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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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34
src/backend/commands/vacuum.c
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@@ -13,7 +13,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.387 2009/03/31 22:12:48 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.388 2009/06/06 22:13:51 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -3389,6 +3389,7 @@ scan_index(Relation indrel, double num_tuples)
ivinfo.index = indrel;
ivinfo.vacuum_full = true;
ivinfo.analyze_only = false;
ivinfo.estimated_count = false;
ivinfo.message_level = elevel;
ivinfo.num_heap_tuples = num_tuples;
ivinfo.strategy = vac_strategy;
@@ -3398,10 +3399,14 @@ scan_index(Relation indrel, double num_tuples)
if (!stats)
return;
/* now update statistics in pg_class */
vac_update_relstats(indrel,
stats->num_pages, stats->num_index_tuples,
false, InvalidTransactionId);
/*
* Now update statistics in pg_class, but only if the index says the
* count is accurate.
*/
if (!stats->estimated_count)
vac_update_relstats(indrel,
stats->num_pages, stats->num_index_tuples,
false, InvalidTransactionId);
ereport(elevel,
(errmsg("index \"%s\" now contains %.0f row versions in %u pages",
@@ -3417,7 +3422,8 @@ scan_index(Relation indrel, double num_tuples)
* Check for tuple count mismatch. If the index is partial, then it's OK
* for it to have fewer tuples than the heap; else we got trouble.
*/
if (stats->num_index_tuples != num_tuples)
if (!stats->estimated_count &&
stats->num_index_tuples != num_tuples)
{
if (stats->num_index_tuples > num_tuples ||
!vac_is_partial_index(indrel))
@@ -3456,6 +3462,7 @@ vacuum_index(VacPageList vacpagelist, Relation indrel,
ivinfo.index = indrel;
ivinfo.vacuum_full = true;
ivinfo.analyze_only = false;
ivinfo.estimated_count = false;
ivinfo.message_level = elevel;
ivinfo.num_heap_tuples = num_tuples + keep_tuples;
ivinfo.strategy = vac_strategy;
@@ -3469,10 +3476,14 @@ vacuum_index(VacPageList vacpagelist, Relation indrel,
if (!stats)
return;
/* now update statistics in pg_class */
vac_update_relstats(indrel,
stats->num_pages, stats->num_index_tuples,
false, InvalidTransactionId);
/*
* Now update statistics in pg_class, but only if the index says the
* count is accurate.
*/
if (!stats->estimated_count)
vac_update_relstats(indrel,
stats->num_pages, stats->num_index_tuples,
false, InvalidTransactionId);
ereport(elevel,
(errmsg("index \"%s\" now contains %.0f row versions in %u pages",
@@ -3490,7 +3501,8 @@ vacuum_index(VacPageList vacpagelist, Relation indrel,
* Check for tuple count mismatch. If the index is partial, then it's OK
* for it to have fewer tuples than the heap; else we got trouble.
*/
if (stats->num_index_tuples != num_tuples + keep_tuples)
if (!stats->estimated_count &&
stats->num_index_tuples != num_tuples + keep_tuples)
{
if (stats->num_index_tuples > num_tuples + keep_tuples ||
!vac_is_partial_index(indrel))