From owner-freebsd-fs Thu Oct 2 21:29:31 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id VAA15498 for fs-outgoing; Thu, 2 Oct 1997 21:29:31 -0700 (PDT) Received: from parkplace.cet.co.jp (parkplace.cet.co.jp [202.32.64.1]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id VAA15492 for ; Thu, 2 Oct 1997 21:29:25 -0700 (PDT) Received: from localhost (michaelh@localhost) by parkplace.cet.co.jp (8.8.5/CET-v2.1) with SMTP id EAA04260; Fri, 3 Oct 1997 04:28:27 GMT Date: Fri, 3 Oct 1997 13:28:27 +0900 (JST) From: Michael Hancock To: Terry Lambert cc: ccsanady@bob.scl.ameslab.gov, brandon@roguetrader.com, wilko@yedi.iaf.nl, freebsd-fs@FreeBSD.ORG Subject: Re: Known problems with async ufs? In-Reply-To: <199710020815.BAA24245@usr08.primenet.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-fs@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk On Thu, 2 Oct 1997, Terry Lambert wrote: > > > It will also mean that there are no hooks to guarantee transactions > > > are idempotent (multiple atomic transactions considered as an > > > all-or-nothing unit) for something like a user accessible transaction > > > tracking system. > > > > I think you're looking for another term. Idempotent transactions are like > > reads where you can repeat the transaction without ill-effects. > > Non-idempotent transactions modify the state of the system such that they > > can't be repeated, say rmdir foo. > > > > Multiple atomic transactions that are atomic can be restated as an atomic > > transaction. > > Reads advance the file pointer, unless they are mread. Same for write vs. > mwrite. Maybe getattr would have been a better example. Though I've seen references where they separate VOP operations into idempotent and non-idempotent operations. It's probably more important in the context of NFS servers where things are stateless. A read here is packaged with file positioning so repeated receives of the same request doesn't hurt anything. Regards, Mike