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Re: [Gluster-devel] lookup caching

From: Raghavendra G
Subject: Re: [Gluster-devel] lookup caching
Date: Sat, 3 Apr 2010 17:10:42 +0400

On Fri, Apr 2, 2010 at 3:32 PM, Olivier Le Cam <address@hidden> wrote:
Hi -

I am evaluating glusterfs for a replacement of an NFS server which acts as a backend storage for a webcluster, in order to take advantage of its very interesting features in term of high-availability and scalability.

That said, I'm experiencing (like everybody in the same situation) performance issues due to the large number of small files a webserver have to deal with. 

The io-cache translator does not help so much in this situation because (as far as I understood) the clients always have to check the mtime of the target file before delivering it in order to known if the cache is up-to-date. This intensive network traffic is quite penalizing in term of performance (especially on a Gb-E).

Following to a recent talk on the IRC channel, it came to my mind that caching lookups could (in this particular situation) greatly improve the performances.

If you are not very much concerned about file being changed from other clients while it is being cached, you can set 'cache-timeout' value in io-cache configuration to some high value, there by increasing the time intervals at which stat call is sent to server to check whether the file has changed.

I have observed the GlusterFS code carefully and TBH I haven't been able to see how/where such a translator could be integrated in.

Would it be possible to get some help? Are other users/developers already involved in such a development?

If you are just interested in caching stats for beniefit of io-cache, the same functionality can be achieved by tuning cache-timeout value in io-cache.

I don't want to bother you more than necessary, getting few advices would be enough in order to put me on the way.

I'll appreciate any comments or pointers.

Thanks and best regards,

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Raghavendra G

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