Life cycles of tuple descriptors

Hi,

There are some things about the life cycle of the common TupleDesc
that I'm not 100% sure about.

1. In general, if you get one from relcache or typcache, it is
   reference-counted, right?

2. The only exception I know of is if you ask the typcache for
   a blessed one (RECORD+typmod), and it is found in the shared-memory
   cache. It is not refcounted then. If it is found only locally,
   it is refcounted.

3. Is that shared case the only way you could see a non-refcounted
   TupleDesc handed to you by the typcache?

4. How long can such a non-refcounted TupleDesc from the typcache
   be counted on to live?

   There is a comment in expandedrecord.c: "It it's not refcounted, just
   assume it will outlive the expanded object."

   That sounds like confidence, but is it confidence in the longevity
   of shared TupleDescs, or in the fleeting lives of expanded records?

   The same comment says "(This can happen for shared record types,
   for instance.)" Does the "for instance" mean there are now, or just
   in future might be, other cases where the typcache hands you
   a non-refcounted TupleDesc?

5. When a constructed TupleDesc is blessed, the copy placed in the cache
   by assign_record_type_typmod is born with a refcount of 1. Assuming every
   later user of that TupleDesc plays nicely with balanced pin and release,
   what event(s), if any, could ever occur to decrease that initial 1 to 0?

Thanks for any help getting these points straight!

Regards,
-Chap