Christopher E. Brown:
> On Sat, 4 Aug 2007, Wietse Venema wrote:
>
> > Christopher E. Brown:
> > > On Mon, 23 Jul 2007, Wietse Venema wrote:
> > >
> > > > Christopher E. Brown:
> > > > > True MailDir, and the extented Maildir+ are NFS clean.
> > > >
> > > > What happens with non-idempotent requests, such as:
> > > > - client requests link(tmp, new)
> > > > - server reply is lost
> > > > - server crashes and loses the request ID cache.
> > > > - client times out
> > > > - client requests link(tmp, new) (retransmission)
> > > > - server replies with error (file exists)
> > >
> > >
> > > Maybe I am missing somthing here, please fill me in if I am. I can think
> > > of corner cases where this could cause duplicate messages.
> > >
> > > It is not ideal, but better than losing the message. Also, while this
> > > would seem to me more likely to happen over NFS (timing less critical,
> > > larger window), I would think that a system crash at the wrong moment
> > > could trigger the same issue on most any filesystem.
> >
> > This is not a problem with LOCAL file systems (if the machine
> > crashes, then Postfix dies with it; transaction is not completed,
> > and the client remote SMTP client retransmits the messae some time
> > later).
> >
> > Wietse
>
> Ok, now I am confused. I though we were talking about maildir delivery or
> IMAP triggered folder to folder copy/move.
The discussion was about file systems; someone stated that maildir
eliminates all NFS related problems and I pointed out that maildir
doesn't overcome problems with some non-idempotent NFS operations.
> For maildir delivery I would assume that the accept fed to the remote on
> commit to the local queue had already happened, and that the deliver (via
> local or maildrop) would fail on the dup filename, and tempfail the
> delivery. When the retry happens the timestamp based portion of the
> created file would be different and the local mailbox delivery would go
> through.
The maildir definition does not say what errors are hard or what
errors are retryable. Therefore you can have either one delivery
(link errors are hard errors; mail is returned to sender) or
duplicate delivery (link error is soft error; the second attempt
usually succeeds).
Wietse
> For the copy/move we would see a "failed" copy that actually worked, or a
> move that failed leaving both the original and the new copy in place.
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