Lock table in DROP STATISTICS

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
index 409cf28a7ef12fba96f1c8114454f3d671eb832b..dcdc5f85cdad3986ccac1f6afb98645367dc803f 100644 (file)
--- 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);
 }