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Fix logic in lazy vacuum to decide if it's worth trying to truncate the heap.

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If the table was smaller than REL_TRUNCATE_FRACTION (= 16) pages, we always
tried to acquire AccessExclusiveLock on it even if there was no empty pages
at the end.

Report by Simon Riggs. Back-patch all the way to 7.4.
This commit is contained in:
Heikki Linnakangas
2009-01-06 14:55:56 +00:00
parent b27de223da
commit fcd3890f3c
1 changed files with 4 additions and 3 deletions
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7
src/backend/commands/vacuumlazy.c
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@ -33,7 +33,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.61.2.6 2007/09/24 03:53:06 alvherre Exp $ * $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.61.2.7 2009/01/06 14:55:56 heikki Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -175,8 +175,9 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
* number of pages. Otherwise, the time taken isn't worth it. * number of pages. Otherwise, the time taken isn't worth it.
*/ */
possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages; possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages;
if (possibly_freeable >= REL_TRUNCATE_MINIMUM || if (possibly_freeable > 0 &&
possibly_freeable >= vacrelstats->rel_pages / REL_TRUNCATE_FRACTION) (possibly_freeable >= REL_TRUNCATE_MINIMUM ||
possibly_freeable >= vacrelstats->rel_pages / REL_TRUNCATE_FRACTION))
lazy_truncate_heap(onerel, vacrelstats); lazy_truncate_heap(onerel, vacrelstats);
/* Update shared free space map with final free space info */ /* Update shared free space map with final free space info */