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From Leif Hedstrom <zw...@apache.org>
Subject Re: Understanding ATS memory usage
Date Tue, 23 Jan 2018 10:12:06 GMT


> On Jan 23, 2018, at 7:36 PM, Veiko Kukk <veiko.kukk@gmail.com> wrote:
> 
> Hi again,
> 
> During that mysterious task that happens after ~ 50-51 minutes causes requests/responses
to slow down very much, even time out.
> Requests that usually take few hundred milliseconds are now taking over 30s and timing
out. This happens only during that time when memory consumption is suddenly dropped by ATS.
Happens for both bypassed urls and for hits.
> ATS version is 7.1.1 and this looks like serious bug for me.


That sounds suspiciously like kernel paging activity, maybe it’s spending that time dumping
flushing dirty pages?  Maybe transparent huge pages ? Or tweak the sysctl’s for dirty page
ratios?

The other thing to possibly look at is the dir entry sync periods of ATS. Whenever we sync
those to disk, we consume both more memory and more disk I/O, and maybe you are putting too
much pressure on the VM (i.e. maybe you need to turn down the RAM cache or tweak the amount
of directory entries you have).

— Leif

E.g.

https://lonesysadmin.net/2013/12/22/better-linux-disk-caching-performance-vm-dirty_ratio/
<https://lonesysadmin.net/2013/12/22/better-linux-disk-caching-performance-vm-dirty_ratio/>



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