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Re: [nfsv4] persistent sessions and compound atomicity

David Noveck <davenoveck@gmail.com> Thu, 10 December 2020 22:07 UTC

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From: David Noveck <davenoveck@gmail.com>
Date: Thu, 10 Dec 2020 17:07:27 -0500
Message-ID: <CADaq8jdYyigfkHDbAdk7uARzdSsoNHdPZdUJjPMka5_4tZ6C6Q@mail.gmail.com>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Rick Macklem <rmacklem@uoguelph.ca>, Tom Talpey <tom@talpey.com>, "nfsv4@ietf.org" <nfsv4@ietf.org>
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Subject: Re: [nfsv4] persistent sessions and compound atomicity
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On Wed, Dec 9, 2020, 5:59 PM J. Bruce Fields <bfields@fieldses.org> wrote:

> On Wed, Dec 09, 2020 at 04:43:59PM +0000, Rick Macklem wrote:
> > I would say that the ATOMIC refers to the individual operations of the
> > compound. In other words, it must cache the reply to each operation
> > when it is completed, in the persistent cache.
> >
> > Then, if a retry of the compound is received after a server reboot,
> > the reply for the first K operations that were completed prior to the
> > reboot are generated from the cache and the remaining N-K are
> > performed on the file system to complete the reply. (At least for the
> > non-idempotent operations in the compound.)
> >
> > For this to all work correctly, I think the server file system would
> > need to perform each non-idempotent operation ATOMICALLY as well, such
> > that after the reboot the file system is in either the pre-operation
> > or post-operation state.
>
> Great, sounds like everyone agrees, I'll calm down.
>

I don't see the need for individual ops to be atomic especially since they
(e.g. writes) are not defined as atomic in general.

I don't think we have total agreement but we are moving in the same
direction.  No reason to be anything but calm.
.

>
> > rick, who has no intention of ever trying to implement a persistent
> > session cache.
>

Your input is still valuable.


> I can't decide.  It looks like kind of a pain.  It'll require some
> cooperation with the filesystem folks--I think it needs to be integrated
> with filesystem journaling somehow.
>

That makes sense.


> But I'm not looking forward to someone running into this, and having to
> say, "oh yeah, we've known about that bug for decades; just give me
> another few months or a year, and I'll fix it right up for you...."
>

I have a revised version of this section in draft-dnoveck-rfc5661bis-00.
(Will be out before next year).  I hope we will discuss that and get to a
text that everybody does agree on, and might even be implementable :-)

>
> --b.
>
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