Re: Tuning scenarios (was Changing the default configuration)

Robert,

> >     1) Location of the pg_xlog for heavy-update databases.
>
> I see you put this up pretty high on the list. Do you feel this is the
> most important thing you can do? For example, if you had a two drive
> installation, would you load the OS and main database files on 1 disk
> and put the pg_xlog  on the second disk above all other configurations?

Yes, actually.   On machines with 2 IDE disks, I've found that this can make
as much as 30% difference in speed of serial/large UPDATE statements.

> Ideally I recommend 3 disks, one for os, one for data, one for xlog; but
> if you only had 2 would the added speed benefits be worth the additional
> recovery complexity (if you data/xlog are on the same disk, you have 1
> point of failure, one disk for backing up)

On the other hand, with the xlog on a seperate disk, the xlog and the database
disks are unlikely to fail at the same time.  So I don't personally see it as
a recovery problem, but a benefit.

--
-Josh Berkus
 Aglio Database Solutions
 San Francisco