From c931c07124d4a582c7346942fa168e21e66a608f Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 11 Feb 2008 19:14:30 +0000
Subject: [PATCH] Repair VACUUM FULL bug introduced by HOT patch: the original
way of 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.
---
src/backend/commands/vacuum.c | 33 ++++++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 7 deletions(-)
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 6b2b70dd1a..20374f4cd6 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.363 2008/01/03 21:23:15 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.364 2008/02/11 19:14:30 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -1659,12 +1659,18 @@ 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)
{
@@ -1679,6 +1685,7 @@ 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)
{
@@ -3725,7 +3732,19 @@ enough_space(VacPage vacpage, Size len)
static Size
PageGetFreeSpaceWithFillFactor(Relation relation, Page page)
{
- Size freespace = PageGetHeapFreeSpace(page);
+ /*
+ * It is correct to use PageGetExactFreeSpace() here, *not*
+ * PageGetHeapFreeSpace(). This is because (a) we do our own, exact
+ * accounting for whether line pointers must be added, and (b) we will
+ * recycle any LP_DEAD line pointers before starting to add rows to a
+ * page, but that may not have happened yet at the time this function is
+ * applied to a page, which means PageGetHeapFreeSpace()'s protection
+ * against too many line pointers on a page could fire incorrectly. We do
+ * not need that protection here: since VACUUM FULL always recycles all
+ * dead line pointers first, it'd be physically impossible to insert more
+ * than MaxHeapTuplesPerPage tuples anyway.
+ */
+ Size freespace = PageGetExactFreeSpace(page);
Size targetfree;
targetfree = RelationGetTargetPageFreeSpace(relation,