Re: Slower performance after enabling async io on Oracle Linux

From: Matthias Hoys <>
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:
> 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:


    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

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