Re: [NFS] NFS Digest, Vol 18, Issue 70 (NFS performance problems)

["J. Bruce Fields" <bfields@fieldses.org>]

On Fri, Nov 30, 2007 at 11:27:16AM -0500, Wendy Cheng wrote:
> Trond Myklebust wrote:
>> Actually, the real problem would be dealing with something like
>> unlink('foo') followed by open('foo', O_CREAT|O_EXCL). How do you ensure
>> that a replay of those actions following a reboot is fully consistent in
>> the face of some other client attempting an open('foo', O_CREAT) at the
>> same time?
>>
>> The problem is that a number of directory operations involve exclusive
>> semantics, and so cannot be replayed. The solution to this sort of
>> problem is going to have to involve exclusive (i.e. write) directory
>> delegations to ensure that whatever transactions one client performs
>> cannot interfere with the transactions performed by another.
>>
>>   
>
> Well, a dumb question from me (borrowing Bruce's line :) ) ... even with 
> "sync" in place, when server rebooted, the RPC reply cache is gone. How 
> does linux server handle re-transmitted non-idempotent requests ?

Badly!

Somebody should figure out whether it would be possible for us to
implement persistent sessions in v4.1:

	http://www.nfsv4-editor.org/draft-17/draft-ietf-nfsv4-minorversion1-17.html#Persistence

It looks hard!

--b.

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