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Improve the IndexVacuumInfo/IndexBulkDeleteResult API to allow somewhat sane

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behavior in cases where we don't know the heap tuple count accurately; in
particular partial vacuum, but this also makes the API a bit more useful
for ANALYZE.  This patch adds "estimated_count" flags to both structs so
that an approximate count can be flagged as such, and adjusts the logic
so that approximate counts are not used for updating pg_class.reltuples.

This fixes my previous complaint that VACUUM was putting ridiculous values
into pg_class.reltuples for indexes.  The actual impact of that bug is
limited, because the planner only pays attention to reltuples for an index
if the index is partial; which probably explains why beta testers hadn't
noticed a degradation in plan quality from it.  But it needs to be fixed.

The whole thing is a bit messy and should be redesigned in future, because
reltuples now has the potential to drift quite far away from reality when
a long period elapses with no non-partial vacuums.  But this is as good as
it's going to get for 8.4.
This commit is contained in:
Tom Lane
2009-06-06 22:13:52 +00:00
parent 4334695b30
commit 32ea236361
10 changed files with 81 additions and 39 deletions
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10
src/backend/access/nbtree/nbtree.c
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@ -12,7 +12,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.169 2009/05/05 19:36:32 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.170 2009/06/06 22:13:51 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -579,10 +579,11 @@ btvacuumcleanup(PG_FUNCTION_ARGS)
/*
* During a non-FULL vacuum it's quite possible for us to be fooled by
* concurrent page splits into double-counting some index tuples, so
* disbelieve any total that exceeds the underlying heap's count. (We
* can't check this during btbulkdelete.)
* disbelieve any total that exceeds the underlying heap's count ...
* if we know that accurately. Otherwise this might just make matters
* worse.
*/
if (!info->vacuum_full)
if (!info->vacuum_full && !info->estimated_count)
{
if (stats->num_index_tuples > info->num_heap_tuples)
stats->num_index_tuples = info->num_heap_tuples;
@ -618,6 +619,7 @@ btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
* Reset counts that will be incremented during the scan; needed in case
* of multiple scans during a single VACUUM command
*/
stats->estimated_count = false;
stats->num_index_tuples = 0;
stats->pages_deleted = 0;