[ale] thoughts on reducing Sync time for 2.6.32 System?

[Erik Mathis]

I would also make sure the disk io scheduler is set to deadline.

-Erik-
On Jan 21, 2014 9:18 PM, "Neal Rhodes" <neal at mnopltd.com> wrote:

>  Searching on this more, I find
> http://www.westnet.com/~gsmith/content/linux-pdflush.htm
>
> How is this for a working hypothesis:
>
> Old Dell servers were 8GB, and I think our DB buffering might have used
> 2GB of that.
>
> New Dell servers are 24GB, and Progress OpenEdge is 64 bit, and uses a
> good bit more buffer space.
>
> */proc/sys/vm/dirty_background_ratio* is the same 10%, but that's 3X the
> amount of dirty accumulated.
>
> According to /proc/meminfo, I've seen Dirty: over 3013kB.
>
> It would seem that dropping */proc/sys/vm/dirty_background_ratio* to 6%
> might be worth a stab to see if it evens out the peak sync times.   It's
> not that the system is slow, it's just when we bust through a 3 second SLA
> the client goes bat-crazy.
>
> On Tue, 2014-01-21 at 20:57 -0500, Neal Rhodes wrote:
>
> So, the context is a pair of new Dell 24 core servers installed this year,
> running 2.6.32-431.1.2.0.1.el6.x86_64.
>
> This replaced older Dell servers running I don't remember what.
>
> Both old and new servers ran about 200,000 web service queries a day using
> Tomcat6 and Progress OpenEdge.
>
> The new servers, while faster at DB updates, will several times a month,
> usually during prime high volumes in early afternoon, exhibit a period of 3
> seconds of all DB updates being frozen.   When we've chased it down, it
> seems the DB has completed a checkpoint, and issued a sync call afterwards,
> and that freezes everyone until it completes.
>
> The older servers, while not as fast, didn't exhibit this behavior.
>
> I may be wrong about the sync being the culprit; that's what the timings
> in the DB logs seem to indicate.
>
> Is there any tuning parameters which would affect the amount of time for a
> sync to complete on a busy server?
>
> Neal Rhodes
> MNOP Ltd.
>
>
>
>
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