On 4 February 2010 10:02, Amitabh Kant <amitabhkant@gmail.com> wrote:
> On Wed, Feb 3, 2010 at 10:05 PM, Ivan Voras <ivoras@freebsd.org> wrote:
>>
>> On 02/03/10 16:10, Amitabh Kant wrote:
>>>
>>> Hello
>>>
>>> I have a server dedicated for Postgres with the following specs:
>>>
>>> RAM 16GB, 146GB SAS (15K) x 4 - RAID 10 with BBU, Dual Xeon E5345 @
>>> 2.33GHz
>>> OS: FreeBSD 8.0
>>
>> If you really do have "heavy read and write" load on the server, nothing
>> will save you from the bottleneck of having only 4 drives in the system (or
>> more accurately: adding more memory will help reads but nothing helps writes
>> except more drivers or faster (SSD) drives). If you can, add another 2
>> drives in RAID 1 and move+symlink the pg_xlog directory to the new array.
>
> Can't do anything about this server now, but would surely keep in mind
> before upgrading other servers. Would you recommend the same speed
> drives(15K SAS) for RAID 1, or would a slower drive also work here (10K SAS
> or even SATA II)?
Again, it depends on your load. It would probably be best if they are
approximately the same speed; the location of pg_xlog will dictate
your write (UPDATE / INSERT / CREATE) speed.
Writes to your database go like this: the data is first written to the
WAL (this is the pg_xlog directory - the transaction log), then it is
read and written to the "main" database. If the main database is very
busy reading, transfers from WAL to the database will be slower.