Avoid crashing when a table is deleted while we're on the process of checking

it.  This is a stripped down version of the patch applied to HEAD.

Per report from Tom Lane based on buildfarm evidence.

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index bd2d2731399b77e89bf5fee0f4db877b09753861..d8602c6641ec521a6a4d3292e4aaeb5a8d05ab86 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2098,13 +2098,16 @@ do_autovacuum(void)
 
                /*
                 * Save the relation name for a possible error message, to avoid a
-                * catalog lookup in case of an error.  Note: they must live in a
-                * long-lived memory context because we call vacuum and analyze in
-                * different transactions.
+                * catalog lookup in case of an error.  If any of these return NULL,
+                * then the relation has been dropped since last we checked; skip it.
+                * Note: they must live in a long-lived memory context because we call
+                * vacuum and analyze in different transactions.
                 */
                datname = get_database_name(MyDatabaseId);
                nspname = get_namespace_name(get_rel_namespace(tab->at_relid));
                relname = get_rel_name(tab->at_relid);
+               if (!datname || !nspname || !relname)
+                       goto deleted;
 
                /*
                 * We will abort vacuuming the current table if something errors out,
@@ -2158,11 +2161,15 @@ do_autovacuum(void)
 
                /* the PGPROC flags are reset at the next end of transaction */
 
+deleted:
                /* be tidy */
                pfree(tab);
-               pfree(datname);
-               pfree(nspname);
-               pfree(relname);
+               if (datname)
+                       pfree(datname);
+               if (nspname)
+                       pfree(nspname);
+               if (relname)
+                       pfree(relname);
 
                /* remove my info from shared memory */
                LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);