cache empties itself?
Michael S. Fischer
michael at dynamine.net
Fri Apr 4 18:11:23 CEST 2008
On Fri, Apr 4, 2008 at 3:20 AM, Sascha Ottolski <ottolski at web.de> wrote:
> you are right, _if_ the working set is small. in my case, we're talking
> 20+ mio. small images (5-50 KB each), 400+ GB in total size, and it's
> growing every day. access is very random, but there still is a good
> amount of "hot" objects. and to be ready for a larger set it cannot
> reside on the webserver, but lives on a central storage. access
> performance to the (network) storage is relatively slow, and our
> experiences with mod_cache from apache were bad, that's why I started
> testing varnish.
Ah, I see.
The problem is that you're basically trying to compensate for a
congenital defect in your design: the network storage (I assume NFS)
backend. NFS read requests are not cacheable by the kernel because
another client may have altered the file since the last read took
If your working set is as large as you say it is, eventually you will
end up with a low cache hit ratio on your Varnish server(s) and you'll
be back to square one again.
The way to fix this problem in the long term is to split your file
library into shards and put them on local storage.
Didn't we discuss this a couple of weeks ago?
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