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Repair VACUUM FULL bug introduced by HOT patch: the original way of

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calculating a page's initial free space was fine, and should not have been
"improved" by letting PageGetHeapFreeSpace do it.  VACUUM FULL is going to
reclaim LP_DEAD line pointers later, so there is no need for a guard
against the page being too full of line pointers, and having one risks
rejecting pages that are perfectly good move destinations.

This also exposed a second bug, which is that the empty_end_pages logic
assumed that any page with no live tuples would get entered into the
fraged_pages list automatically (by virtue of having more free space than
the threshold in the do_frag calculation).  This assumption certainly
seems risky when a low fillfactor has been chosen, and even without
tunable fillfactor I think it could conceivably fail on a page with many
unused line pointers.  So fix the code to force do_frag true when notup
is true, and patch this part of the fix all the way back.

Per report from Tomas Szepe.
This commit is contained in:
Tom Lane 2008-02-11 19:14:38 +00:00
parent f6693948c4
commit 4722e1f33c
1 changed files with 13 additions and 6 deletions
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19
src/backend/commands/vacuum.c
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@ -13,7 +13,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.342.2.4 2008/01/03 21:23:45 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.342.2.5 2008/02/11 19:14:38 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1521,12 +1521,18 @@ scan_heap(VRelStats *vacrelstats, Relation onerel,
free_space += vacpage->free;
/*
* Add the page to fraged_pages if it has a useful amount of free
* space. "Useful" means enough for a minimal-sized tuple. But we
* don't know that accurately near the start of the relation, so add
* pages unconditionally if they have >= BLCKSZ/10 free space.
* Add the page to vacuum_pages if it requires reaping, and add it to
* fraged_pages if it has a useful amount of free space. "Useful"
* means enough for a minimal-sized tuple. But we don't know that
* accurately near the start of the relation, so add pages
* unconditionally if they have >= BLCKSZ/10 free space. Also
* forcibly add pages with no live tuples, to avoid confusing the
* empty_end_pages logic. (In the presence of unreasonably small
* fillfactor, it seems possible that such pages might not pass
* the free-space test, but they had better be in the list anyway.)
*/
do_frag = (vacpage->free >= min_tlen || vacpage->free >= BLCKSZ / 10);
do_frag = (vacpage->free >= min_tlen || vacpage->free >= BLCKSZ / 10 ||
notup);
if (do_reap || do_frag)
{
@ -1541,6 +1547,7 @@ scan_heap(VRelStats *vacrelstats, Relation onerel,
/*
* Include the page in empty_end_pages if it will be empty after
* vacuuming; this is to keep us from using it as a move destination.
* Note that such pages are guaranteed to be in fraged_pages.
*/
if (notup)
{