Remove lazy_update_relstats; go back to having VACUUM just record the
actual number of unremoved tuples as pg_class.reltuples. The idea of trying to estimate a steady state condition still seems attractive, but this particular implementation crashed and burned ...
This commit is contained in:
Tom Lane
parent
adb1a6e95b
commit
73ed6d61bd
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@ -31,7 +31,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.51 2005/03/20 22:00:52 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.52 2005/03/25 22:51:31 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -107,10 +107,6 @@ static int lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
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static void lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats);
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static BlockNumber count_nondeletable_pages(Relation onerel,
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LVRelStats *vacrelstats);
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static void lazy_update_relstats(Relation rel, BlockNumber num_pages,
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BlockNumber pages_removed,
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double num_tuples, double tuples_removed,
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bool hasindex);
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static void lazy_space_alloc(LVRelStats *vacrelstats, BlockNumber relblocks);
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static void lazy_record_dead_tuple(LVRelStats *vacrelstats,
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ItemPointer itemptr);
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@ -180,10 +176,10 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
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lazy_update_fsm(onerel, vacrelstats);
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/* Update statistics in pg_class */
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lazy_update_relstats(onerel, vacrelstats->rel_pages,
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vacrelstats->pages_removed,
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vacrelstats->rel_tuples, vacrelstats->tuples_deleted,
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hasindex);
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vac_update_relstats(RelationGetRelid(onerel),
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vacrelstats->rel_pages,
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vacrelstats->rel_tuples,
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hasindex);
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}
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@ -622,9 +618,10 @@ lazy_scan_index(Relation indrel, LVRelStats *vacrelstats)
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return;
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/* now update statistics in pg_class */
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lazy_update_relstats(indrel, stats->num_pages, stats->pages_removed,
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stats->num_index_tuples, stats->tuples_removed,
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false);
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vac_update_relstats(RelationGetRelid(indrel),
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stats->num_pages,
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stats->num_index_tuples,
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false);
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ereport(elevel,
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(errmsg("index \"%s\" now contains %.0f row versions in %u pages",
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@ -697,9 +694,10 @@ lazy_vacuum_index(Relation indrel,
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*index_pages_removed += stats->pages_removed;
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/* now update statistics in pg_class */
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lazy_update_relstats(indrel, stats->num_pages, *index_pages_removed,
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stats->num_index_tuples, *index_tups_vacuumed,
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false);
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vac_update_relstats(RelationGetRelid(indrel),
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stats->num_pages,
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stats->num_index_tuples,
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false);
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ereport(elevel,
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(errmsg("index \"%s\" now contains %.0f row versions in %u pages",
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@ -922,51 +920,6 @@ count_nondeletable_pages(Relation onerel, LVRelStats *vacrelstats)
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return vacrelstats->nonempty_pages;
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}
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/*
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* lazy_update_relstats - update pg_class statistics for a table or index
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*
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* We always want to set relpages to an accurate value. However, for lazy
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* VACUUM it seems best to set reltuples to the average of the number of
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* rows before vacuuming and the number after vacuuming, rather than just
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* using the number after vacuuming. This will result in the best average
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* performance in a steady-state situation where VACUUMs are performed
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* regularly on a table of roughly constant size, assuming that the physical
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* number of pages in the table stays about the same throughout. (Note that
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* we do not apply the same logic to VACUUM FULL, because it repacks the table
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* and thereby boosts the tuple density.)
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*
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* An important point is that when the table size has decreased a lot during
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* vacuuming, the old reltuples count might give an overestimate of the tuple
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* density. We handle this by scaling down the old reltuples count by the
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* fraction by which the table has shortened before we merge it with the
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* new reltuples count. In particular this means that when relpages goes to
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* zero, reltuples will immediately go to zero as well, causing the planner
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* to fall back on other estimation procedures as the table grows again.
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*
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* Because we do this math independently for the table and the indexes, it's
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* quite possible to end up with an index's reltuples different from the
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* table's, which is silly except in the case of partial indexes. We don't
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* worry too much about that here; the planner contains filtering logic to
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* ensure it only uses sane estimates.
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*/
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static void
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lazy_update_relstats(Relation rel, BlockNumber num_pages,
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BlockNumber pages_removed,
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double num_tuples, double tuples_removed,
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bool hasindex)
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{
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double old_num_tuples;
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old_num_tuples = num_tuples + tuples_removed;
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if (pages_removed > 0)
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old_num_tuples *= (double) num_pages / (double) (num_pages + pages_removed);
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if (old_num_tuples > num_tuples)
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num_tuples = ceil((num_tuples + old_num_tuples) * 0.5);
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vac_update_relstats(RelationGetRelid(rel), num_pages, num_tuples,
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hasindex);
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}
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/*
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* lazy_space_alloc - space allocation decisions for lazy vacuum
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*
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