Re: moving pg_xlog -- yeah, it's worth it!

Kevin Grittner wrote:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> wrote:

> > Actually, a transaction that performed no writes doesn't get a
> > commit WAL record written, so it shouldn't make any difference at
> > all.
>
> Well, concurrent to the web application is the replication. Would
> asynchronous commit of that potentially alter the pattern of writes
> such that it had less impact on the reads?

Well, certainly async commit would completely change the pattern of
writes: it would give the controller an opportunity to reorder them
according to some scheduler. Otherwise they are strictly serialized.

> I'm thinking, again, of
> why the placement of the pg_xlog on a separate file system made such
> a dramatic difference to the read-only response time -- might it
> make less difference if the replication was using asynchronous
> commit?

Yeah, I think it would have been less notorious, but this is all
theoretical.

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.