diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/commands/vacuum.c | 6 | ||||
| -rw-r--r-- | src/backend/commands/vacuumlazy.c | 40 | ||||
| -rw-r--r-- | src/backend/utils/cache/relcache.c | 4 |
3 files changed, 38 insertions, 12 deletions
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index 5decc5cac67..606e782ba98 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -485,8 +485,10 @@ vac_estimate_reltuples(Relation relation, bool is_analyze, return scanned_tuples; /* - * If scanned_pages is zero but total_pages isn't, keep the existing - * value of reltuples. + * If scanned_pages is zero but total_pages isn't, keep the existing value + * of reltuples. (Note: callers should avoid updating the pg_class + * statistics in this situation, since no new information has been + * provided.) */ if (scanned_pages == 0) return old_rel_tuples; diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c index 23c4d5a00b9..89de6693ae2 100644 --- a/src/backend/commands/vacuumlazy.c +++ b/src/backend/commands/vacuumlazy.c @@ -84,6 +84,7 @@ typedef struct LVRelStats /* hasindex = true means two-pass strategy; false means one-pass */ bool hasindex; /* Overall statistics about rel */ + BlockNumber old_rel_pages; /* previous value of pg_class.relpages */ BlockNumber rel_pages; /* total number of pages */ BlockNumber scanned_pages; /* number of pages we examined */ double scanned_tuples; /* counts only tuples on scanned pages */ @@ -154,6 +155,9 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt, TimestampTz starttime = 0; bool scan_all; TransactionId freezeTableLimit; + BlockNumber new_rel_pages; + double new_rel_tuples; + TransactionId new_frozen_xid; pg_rusage_init(&ru0); @@ -176,6 +180,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt, vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats)); + vacrelstats->old_rel_pages = onerel->rd_rel->relpages; vacrelstats->old_rel_tuples = onerel->rd_rel->reltuples; vacrelstats->num_index_scans = 0; @@ -205,20 +210,39 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt, FreeSpaceMapVacuum(onerel); /* - * Update statistics in pg_class. But don't change relfrozenxid if we - * skipped any pages. + * Update statistics in pg_class. + * + * A corner case here is that if we scanned no pages at all because every + * page is all-visible, we should not update relpages/reltuples, because + * we have no new information to contribute. In particular this keeps + * us from replacing relpages=reltuples=0 (which means "unknown tuple + * density") with nonzero relpages and reltuples=0 (which means "zero + * tuple density") unless there's some actual evidence for the latter. + * + * Also, don't change relfrozenxid if we skipped any pages, since then + * we don't know for certain that all tuples have a newer xmin. */ + new_rel_pages = vacrelstats->rel_pages; + new_rel_tuples = vacrelstats->new_rel_tuples; + if (vacrelstats->scanned_pages == 0 && new_rel_pages > 0) + { + new_rel_pages = vacrelstats->old_rel_pages; + new_rel_tuples = vacrelstats->old_rel_tuples; + } + + new_frozen_xid = FreezeLimit; + if (vacrelstats->scanned_pages < vacrelstats->rel_pages) + new_frozen_xid = InvalidTransactionId; + vac_update_relstats(onerel, - vacrelstats->rel_pages, vacrelstats->new_rel_tuples, + new_rel_pages, new_rel_tuples, vacrelstats->hasindex, - (vacrelstats->scanned_pages < vacrelstats->rel_pages) ? - InvalidTransactionId : - FreezeLimit); + new_frozen_xid); /* report results to the stats collector, too */ pgstat_report_vacuum(RelationGetRelid(onerel), onerel->rd_rel->relisshared, - vacrelstats->new_rel_tuples); + new_rel_tuples); /* and log the action if appropriate */ if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0) @@ -238,7 +262,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt, vacrelstats->pages_removed, vacrelstats->rel_pages, vacrelstats->tuples_deleted, - vacrelstats->new_rel_tuples, + new_rel_tuples, pg_rusage_show(&ru0)))); } } diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c index d72c64f737b..5e6158db25b 100644 --- a/src/backend/utils/cache/relcache.c +++ b/src/backend/utils/cache/relcache.c @@ -1454,8 +1454,8 @@ formrdesc(const char *relationName, Oid relationReltype, */ relation->rd_rel->relistemp = false; - relation->rd_rel->relpages = 1; - relation->rd_rel->reltuples = 1; + relation->rd_rel->relpages = 0; + relation->rd_rel->reltuples = 0; relation->rd_rel->relkind = RELKIND_RELATION; relation->rd_rel->relhasoids = hasoids; relation->rd_rel->relnatts = (int16) natts; |