Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ames!apple!bloom-beacon!athena.mit.edu!jtkohl
From: jtkohl@athena.mit.edu (John T Kohl)
Newsgroups: comp.protocols.nfs
Subject: Re: NFS not idempotent (was re: mountd Performance under Stress)
Message-ID: <14068@bloom-beacon.MIT.EDU>
Date: 5 Sep 89 20:05:21 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: jtkohl@athena.mit.edu (John T Kohl)
Organization: Massachusetts Institute of Technology
Lines: 22

In article <1199@sequent.cs.qmc.ac.uk> liam@cs.qmc.ac.uk (William Roberts) writes:

   This is a difference between user-level RCP and kernel-level RPC.
   The kernel level *knows* that its NFS RPC requests are
   idempotent 

Unfortunately, some of them ARE NOT idempotent, and that has caused
great troubles to us at MIT.

Consider:
	create directory  (we've had mkdir return 'already exists' when
				it has actually just been created)
	set attributes with length = 0 (truncate--with packet reordering
				and multiple biod's/nfsd's, this can lead to
				truncation occuring after a successive
				write()--poof, your file contents are gone)
	rename
	move

John Kohl <jtkohl@ATHENA.MIT.EDU> or <jtkohl@Kolvir.Brookline.MA.US>
Digital Equipment Corporation/Project Athena
(The above opinions are MINE.  Don't put my words in somebody else's mouth!)