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commit    bb7628e55eda6f450f0f824d11c9a34b11f6bb12
Author:   Tomas Vondra <tomas.vondra@postgresql.org>
Date:     Mon Sep 20 23:14:11 2021 +0000

    Free memory after building each statistics object
    
    Until now, all extended statistics on a given relation were built in the
    same memory context, without resetting. Some of the memory was released
    explicitly, but not all of it - for example memory allocated while
    detoasting values is hard to free. This is how it worked since extended
    statistics were introduced in PostgreSQL 10, but adding support for
    extended stats on expressions made the issue somewhat worse as it
    increases the number of statistics to build.
    
    Fixed by adding a memory context which gets reset after building each
    statistics object (all the statistics kinds included in it). Resetting
    it after building each statistics kind would be even better, but it
    would require more invasive changes and copying of results, making it
    harder to backpatch.
    
    Backpatch to PostgreSQL 10, where extended statistics were introduced.
    
    Author: Justin Pryzby
    Reported-by: Justin Pryzby
    Reviewed-by: Tomas Vondra
    Backpatch-through: 10
    Discussion: https://www.postgresql.org/message-id/20210915200928.GP831%40telsasoft.com


 src/backend/statistics/extended_stats.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c
index 2e55913bc8f..5fa36e0036e 100644
--- a/src/backend/statistics/extended_stats.c
+++ b/src/backend/statistics/extended_stats.c
@@ -125,14 +125,16 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
 	if (!natts)
 		return;
 
+	/* the list of stats has to be allocated outside the memory context */
+	pg_stext = table_open(StatisticExtRelationId, RowExclusiveLock);
+	statslist = fetch_statentries_for_relation(pg_stext, RelationGetRelid(onerel));
+
+	/* memory context for building each statistics object */
 	cxt = AllocSetContextCreate(CurrentMemoryContext,
 								"BuildRelationExtStatistics",
 								ALLOCSET_DEFAULT_SIZES);
 	oldcxt = MemoryContextSwitchTo(cxt);
 
-	pg_stext = table_open(StatisticExtRelationId, RowExclusiveLock);
-	statslist = fetch_statentries_for_relation(pg_stext, RelationGetRelid(onerel));
-
 	/* report this phase */
 	if (statslist != NIL)
 	{
@@ -234,14 +236,16 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
 		pgstat_progress_update_param(PROGRESS_ANALYZE_EXT_STATS_COMPUTED,
 									 ++ext_cnt);
 
-		/* free the build data (allocated as a single chunk) */
-		pfree(data);
+		/* free the data used for building this statistics object */
+		MemoryContextReset(cxt);
 	}
 
-	table_close(pg_stext, RowExclusiveLock);
-
 	MemoryContextSwitchTo(oldcxt);
 	MemoryContextDelete(cxt);
+
+	list_free(statslist);
+
+	table_close(pg_stext, RowExclusiveLock);
 }
 
 /*


[parent: 9eff85932659]