Re: Issues with two-server Synch Rep

On Mon, Oct 11, 2010 at 9:29 PM, Josh Berkus <josh@agliodbs.com> wrote:
>>>> What is your source for those numbers?  They could be right, but I
>>>> simply don't know.
>>> pg_bench tests with asynch rep and standby_delay = 0.  Not rigorous, but
>>> enough to show that there is a problem there.  Doing pg_bench with a
>>> small database
>>
>> Interesting.
>
> Yeah, it occurs to me that we can "fix" this with cleanup_delay on the
> master, but that's a much worse solution than XID publication from the
> standby.  It means bloat *all* the time instead of just some of the time.

Yeah, that's worse, I think.

> I think we have Yet Another Knob here: users whose standby is
> essentially idle will NOT want XID publication, and users whose standby
> is for load-balancing will.

There probably is a knob, but XID publication ought to be basically
free on an idle standby, so the real trade-off is between query
cancellation or replay delay on the standby, vs. cluster-wide bloat.

>> Sure.  But we can't forever ignore the fact that trigger-based
>> replication is not as performant as log-based replication.
>
> Watch me.  ;-)

s/can't/shouldn't/ ?

--
Robert Haas
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