Hi -
Apologize for my insistance, but would it be possible to help on the
stats caching? This seriously decreases performances with small files
readings!
I am volunteer to try to deal with stats caching by myself but I would
appreciate some guidance in order to know where I could interact in the
code for.
Thanks and best regards,
--
Olivier
Olivier Le Cam wrote:
Raghavendra G wrote:
On Fri, Apr 2, 2010 at 3:32 PM, Olivier Le Cam
<Olivier.LeCam@xxxxxxxxxxxxxxxxxxxxx
<mailto:Olivier.LeCam@xxxxxxxxxxxxxxxxxxxxx>> 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.
This is not the behaviour I would expected according to the doc: "If the
cached page for a file is greater than 'cache-timeout' seconds old,
io-cache translator forces a re-validation of the page. However the
cached page is verified against the mtime whenever possible and cache is
refreshed. Default is 1 second."
AFAIU, mtime is always verified (whenever possible). As a non native
english spoker I might misunderstood something thougth!
Anyway, I have tested with a cache-timeout of 60 seconds on a client:
according to the debug traces and tcpdump, cat'ing the same file several
times. I have no idea which protocols are involved here but there is
always some traffic between the client and the servers even where cat
issued within the cache interval.
My guess is that file is indeed cached by io-cache but that the client
always stats the server before delivering the file (either from the
cache or the glusterfs).
Debug log attached.
Kind regards,
------------------------------------------------------------------------
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