On Aug 17, 2011, at 1:56 PM, Tomas Vondra wrote:
> On 17 Srpen 2011, 18:39, Ogden wrote:
>>> Yes, but it greatly depends on the amount of WAL and your workload. If
>>> you
>>> need to write a lot of WAL data (e.g. during bulk loading), this may
>>> significantly improve performance. It may also help when you have a
>>> write-heavy workload (a lot of clients updating records, background
>>> writer
>>> etc.) as that usually means a lot of seeking (while WAL is written
>>> sequentially).
>>
>> The database is about 200Gb so using /usr/local/pgsql/pg_xlog on a virtual
>> disk with 100Gb should not be a problem with the disk space should it?
>
> I think you've mentioned the database is on 6 drives, while the other
> volume is on 2 drives, right? That makes the OS drive about 3x slower
> (just a rough estimate). But if the database drive is used heavily, it
> might help to move the xlog directory to the OS disk. See how is the db
> volume utilized and if it's fully utilized, try to move the xlog
> directory.
>
> The only way to find out is to actualy try it with your workload.
Thank you for your help. I just wanted to ask then, for now I should also put the xlog directory in the /var/lib/pgsql
directorywhich is on the RAID container that is over 6 drives. You see, I wanted to put it on the container with the 2
drivesbecause just the OS is installed on it and has the space (about 100Gb free).
But you don't think it will be a problem to put the xlog directory along with everything else on /var/lib/pgsql/data? I
hadseen someone suggesting separating it for their setup and it sounded like a good idea so I thought why not, but in
retrospectand what you are saying with the OS drives being 3x slower, it may be okay just to put them on the 6 drives.
Thoughts?
Thank you once again for your tremendous help
Ogden
