Lock table in DROP STATISTICS

tvondra · tvondra · commit 4f8d3c5b5ade · 2023-11-19T21:04:47.000+01:00
The DROP STATISTICS code failed to properly lock the table, leading to ERROR: tuple concurrently deleted when executed concurrently with ANALYZE. Fixed by modifying RemoveStatisticsById() to acquire the same lock as ANALYZE. This function is called only by DROP STATISTICS, as ANALYZE calls RemoveStatisticsDataById() directly. Reported by Justin Pryzby, fix by me. Backpatch through 12. The code was like this since it was introduced in 10, but older releases are EOL. Reported-by: Justin Pryzby Reviewed-by: Tom Lane Backpatch-through: 12 Discussion: https://postgr.es/m/ZUuk-8CfbYeq6g_u@pryzbyj2023
diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c
@@ -428,18 +428,12 @@ CreateStatistics(CreateStatsStmt *stmt)
 /*
  * Guts of statistics object deletion.
  */
-void
-RemoveStatisticsById(Oid statsOid)
+static void
+RemoveStatisticsDataById(Oid statsOid)
 {
 	Relation	relation;
 	HeapTuple	tup;
-	Form_pg_statistic_ext statext;
-	Oid			relid;
 
-	/*
-	 * First delete the pg_statistic_ext_data tuple holding the actual
-	 * statistical data.
-	 */
 	relation = table_open(StatisticExtDataRelationId, RowExclusiveLock);
 
 	tup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(statsOid));
@@ -452,6 +446,19 @@ RemoveStatisticsById(Oid statsOid)
 	ReleaseSysCache(tup);
 
 	table_close(relation, RowExclusiveLock);
+}
+
+/*
+ * Guts of statistics object deletion.
+ */
+void
+RemoveStatisticsById(Oid statsOid)
+{
+	Relation	relation;
+	Relation	rel;
+	HeapTuple	tup;
+	Form_pg_statistic_ext statext;
+	Oid			relid;
 
 	/*
 	 * Delete the pg_statistic_ext tuple.  Also send out a cache inval on the
@@ -467,12 +474,24 @@ RemoveStatisticsById(Oid statsOid)
 	statext = (Form_pg_statistic_ext) GETSTRUCT(tup);
 	relid = statext->stxrelid;
 
+	/*
+	 * Delete the pg_statistic_ext_data tuple holding the actual statistical
+	 * data. Lock the user table first, to prevent other processes (e.g. DROP
+	 * STATISTICS) from removing the row concurrently.
+	 */
+	rel = table_open(relid, ShareUpdateExclusiveLock);
+
+	RemoveStatisticsDataById(statsOid);
+
 	CacheInvalidateRelcacheByRelid(relid);
 
 	CatalogTupleDelete(relation, &tup->t_self);
 
 	ReleaseSysCache(tup);
 
+	/* Keep lock until the end of the transaction. */
+	table_close(rel, NoLock);
+
 	table_close(relation, RowExclusiveLock);
 }
 
