> Thursday, June 15, 2006, 11:48:57 PM, you wrote:
> SS> On Thu, Robert Milkowski wrote:
> >> Hello nfs-discuss,
> >> 
> >>   Sometimes on nfs servers I get below messages and then I have
> >>   performance problems. What are they about and what can I do about
> >>   this?
> >> 
> >> XXXX  rpcmod: [ID 851375 kern.warning] WARNING: svc_cots_kdup no slots free
> >> XXXX  last message repeated 700353 times
> SS> This is an error from the NFS server when it attempts to place
> SS> a request into the duplicate request cache and finds that
> SS> all of the ones in the duplicate request table are "in progress".
> SS> The maximum for the duplicate request cache is 1024.
> SS> The most effective way to increase the value is /etc/system
> SS> and the variable would be: rpcmod:cotsmaxdupreqs 
> And when it finds that all requests are 'in progress' - then what?
> Thank you for info.
> btw: it looks like A LOT of messages are being sent in that case to
> syslog and that is perhaps one of the things which kills performance
> and makes whole server unresponsive.

The NFS server will return an error to the client and the client will
resend the request; yes, performance will suffer.

The duplicate request cache is only used for non-idempotent NFS
operations (things like create,remove,write).  Getattr and lookup
requests will not be affected by this so your server could have
more than 1024 in progress requests.  Server is very busy but
it may also indicate issues with the underlying filesystem.

So the number of duplicate request cache entries should at least
match the number of available threads in the NFS server.


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