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From Gurpreet Singh <gurpreet.si...@gmail.com>
Subject Re: kswapd0 causing read timeouts
Date Mon, 18 Jun 2012 18:57:17 GMT
Thanks for all the information Holger.

Will do the jvm updates, kernel updates will be slow to come by. I see that
with disk access mode standard, the performance is stable and better than
in mmap mode, so i will probably stick to that.
Are you suggesting i try out mongodb?

/G

On Mon, Jun 18, 2012 at 5:46 AM, Holger Hoffstaette <
holger.hoffstaette@googlemail.com> wrote:

> On Thu, 14 Jun 2012 11:08:39 -0700, Gurpreet Singh wrote:
>
> > JNA is installed. swappiness was 0. vfs_cache_pressure was 100.
> [..]
> > Right now, i am handling only 80 gigs of data. kernel version is 2.6.26.
> > java version is 1.6.21
>
> - your JVM is way too old and will leak native memory when you use JMX.
> Use either latest JDK6 or try 7u5, works for me.
>
> - your kernel is way too old and suffers from kswapd going crazy
> *especially* when swappiness=0, which *does not do what you think it
> does*. Upgrade your kernel (latest stable 3.3.x is good, 3.4.3 works for
> me too). This has nothing to do with Cassandra, other people have found
> the same problem (esp. with old RH "Enterprise" kernels).
>
> - don't set swappiness=0 unless you add a kernel patch (to 3.4.x) that
> will be part of 3.5 (http://t.co/l0XyLkCg) and which will have the effect
> that people expect. This works *really* great, and swapping only occurs
> when absolutely necessary - e.g. when an app is leaking memory.
>
> - vfs_cache_pressure has no play in any of this.
>
> - use sysctl to check that vm.dirty_background_ratio and vm.dirty_ratio
> are in the low single-digits (like say 2 & 4). This will lead to less
> bursty writeout activity.
>
> Cassandra's (current) use of mmap is far from optimal, but when the JVM
> and kernel are not doing what they are supposed to do, it can become
> especially "harmful". Just look at MongoDB.
>
> -h
>
>
>

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