Re: Linux I/O schedulers - CFQ & random seeks

Hello,

> Once we ramped up production traffic on the machines, PostgreSQL
> pretty much died under the load and could never get to a steady state.
> I think this had something to do with the PG backends not having
> enough I/O bandwidth (due to CFQ) to put data into cache fast enough.
> This went on for an hour before we decided to switch back to deadline.
> The system was back to normal working order (with 5-6x the I/O
> throughput of CFQ) in about 3 minutes, after which I/O wait was down
> to 0-1%.
>
> We run a (typical?) OLTP workload for a web app and see something like
> 2000 to 5000 req/s against PG.
>
> Not sure if this helps in the OP's situation, but I guess it's one of
> those things you need to test with a production workload to find out.
> :)

Me too. :) I tried switching schedulers on busy Oracle server and
deadline gave +~30% in our case (against CFQ). DB was on HP EVA
storage. Not 5-6 fold increase but still "free" +30% is pretty nice.
CentOS 5.5.

Regards,

Mindaugas