Re: What exactly is postgres doing during INSERT/UPDATE ?

On Fri, Aug 28, 2009 at 8:19 PM, Jeff Janes<jeff.janes@gmail.com> wrote:
>> ---------- Forwarded message ----------
>> From: Joseph S <jks@selectacast.net>
>> To: Greg Smith <gsmith@gregsmith.com>, pgsql-performance@postgresql.org
>> Date: Fri, 28 Aug 2009 10:25:10 -0400
>> Subject: Re: What exactly is postgres doing during INSERT/UPDATE ?
>> Greg Smith wrote:
>>
>>> The main two things you can do to improve this on the database side:
>>>
>>> -Increase checkpoint_segments, which reduces how often updated data has
>>> to be flushed to disk
>>
>> It fsync is turned off, does this matter so much?
>
> It still matters.  The kernel is only willing to have so much dirty data
> sitting in the disk cache.  Once it reaches that limit, user processes doing
> writes start blocking while the kernel flushes stuff on their behalf.

it doesn't matter nearly as much though.  if you are outrunning the
o/s write cache with fsync off, then it's time to start looking at new
hardware.

merlin