On 12/22/06, Takayuki Tsunakawa <tsunakawa.takay@jp.fujitsu.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 4.0 for 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