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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 14:55:50 +00:00
parent e4dcb11ead
commit 17409471b5
1 changed files with 4 additions and 3 deletions
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7
src/backend/commands/vacuumlazy.c
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@ -38,7 +38,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.81.2.4 2007/09/24 03:53:02 alvherre Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.81.2.5 2009/01/06 14:55:50 heikki Exp $
*
*-------------------------------------------------------------------------
*/
@ -181,8 +181,9 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
* number of pages. Otherwise, the time taken isn't worth it.
*/
possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages;
if (possibly_freeable >= REL_TRUNCATE_MINIMUM ||
possibly_freeable >= vacrelstats->rel_pages / REL_TRUNCATE_FRACTION)
if (possibly_freeable > 0 &&
(possibly_freeable >= REL_TRUNCATE_MINIMUM ||
possibly_freeable >= vacrelstats->rel_pages / REL_TRUNCATE_FRACTION))
lazy_truncate_heap(onerel, vacrelstats);
/* Update shared free space map with final free space info */