Re: Why does splitting $PGDATA and xlog yield a performance benefit?

On Tue, Aug 25, 2015 at 10:16:37AM PDT, Andomar wrote:
> >However, I know from experience that's not entirely true, (although it's not always easy to measure all aspects of
yourI/O bandwith). 
> >
> >Am I missing something?
> >
> Two things I can think of:
>
> Transaction writes are entirely sequential.  If you have disks
> assigned for just this purpose, then the heads will always be in the
> right spot, and the writes go through more quickly.
>
> A database server process waits until the transaction logs are
> written and then returns control to the client. The data writes can
> be done in the background while the client goes on to do other
> things.  Splitting up data and logs mean that there is less chance
> the disk controller will cause data writes to interfere with log
> files.
>
> Kind regards,
> Andomar
>

hmm, yeah those are both what I'd lump into "I/O bandwith".
If your disk subsystem is fast enough, or you're on a RAIDd SAN
or EBS you'd either overcome that, or not neccssarily be able to.