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Re: [DESIGN] mtime versioning - was: Getting Bug 1256 fixed

From: John Szakmeister <john_at_szakmeister.net>
Date: 2005-11-28 12:59:18 CET

On Monday 28 November 2005 06:25, Julian Foad wrote:
> Malcolm Rowe wrote:
> > On Mon, Nov 28, 2005 at 09:59:06AM +0100, Ph. Marek wrote:
> >>- space on harddisk - this is *currently* important! A wc with 1000 files
> >> with no properties other than svn:text-time on a 4kB filesystem needs
> >> 1000 * 2 * 4k ~ about 8MByte *only for this properties*!
> >> Now go to a wc with 100000 files ... and 800M are gone.
>
> You say "800M are gone" as if it's a bad thing, but if the whole WC
> occupies 10 GB or so then it's trivial.

True, for a large working copy in terms of raw size. However, if you have
100,000 files that are all pretty small (source files, for example). Then
it's possible that the props are occupying a significant amount of space in
relation to the overall size of the WC.

> >> Although matters are progressing on this front.
> >
> > That's quite significant. Also, files do not typically have properties
> > (with the possible exception of svn:eol-style), and there's a fair amount
> > of optimisation that's been done lately to improve matters in that case.
> > Adding svn:text-time to all files unconditionally would probably be a
> > bad idea.
>
> You're both doing "premature optimisation". Concentrate on what would be
> functionally desirable, and THEN determine if we need to make any
> improvementes in efficiency, and we'll make them. Mention the inefficiency
> as a caveat, don't treat it as a show-stopper.

/me agrees.

> > [Note that the FSFS format has the capability to store properties as
> > deltas against earlier versions, but the implementation doesn't currently
> > do that, presumably at least partly because properties are considered to
> > be things that change infrequently - and so doing so probably wouldn't
> > be worth the effort in terms of space saved, and would also mean it
>
> Looks like you got your argument back to front there :-)
>
> > would take longer to reconstruct the properties during a read.]
>
> Premature optimisation again - unless you have measured that speed loss and
> found it to be unacceptably large, which I seriously doubt.

FWIW, I don't think the time difference would be all that significant.
Properties change a lot less than the underlying file, so I believe the
number of deltas involved would be considerably smaller than what you would
expect for a file. BTW, there are some people out there putting quite a bit
of information into their properties (>1MB), so perhaps we should really take
a look at how properties are stored at some point... but not in this
thread. :-)

-John

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Received on Mon Nov 28 13:09:59 2005

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