CREATE INDEX: don't update table stats if autovacuum=off.

We previously fixed this for binary upgrade in 71b6617, but a
similar problem remained when dumping statistics without data.

Fix by not opportunistically updating table stats during CREATE INDEX
when autovacuum is disabled. For stats to be stable at all, the server
needs to be aware that it should not take every opportunity to update
stats. Per discussion, autovacuum=off is a signal that the user
expects stats to be stable; though if necessary, we could create
a more specific mode in the future.

Reported-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Discussion: https://postgr.es/m/CAExHW5vf9D+8-a5_BEX3y=2y_xY9hiCxV1=C+FnxDvfprWvkng@mail.gmail.com
Discussion: https://postgr.es/m/ca81cbf6e6ea2af838df972801ad4da52640a503.camel%40j-davis.com

Author: jeff-davis

src/backend/catalog/index.c

@@ -63,6 +63,7 @@
 #include "optimizer/optimizer.h"
 #include "parser/parser.h"
 #include "pgstat.h"
+#include "postmaster/autovacuum.h"
 #include "rewrite/rewriteManip.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
@@ -2840,6 +2841,27 @@ index_update_stats(Relation rel,
 	 */
 	update_stats = reltuples >= 0 && !IsBinaryUpgrade;
 
+	/*
+	 * If autovacuum is off, user may not be expecting table relstats to
+	 * change.  This can be important when restoring a dump that includes
+	 * statistics, as the table statistics may be restored before the index is
+	 * created, and we want to preserve the restored table statistics.
+	 */
+	if (AutoVacuumingActive())
+	{
+		if (rel->rd_rel->relkind == RELKIND_RELATION ||
+			rel->rd_rel->relkind == RELKIND_TOASTVALUE ||
+			rel->rd_rel->relkind == RELKIND_MATVIEW)
+		{
+			StdRdOptions *options = (StdRdOptions *) rel->rd_options;
+
+			if (options != NULL && !options->autovacuum.enabled)
+				update_stats = false;
+		}
+	}
+	else
+		update_stats = false;
+
 	/*
 	 * Finish I/O and visibility map buffer locks before
 	 * systable_inplace_update_begin() locks the pg_class buffer.  The rd_rel

src/test/regress/expected/stats_import.out

@@ -12,7 +12,36 @@ CREATE TABLE stats_import.test(
     arange int4range,
     tags text[]
 ) WITH (autovacuum_enabled = false);
+SELECT
+    pg_catalog.pg_restore_relation_stats(
+        'relation', 'stats_import.test'::regclass,
+        'relpages', 18::integer,
+        'reltuples', 21::real,
+        'relallvisible', 24::integer,
+	'relallfrozen', 27::integer);
+ pg_restore_relation_stats 
+---------------------------
+ t
+(1 row)
+
+-- CREATE INDEX on a table with autovac disabled should not overwrite
+-- stats
 CREATE INDEX test_i ON stats_import.test(id);
+SELECT relname, relpages, reltuples, relallvisible, relallfrozen
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass
+ORDER BY relname;
+ relname | relpages | reltuples | relallvisible | relallfrozen 
+---------+----------+-----------+---------------+--------------
+ test    |       18 |        21 |            24 |           27
+(1 row)
+
+SELECT pg_clear_relation_stats('stats_import.test'::regclass);
+ pg_clear_relation_stats 
+-------------------------
+ 
+(1 row)
+
 --
 -- relstats tests
 --

src/test/regress/sql/stats_import.sql

@@ -15,8 +15,25 @@ CREATE TABLE stats_import.test(
     tags text[]
 ) WITH (autovacuum_enabled = false);
 
+SELECT
+    pg_catalog.pg_restore_relation_stats(
+        'relation', 'stats_import.test'::regclass,
+        'relpages', 18::integer,
+        'reltuples', 21::real,
+        'relallvisible', 24::integer,
+	'relallfrozen', 27::integer);
+
+-- CREATE INDEX on a table with autovac disabled should not overwrite
+-- stats
 CREATE INDEX test_i ON stats_import.test(id);
 
+SELECT relname, relpages, reltuples, relallvisible, relallfrozen
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass
+ORDER BY relname;
+
+SELECT pg_clear_relation_stats('stats_import.test'::regclass);
+
 --
 -- relstats tests
 --