[Gluster-devel] lookup caching
Olivier Le Cam
Olivier.LeCam at crdp.ac-versailles.fr
Thu Apr 8 10:19:52 UTC 2010
Raghavendra G wrote:
> Well, as far as I understand the problem is rather that folders on
> the path of the targeted file are not cached at all by io-cache.
> Did you mean caching dentries, when you said "caching directories"?
> io-cache only caches file data. Also note that it is not a translator
> which does metadata (stats) caching.
That's it. Metadata caching is exactly what I would like to implement
but I haven't been able to find which part of code is dealing with
metadatas so far.
> This is why accessing a file makes (quite a lot) network traffic and
> can introduce bottlenecks because each folder is stated on the
> servers before delivering the file, even if that file is indeed
> cached by io-cache.
> io-cache only sends stat on the file being read not to all of its parent
> directories. I am not getting the reason you are concerned with too many
> stat calls. io-cache (during read and when file is cached) only sends a
> single stat call and that too if "cache-timeout" number of seconds have
> been elapsed since last validation.
Well I know understand that I don't have to focus my attention on
io-cache at all anymore.
In order to reach acceptable performances for my webfarm (at least the
same than I have with an NFS server), I really have to find a way for
limiting as much as possible stat calls over the network. Stat calls
introduce too much latency before the glusterfs client is able to
deliver a file (even with io-cache enabled). This makes performances
Note: I'm not concerned at all by file being modified by other clients.
The frontal reverse-proxy always forwards http connections to the same
webserver (according to the domain name), but in case of failover.
Having matadatas caching would then __greatly__ improve overall
performance in this situation!
Hope you can put me on the right way, please!
Thanks and best regards,
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