2008-01-04 17:11:58

by Rick Macklem

[permalink] [raw]
Subject: Re: A new NFSv4 server...

> heh, tell me about it. First I started out using rpcgen, then rewrote
> everything to do raw XDR decoding. OPEN is huge.
> IMO, OPEN should be split into multiple operations, probably one for
> each "OPEN arm". It's not like new opcode numbers are expensive.

As I hinted at, Open is the way it is, since Windows requires one Op
so that Open/Share locks can be implemented correctly. Anything else
would not have satisfied a Win client's requirements.

> One of my personal desires is for a high level of cache coherence
> throughout the system for all clients (though perhaps an admin could
> optionally relax this requirement). I'm a fan of Google's "Chubby", a
> distributed reliable filesystem that stalls client writes until cache
> invalidations for the associated byte range are processed for all
> interested clients.

Delegations provide cache coherency "in a sense". When a client has a
delegation, it knows that no-one else is writing the file. Unfortunately,
as soon as a client gets an Open without a delegation, in no longer
gets the conherency guarantee (and servers are completely free to not
issue delegations if they don't feel like doing so). A client can
re-open a file when it gets an Open without a delegation, but if the
server still doesn't give it a delegation, it can't do anything more.
(The re-open trick is useful for an Open that requires confirmation, since
the server can't issue a delegation for that case.)