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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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30
src/backend/commands/vacuumlazy.c
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@ -29,7 +29,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.119 2009/03/24 20:17:14 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.120 2009/06/06 22:13:51 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -84,9 +84,11 @@ typedef struct LVRelStats
{
/* hasindex = true means two-pass strategy; false means one-pass */
bool hasindex;
bool scanned_all; /* have we scanned all pages (this far)? */
/* Overall statistics about rel */
BlockNumber rel_pages;
double rel_tuples;
double old_rel_tuples; /* previous value of pg_class.reltuples */
double rel_tuples; /* counts only tuples on scanned pages */
BlockNumber pages_removed;
double tuples_deleted;
BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */
@ -96,7 +98,6 @@ typedef struct LVRelStats
int max_dead_tuples; /* # slots allocated in array */
ItemPointer dead_tuples; /* array of ItemPointerData */
int num_index_scans;
bool scanned_all; /* have we scanned all pages (this far)? */
} LVRelStats;
@ -174,8 +175,9 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));
vacrelstats->num_index_scans = 0;
vacrelstats->scanned_all = true; /* will be cleared if we skip a page */
vacrelstats->old_rel_tuples = onerel->rd_rel->reltuples;
vacrelstats->num_index_scans = 0;
/* Open all indexes of the relation */
vac_open_indexes(onerel, RowExclusiveLock, &nindexes, &Irel);
@ -876,9 +878,9 @@ lazy_vacuum_index(Relation indrel,
ivinfo.index = indrel;
ivinfo.vacuum_full = false;
ivinfo.analyze_only = false;
ivinfo.estimated_count = true;
ivinfo.message_level = elevel;
/* We don't yet know rel_tuples, so pass -1 */
ivinfo.num_heap_tuples = -1;
ivinfo.num_heap_tuples = vacrelstats->old_rel_tuples;
ivinfo.strategy = vac_strategy;
/* Do bulk deletion */
@ -908,8 +910,10 @@ lazy_cleanup_index(Relation indrel,
ivinfo.index = indrel;
ivinfo.vacuum_full = false;
ivinfo.analyze_only = false;
ivinfo.estimated_count = !vacrelstats->scanned_all;
ivinfo.message_level = elevel;
ivinfo.num_heap_tuples = vacrelstats->rel_tuples;
/* use rel_tuples only if we scanned all pages, else fall back */
ivinfo.num_heap_tuples = vacrelstats->scanned_all ? vacrelstats->rel_tuples : vacrelstats->old_rel_tuples;
ivinfo.strategy = vac_strategy;
stats = index_vacuum_cleanup(&ivinfo, stats);
@ -917,10 +921,14 @@ lazy_cleanup_index(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",