Re: Need to tune for Heavy Write

On Thu, Aug 4, 2011 at 6:41 AM, Nicholson, Brad (Toronto, ON, CA)
<bnicholson(at)hp(dot)com> wrote:
>> -----Original Message-----
>> From: pgsql-performance-owner(at)postgresql(dot)org [mailto:pgsql-performance-
>> owner(at)postgresql(dot)org] On Behalf Of Scott Marlowe
>> Sent: Thursday, August 04, 2011 4:46 AM
>> To: Willy-Bas Loos
>> Cc: Adarsh Sharma; pgsql-performance(at)postgresql(dot)org
>> Subject: Re: [PERFORM] Need to tune for Heavy Write
>>
>>
>> > Moving the pg_xlog to a different directory only helps when that
>> > directory is on a different harddisk (or whatever I/O device).
>>
>> Not entirely true.  By simply being on a different  mounted file
>> system this moves the fsync calls on the pg_xlog directories off of
>> the same file system as the main data store.  Previous testing has
>> shown improvements in performance from just using a different file
>> system.
>>
>
> Is this still the case for xfs or ext4 where fsync is properly flushing only the correct blocks to disk, or was this referring to the good old ext3 flush everything on fysnc issue?

Good question. One I do not know the answer to. Since I run my dbs
with separate pg_xlog drive sets I've never been able to test that.