Re: Separating bgwriter and checkpointer

On Tue, Sep 20, 2011 at 11:01 AM, Marti Raudsepp <marti(at)juffo(dot)org> wrote:
> On Fri, Sep 16, 2011 at 01:53, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> This patch splits bgwriter into 2 processes: checkpointer and
>> bgwriter, seeking to avoid contentious changes. Additional changes are
>> expected in this release to build upon these changes for both new
>> processes, though this patch stands on its own as both a performance
>> vehicle and in some ways a refcatoring to simplify the code.
>
> While you're already splitting up bgwriter, could there be any benefit
> to spawning a separate bgwriter process for each tablespace?
>
> If your database has one tablespace on a fast I/O system and another
> on a slow one, the slow tablespace would also bog down background
> writing for the fast tablespace. But I don't know whether that's
> really a problem or not.

I doubt it. Most of the time the writes are going to be absorbed by
the OS write cache anyway.

I think there's probably more performance to be squeezed out of the
background writer, but maybe not that exact thing, and in any case it
seems like material for a separate patch.

--
Robert Haas
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