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

From: Kevin Grittner
Subject: Re: moving pg_xlog -- yeah, it's worth it!
Date: ,
Msg-id: 4B750193020000250002F22D@gw.wicourts.gov
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In response to: moving pg_xlog -- yeah, it's worth it!  ("Kevin Grittner")
Responses: Re: moving pg_xlog -- yeah, it's worth it!  (Alvaro Herrera)
Re: moving pg_xlog -- yeah, it's worth it!  (Greg Smith)
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, )

Hannu Krosing  wrote:

> Can it be, that each request does at least 1 write op (update
> session or log something) ?

Well, the web application connects through a login which only has
SELECT rights; but, in discussing a previous issue we've pretty well
established that it's not unusual for a read to force a dirty buffer
to write to the OS.  Perhaps this is the issue here again.  Nothing
is logged on the database server for every request.

> If you can, set
>
> synchronous_commit = off;
>
> and see if it further increases performance.

I wonder if it might also pay to make the background writer even more
aggressive than we have, so that SELECT-only queries don't spend so
much time writing pages.  Anyway, given that these are replication
targets, and aren't the "database of origin" for any data of their
own, I guess there's no reason not to try asynchronous commit.
Thanks for the suggestion.

-Kevin




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