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Re: Odd cache behavior

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File Name File Size   Posted by Date  
localhost-df-day.png 16.5 KB open | download Jim Ohlstein 10/02/2009 Read message
localhost-df-month.png 20.1 KB open | download Jim Ohlstein 10/02/2009 Read message
localhost-df_inode-day.png 16.3 KB open | download Jim Ohlstein 10/03/2009 Read message
localhost-df_inode-month.png 19.6 KB open | download Jim Ohlstein 10/03/2009 Read message
October 06, 2009 08:04AM
On Tue, Oct 06, 2009 at 03:46:48PM +0400, Igor Sysoev wrote:

> On Sat, Oct 03, 2009 at 09:54:59AM -0400, Jim Ohlstein wrote:
>
> > Igor Sysoev wrote:
> > > On Fri, Oct 02, 2009 at 01:07:24PM -0400, Jim Ohlstein wrote:
> > >
> > >> Hello,
> > >>
> > >> I'm seeing odd disk usage statistics for my cache. The cache is
> > >> primarily of small files (images, javascript, and css) and sits on a
> > >> 128GB SSD using ext2 file system mounted with "noatime" option. The
> > >> cache is all that the the drive is being used for at this time.
> > >>
> > >> The attached graphs were generated by Munin using df. The data from du
> > >> correlates closely with df when run manually.
> > >>
> > >> As you can see, periodically, with no set interval, disk usage rises
> > >> gradually, and then drops precipitously. I don't see anything out of the
> > >> ordinary in the error log. The cache serves about 2.8-3 million requests
> > >> per day, up from ~2.2-2.4 million one month ago.
> > >>
> > >> The cache config is:
> > >>
> > >> fastcgi_cache_path /falcon/cache levels=1:2 keys_zone=one:1024m
> > >> inactive=1d max_size=80g;
> > >>
> > >> where the SSD is mounted as /falcon.
> > >
> > > As I understand /falcon is used solely for nginx cache ?
> >
> > This is correct.
> >
> > > Could you monitor inode usage also ?
> >
> > See attached graphs.
> >
> > > Did you restart nginx in the times of the drops or not ?
> >
> > No.
> >
> > > Currently I have no idea why it may be.
>
> I saw the similar pattern, when nginx is restarted (not reHUPed) at the cliff
> growing start point: then cache loader loads many old inactive cache items
> and sets close inactivity timers for the items. Therefore cache size grows
> lineary and at some time all these inactive items are purged almost
> simultaneously causing precipitous drop.
>
> Have you restarted nginx at the growing start points ?

A note: the lineary growth period is equal to an "inactive=" parameter in
fastcgi_cache_path.


--
Igor Sysoev
http://sysoev.ru/en/
Subject Author Posted

Odd cache behavior Attachments

Jim Ohlstein October 02, 2009 01:14PM

Re: Odd cache behavior

Igor Sysoev October 03, 2009 05:28AM

Re: Odd cache behavior Attachments

Jim Ohlstein October 03, 2009 10:02AM

Re: Odd cache behavior

Igor Sysoev October 06, 2009 07:56AM

Re: Odd cache behavior

Igor Sysoev October 06, 2009 08:04AM

Re: Odd cache behavior

Igor Sysoev October 06, 2009 09:00AM

Re: Odd cache behavior

Jim Ohlstein October 06, 2009 09:52AM



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