CLUSTER and MVCC

Is there a particular reason why CLUSTER isn't MVCC-safe? It seems to me 
that it would be trivial to fix, by using SnapshotAny instead of 
SnapshotNow, and not overwriting the xmin/xmax with the xid of the 
cluster command.

I feel that I must missing something, or someone would've already fixed 
it a long time ago...

Csaba, you mentioned recently 
(http://archives.postgresql.org/pgsql-hackers/2007-03/msg00027.php) that 
you're actually using the MVCC-violation to clean up tables during a 
backup. Can you tell us a bit more about that? Would you be upset if we 
shut that backdoor?

In any case, the MVCC-violation needs to be documented. I'll send a doc 
patch to pgsql-patches shortly.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com