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Re: [Gluster-devel] lookup caching

From: Raghavendra G
Subject: Re: [Gluster-devel] lookup caching
Date: Sat, 3 Apr 2010 17:02:38 +0400

On Fri, Apr 2, 2010 at 5:49 PM, Stephan von Krawczynski <address@hidden> wrote:
On Fri, 02 Apr 2010 14:41:36 +0100
Gordan Bobic <address@hidden> wrote:

> On 02/04/2010 12:32, Olivier Le Cam wrote:
> > 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.
> Maybe some of the devs can explain whether this is plausible, but I
> somewhat doubt it. You would lose the integrity guarantees.

If you're talking of data integrity here I doubt that it is there at all.
Yesterday I checked a configuration with 2.0.9 replication and 3 clients with
iocache. I found out that if I edit an ascii file on one client and save it
back being the same size as before, another client still sees the old file
content. I checked the servers and found that they all contained the correct
new file version. So the data integrity is broken anyway when using iocache on

This is quite expected, since the client on which the data is being read has cached the data. io-cache has cache-timeout option which can be tuned to force the clients to check whether the file has changed on server after configured time intervals.

However also please note that, if the file is being modified and read from the same client, this issue would/should not have happened.

> Gordan


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