Re: Hot Standby 0.2.1

Heikki Linnakangas wrote:
> The problem becomes a lot easier if we accept that it's OK to have a
> lock included in the running-xacts snapshot and also appear in a
> XLOG_RELATION_LOCK record later. The standby should handle that
> gracefully already. If we just remove RecoveryInfoLock, that can happen,
> but it still won't be possible for a lock to be missed out which is what
> we really care about.

I see the problem with that now. Without the lock, it's possible that
the XLOG_RELATION_LOCK WAL record is written before the
XLOG_RUNNING_XACTS record. If the lock is not included in the snapshot,
we want the lock WAL record to be after the snapshot record.

So i guess we'll need the RecoveryInfoLock. But we don't need to hold it
across the wait. I think it's enough to acquire it just before writing
the WAL record in LockAcquire. That will ensure that the WAL record
isn't written until the snapshot is completely finished.

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