Explain dropdb can't use syscache because of TOAST

tvondra · tvondra · commit e498d22e2135 · 2024-08-19T14:00:50.000+02:00
Add a comment explaining dropdb() can't rely on syscache. The issue with flattened rows was fixed by commit 0f92b23, but better to have a clear explanation why the systable scan is necessary. The other places doing in-place updates on pg_database have the same comment. Suggestion and patch by Yugo Nagata. Backpatch to 12, same as the fix. Author: Yugo Nagata Backpatch-through: 12 Discussion: https://postgr.es/m/CAJTYsWWNkCt+-UnMhg=BiCD3Mh8c2JdHLofPxsW3m2dkDFw8RA@mail.gmail.com
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
@@ -1663,7 +1663,9 @@ dropdb(const char *dbname, bool missing_ok, bool force)
 	pgstat_drop_database(db_id);
 
 	/*
-	 * Update the database's pg_database tuple
+	 * Get the pg_database tuple to scribble on.  Note that this does not
+	 * directly rely on the syscache to avoid issues with flattened toast
+	 * values for the in-place update.
 	 */
 	ScanKeyInit(&scankey,
 				Anum_pg_database_datname,
