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

From: Alvaro Herrera
Subject: Re: moving pg_xlog -- yeah, it's worth it!
Date: ,
Msg-id: 20100212201106.GH3737@alvh.no-ip.org
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In response to: Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner")
List: pgsql-performance

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moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
 Re: moving pg_xlog -- yeah, it's worth it!  (Jesper Krogh, )
  Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
   Re: moving pg_xlog -- yeah, it's worth it!  (Amitabh Kant, )
    Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
   Re: moving pg_xlog -- yeah, it's worth it!  (Bruce Momjian, )
    Re: moving pg_xlog -- yeah, it's worth it!  (Scott Marlowe, )
   Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
    Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
     Re: moving pg_xlog -- yeah, it's worth it!  (Aidan Van Dyk, )
      Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
 Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
  Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
   Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
    Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
     Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera, )
  Re: moving pg_xlog -- yeah, it's worth it!  (Greg Smith, )
   Re: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner", )
    Re: moving pg_xlog -- yeah, it's worth it!  (Ben Chobot, )

Kevin Grittner wrote:
> Alvaro Herrera <> 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.


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From: Greg Smith
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Subject: Re: moving pg_xlog -- yeah, it's worth it!