From: Stewart Smith <stewart@flamingspork.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Grozdan <neutrino8@gmail.com>, xfs@oss.sgi.com
Subject: Re: Transactional XFS?
Date: Fri, 17 Feb 2012 15:40:21 +1100 [thread overview]
Message-ID: <87vcn6xebu.fsf@flamingspork.com> (raw)
In-Reply-To: <20120216064230.GZ14132@dastard>
On Thu, 16 Feb 2012 17:42:30 +1100, Dave Chinner <david@fromorbit.com> wrote:
> > The worst part is working out the semantics as to not break existing apps
> > (without completely sacrificing concurrency).
>
> That doesn't seem like a show stopper to me.
>
> The part that I see is that it is basically impossible to do
> arbitrarily large transactions in a filesystem - they are limited by
> the size of the log. e.g. you can't have a user transaction that
> writes more data or modifies more data than the log allows in a
> single checkpoint/transaction. e.g. you can't just overwrite a 100MB
> file in a transaction and expect it to work. It might work if you've
> got a 2GB log, but if you've only got a 10MB log, then that
> overwrite transaction is full of fail.
We have this problem too. none of the solutions are particularly pretty,
and certainly do have a performance impact.
> It's issues that like that that doom the generic usefulness of
> userspace controlled filesystem transactions as part of the normal
> filesystem operation. If you need this sort of functionality, it has
> to be layered over the top of the filesystem to avoid filesystem
> atomicity limitations. i.e. another layer of tracking and
> journalling. And at that point you're talking about implementing a
> database on top of the filesystem in the filesystem....
As I said... it's tricky to solve all the problems :)
--
Stewart Smith
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next prev parent reply other threads:[~2012-02-17 4:40 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-15 19:15 Transactional XFS? Grozdan
2012-02-16 0:22 ` Dave Chinner
2012-02-16 1:01 ` Stewart Smith
2012-02-16 1:43 ` Dave Chinner
2012-02-16 5:38 ` Stewart Smith
2012-02-16 6:42 ` Dave Chinner
2012-02-17 4:40 ` Stewart Smith [this message]
2012-02-16 22:10 ` Peter Grandi
2012-02-16 12:01 ` Matthias Schniedermeyer
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