Re: Toast issues with OldestXmin going backwards

>>>>> "Amit" == Amit Kapila <amit.kapila16@gmail.com> writes:

 >>> (Or do we need to track it across restarts? maybe we do, to deal with
 >>> replication slaves without slots, or changes in parameters)
 
 >> Yeah, I'm worried that it might need to be persistent across restarts.
 >> 
 >> One idea that occurred to me is to somehow record -- I guess in
 >> pg_class using non-transactional updates -- the last cutoff XID used
 >> to vacuum any given table.  Then we could just make a rule that you
 >> can't vacuum the TOAST table with an XID that's newer than the last
 >> one used for the main table.  That would preserve the property that
 >> you can vacuum the tables separately while avoiding dangling pointers.

 Amit> Won't this lead to a bloat in toast tables when there is a big
 Amit> difference between the cutoff XID of the main heap table and the
 Amit> latest values of OldestXmin?

Yes. What we need is actually the reverse of what Robert describes -
when we vacuum the _main_ table, we must use the _later_ of the
currently calculated OldestXmin or the OldestXmin last used to vacuum
the toast table.

-- 
Andrew (irc:RhodiumToad)