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SubjectRe: Journalling of Metadata in ext2fs?
Date
"Stephen C. Tweedie" wrote:
>Hi,
>
>Matthew Kirkwood writes:
>
> > Linux does not support synchronous metadata, except as a side-effect of
> > completely synchronous filesystems. Stephen Tweedie (sct@redhat.com) is
> > working on journalling extensions to ext2 and the vfs/block device layers,
> > but I doubt you'll see them before mid-2.3. They're described in a paper
> > at ftp://ftp.uk.linux.org/pub/linux/sct/fs/jfs/.
> >
> > Stephen - could some of the API be exported to userspace for use by things
> > like databases which want similar transaction support?
>
>No, the requirements of filesystems are very specialised: in
>particular you know you are only going to be dealing with small sets
>of updates, and you have very relaxed locking requirements.
>General-purpose application-level journaling is MUCH more complex ---
>get a database, that's what they are there for.
>
>Note that libdb2 in glibc supports transactions, btw.
>
>--Stephen
>

If copy-on-write was supported for files, you could use it for simple
journaling - c-o-w copy the file, modify the new version, delete the
old. This provides protection against application crash more than
system crash though, I would imagine.

-----kbealier.at.stny.lrun.com-------------------------------------
*Don't* background it, just sit there looking at it. Tell
everyone "I'll get back to you as soon as this here job is
finished". Very relaxing.

-- Lars P. Fischer


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