Re: [HACKERS] snapbuild woes

Hi,

On 2016-12-10 23:10:19 +0100, Petr Jelinek wrote:
> Hi,
> First one is outright bug, which has to do with how we track running
> transactions. What snapbuild basically does while doing initial snapshot
> is read the xl_running_xacts record, store the list of running txes and
> then wait until they all finish. The problem with this is that
> xl_running_xacts does not ensure that it only logs transactions that are
> actually still running (to avoid locking PGPROC) so there might be xids
> in xl_running_xacts that already committed before it was logged.

I don't think that's actually true?  Notice how LogStandbySnapshot()
only releases the lock *after* the LogCurrentRunningXacts() iff
wal_level >= WAL_LEVEL_LOGICAL.  So the explanation for the problem you
observed must actually be a bit more complex :(

Regards,

Andres