Re: Slower performance after enabling async io on Oracle Linux
From: Matthias Hoys <matthias.hoys_at_gmail.com>
Date: Tue, 15 May 2012 06:16:46 -0700 (PDT)
Message-ID: <30866150.505.1337087806616.JavaMail.geo-discussion-forums_at_vbvx4>
On Tuesday, May 15, 2012 2:52:33 AM UTC+2, Mladen Gogala wrote:
> 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.
>
Date: Tue, 15 May 2012 06:16:46 -0700 (PDT)
Message-ID: <30866150.505.1337087806616.JavaMail.geo-discussion-forums_at_vbvx4>
On Tuesday, May 15, 2012 2:52:33 AM UTC+2, Mladen Gogala wrote:
> 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.
>
Using netstat -s, I think I found something:
Tcp:
1168305 active connections openings
264105 passive connection openings
910210 failed connection attempts
I'm no network specialist, but it seems like there are a huge amount of "failed connection attempts"?? Or is this normal for iSCSI, I never worked with iSCSI storage before...
Btw: we don't have a local disk, everything is on VMWare and the disks are on the iSCSI box.
Thanks for the help,
Matthias Hoys
Received on Tue May 15 2012 - 08:16:46 CDT