Re: Load distributed checkpoint

On 12/22/06, Takayuki Tsunakawa <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> wrote:
>
> From: Inaam Rana
> > Which IO Shceduler (elevator) you are using?
>
> Elevator? Sorry, I'm not familiar with the kernel implementation, so I
> don't what it is. My Linux distribution is Red Hat Enterprise Linux 4.0for AMD64/EM64T, and the kernel is
> 2.6.9-42.ELsmp. I probably havn't changed any kernel settings, except for
> IPC settings to run PostgreSQL.
>
>
There are four IO schedulers in Linux. Anticipatory, CFQ (default),
deadline, and noop. For typical OLTP type loads generally deadline is
recommended. If you are constrained on CPU and you have a good controller
then its better to use noop.
Deadline attempts to merge requests by maintaining two red black trees in
sector sort order and it also ensures that a request is serviced in given
time by using FIFO. I don't expect it to do the magic but was wondering that
it may dilute the issue of fsync() elbowing out WAL writes.

You can look into /sys/block/<device>/queue/scheduler to see which scheduler
you are using.

regards,
inaam

--
Inaam Rana
EnterpriseDB http://www.enterprisedb.com