patch for pg_autovacuum 8.0.x prevent segv for dropped tables

Apologies if this is old news, but pg_autovacuum in 8.0.x has the bad habit
of SEGVing and exiting when a table gets dropped out from under it. This
creates problems if you rely on pg_autovacuum for the bulk of your vacuuming
as it forgets it's statistics when it is restarted and so will skip some
desireable vacuums.

I looked at the new autovacuum in 8.1 and it appears from casual inspection
not to have the same problem.

Below is a patch for this that should apply against any 8.0.x. The change
verifies that the catalog query returned some rows before accessing the row
data.

-dg

diff -Naur source/postgresql-8.0.2/contrib/pg_autovacuum/pg_autovacuum.c
build/postgresql-8.0.2/contrib/pg_autovacuum/pg_autovacuum.c
--- source/postgresql-8.0.2/contrib/pg_autovacuum/pg_autovacuum.c    2005-04-02 16:02:03.000000000 -0800
+++ build/postgresql-8.0.2/contrib/pg_autovacuum/pg_autovacuum.c    2005-09-28 22:15:25.428710172 -0700
@@ -1013,6 +1013,7 @@
 static void
 perform_maintenance_command(db_info * dbi, tbl_info * tbl, int operation)
 {
+    PGresult    *res;
     char        buf[256];

     /*
@@ -1069,10 +1070,16 @@
         fflush(LOGOUTPUT);
     }

-    send_query(buf, dbi);
-
-    update_table_thresholds(dbi, tbl, operation);
-
+    res = send_query(buf, dbi);
+    if (PQntuples(res)) {
+        update_table_thresholds(dbi, tbl, operation);
+    } else {
+        if (args->debug >= 1) {
+            sprintf(logbuffer, "Cannot refind table %s", tbl->table_name);
+            log_entry(logbuffer, LVL_DEBUG);
+            fflush(LOGOUTPUT);
+        }
+    }
     if (args->debug >= 2)
         print_table_info(tbl);
 }
--
David Gould                      daveg@sonic.net
If simplicity worked, the world would be overrun with insects.