From: Chuck Lever <chuck.lever@ORACLE.COM>
Subject: Re: reply cache
Date: Mon, 15 Oct 2007 12:57:16 -0400
Message-ID: <47139BEC.8030400@oracle.com>
References: <47139B20.7070805@cesca.es>
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Cc: nfs@lists.sourceforge.net
To: Jordi Prats <jprats@cesca.es>
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Jordi Prats wrote:
> According to the file fs/nfsd/nfscache.c (line 30 on 2.6.23), reply 
> cache is fixed size. Why is this a fixed size cache? Shouldn't be 
> relative to the number of nfsd threads? I've a server with this statistics:
> 
> rc 0 959398 336415498
> 
> By what I've been researching this means: 0 hits, 959398 misses (I 
> supose that means something like "recently deleted") and 336415498 not 
> in cache (and never has been). Is that right?

A DRC hit implies the client is retransmitting.  Not having any hits is 
a good thing -- it means your server is able to handle all your clients 
without much sweat.

> Modifying the CACHESIZE to a bigger size do you think it could enhance 
> NFS performance by getting some hits on the reply cache?

The server's DRC is not a performance feature.  It's a way for the 
server to detect replayed requests from the client.  In a perfect world, 
servers wouldn't even have one.

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