2019-08-28 16:18:29 +1200 |
| commit | 720b59b55b84c8a346098cdbf3d34c7e554b0bf5 (patch) | |
| tree | 8b174c729c4752ef42ba8b4f1f366f1919fcfafd /src/include/utils/snapmgr.h | |
| parent | 80d0e5ba3fe03890831b425e85d10150e226239e (diff) | |
| download | postgresql-720b59b55b84c8a346098cdbf3d34c7e554b0bf5.tar.gz postgresql-720b59b55b84c8a346098cdbf3d34c7e554b0bf5.zip | |
Avoid catalog lookups in RelationAllowsEarlyPruning().
RelationAllowsEarlyPruning() performed a catalog scan, but is used
in two contexts where that was a bad idea:
1. In heap_page_prune_opt(), which runs very frequently in some large
scans. This caused major performance problems in a field report
that was easy to reproduce.
2. In TestForOldSnapshot(), which runs while we hold a buffer content
lock. It's not clear if this was guaranteed to be free of buffer
deadlock risk.
The check was introduced in commit 2cc41acd8 and defended against a
real problem: 9.6's hash indexes have no page LSN and so we can't
allow early pruning (ie the snapshot-too-old feature). We can remove
the check from all later releases though: hash indexes are now logged,
and there is no way to create UNLOGGED indexes on regular logged
tables.
If a future release allows such a combination, it might need to put
a similar check in place, but it'll need some more thought.
Back-patch to 10.
Author: Thomas Munro
Reviewed-by: Tom Lane, who spotted the second problem
Discussion: https://postgr.es/m/CA%2BhUKGKT8oTkp5jw_U4p0S-7UG9zsvtw_M47Y285bER6a2gD%2Bg%40mail.gmail.com
Discussion: https://postgr.es/m/CAA4eK1%2BWy%2BN4eE5zPm765h68LrkWc3Biu_8rzzi%2BOYX4j%2BiHRw%40mail.gmail.com
Diffstat (limited to 'src/include/utils/snapmgr.h')
| -rw-r--r-- | src/include/utils/snapmgr.h | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/src/include/utils/snapmgr.h b/src/include/utils/snapmgr.h index 8c070d7f412..67b07df48cb 100644 --- a/src/include/utils/snapmgr.h +++ b/src/include/utils/snapmgr.h @@ -40,7 +40,6 @@ RelationNeedsWAL(rel) \ && !IsCatalogRelation(rel) \ && !RelationIsAccessibleInLogicalDecoding(rel) \ - && !RelationHasUnloggedIndex(rel) \ ) #define EarlyPruningEnabled(rel) (old_snapshot_threshold >= 0 && RelationAllowsEarlyPruning(rel)) |