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Commitb564eb0

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Free memory after building each statistics object
Until now, all extended statistics on a given relation were built in thesame memory context, without resetting. Some of the memory was releasedexplicitly, but not all of it - for example memory allocated whiledetoasting values is hard to free. This is how it worked since extendedstatistics were introduced in PostgreSQL 10, but adding support forextended stats on expressions made the issue somewhat worse as itincreases the number of statistics to build.Fixed by adding a memory context which gets reset after building eachstatistics object (all the statistics kinds included in it). Resettingit after building each statistics kind would be even better, but itwould require more invasive changes and copying of results, making itharder to backpatch.Backpatch to PostgreSQL 10, where extended statistics were introduced.Author: Justin PryzbyReported-by: Justin PryzbyReviewed-by: Tomas VondraBackpatch-through: 10Discussion:https://www.postgresql.org/message-id/20210915200928.GP831%40telsasoft.com
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‎src/backend/statistics/extended_stats.c

Lines changed: 11 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -97,14 +97,15 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
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MemoryContextoldcxt;
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int64ext_cnt;
9999

100+
pg_stext=table_open(StatisticExtRelationId,RowExclusiveLock);
101+
stats=fetch_statentries_for_relation(pg_stext,RelationGetRelid(onerel));
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103+
/* memory context for building each statistics object */
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cxt=AllocSetContextCreate(CurrentMemoryContext,
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"BuildRelationExtStatistics",
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ALLOCSET_DEFAULT_SIZES);
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oldcxt=MemoryContextSwitchTo(cxt);
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105-
pg_stext=table_open(StatisticExtRelationId,RowExclusiveLock);
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stats=fetch_statentries_for_relation(pg_stext,RelationGetRelid(onerel));
107-
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/* report this phase */
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if (stats!=NIL)
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{
@@ -189,12 +190,17 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
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/* for reporting progress */
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pgstat_progress_update_param(PROGRESS_ANALYZE_EXT_STATS_COMPUTED,
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++ext_cnt);
192-
}
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194-
table_close(pg_stext,RowExclusiveLock);
194+
/* free the data used for building this statistics object */
195+
MemoryContextReset(cxt);
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}
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MemoryContextSwitchTo(oldcxt);
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MemoryContextDelete(cxt);
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list_free(stats);
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table_close(pg_stext,RowExclusiveLock);
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}
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/*

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