Re: Slower performance after enabling async io on Oracle Linux

> Hello,
>
> Platform is Oracle Linux 6.2 64-bit with Oracle 11.2.0.3 64-bit.
>
> After enabling async io, I see slower performance for data pump exports,
> RMAN backups and long-running queries (between 10 and 15% slower).
>
> I enabled async io with:
>
> ALTER SYSTEM SET FILESYSTEMIO_OPTIONS=SETALL SCOPE=SPFILE; aio-nr is
> 19052 and aio-max-nr is 1048576. Storage is on iSCSI.
>
> Anyone else with the same experience? Is extra tuning for async io
> possible on Oracle Linux?
>
> Thanks,
> Matthias Hoys

Matthias, I the problem may as well lie on the network side. Check netstat -s for timeouts, retransmits or packets being dropped. Depending on the hardware, you may want to use jumbo packets, increase rmem and wmem parameters. Below are two articles about tuning the network:

http://fasterdata.es.net/host-tuning/linux/ http://www.ibm.com/developerworks/linux/library/l-adfly/index.html

Problem with Linux is that it is not well instrumented, there is no wait event interface so you cannot use the same technique as with the database. You can use systemtap to explore the performance of the network layer and figure out what is taking so long. Also, hopefully your iSCSI traffic doesn't have to go through any firewall? Packet inspection can take time, just as with the customs office.

So, if you want a recipe, measure the duration of the system calls by using strace and systemtap. Check netstat -s, make sure that your network is optimally configured.

-- 
http://mgogala.byethost5.com