Re: BUG #3833: Index remains when table is dropped

I encountered this bug recently - and thought I'd have a try at seeing
what might fix it.

Taking an exclusive lock on the to-be-dropped table immediately (i.e in
RemoveRel) seems to be enough to prevent the drop starting while an
index is being created in another session. So it "fixes" the issue -
possible objections that I can think of are:

1/ Not a general solution to multi session dependent drop/create of
objects other than tables (unless we do 2/)
2/ Using this approach in all object dropping code may result in
deadlocks (but is this worse than dangling/mangled objects?)

Now, I'm conscious that there could be other show stopper reasons for
*not* doing this that I have not thought of, but figured I'd post in
case the idea was useful. Thoughts?

Cheers

Mark
*** src/backend/commands/tablecmds.c.orig    Wed Jan  2 13:58:05 2008
--- src/backend/commands/tablecmds.c    Wed Jan  2 13:46:43 2008
***************
*** 514,519 ****
--- 514,522 ----
      object.objectId = relOid;
      object.objectSubId = 0;

+     //Try a lock here!
+     LockRelationOid(relOid, ExclusiveLock);
+
      performDeletion(&object, behavior);
  }