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Re: [PATCH] FSFS speedup (was: Re: Making blame even faster)

From: Daniel Berlin <dberlin_at_dberlin.org>
Date: 2005-02-26 19:19:26 CET

On Sat, 2005-02-26 at 13:09 -0500, Daniel Berlin wrote:
> On Sat, 2005-02-26 at 12:43 -0500, Greg Hudson wrote:
> > On Tue, 2005-02-22 at 20:24, Daniel Berlin wrote:
> > > On Mon, 2005-02-21 at 23:03 -0500, Greg Hudson wrote:
> > > > On Mon, 2005-02-21 at 20:37, Daniel Berlin wrote:
> > > > > ChangeLog is > SVN_DELTA_WINDOW_SIZE when deltified, and you only
> > > > > auto-expand the first window
> > > >
> > > > That doesn't agree with my reading of Peter's change. It looks like he
> > > > auto-expands all windows of the last rep.
> > > >
> > > > (Something is obviously wrong, but I'm not convinced this is it.)
> > >
> > > Fair enough.
> > > I've put the repo in question (it's about 1/8th the total revisions of
> > > our changelog) at http://www.toolchain.org/~dberlin/repo.dump.bz2
> >
> > As far as I can tell, what's wrong is the basic premise of this whole
> > optimization. A chain of deltas with no "copy from target" operations
> > does not necessarily avoid copy_source_ops().
>
> This is true from the current composition standpoint, however, with no
> overlaps, composition is trivial. Much more trivial than what we do now
> (we shouldn't need the search_offset_index portion, because we can just
> sort the offsets once and walk both windows at the same time).
>
> Also, the idea was not to avoid copy_source_ops entirely in the current
> scheme, it was to avoid quadratic behavior we got from copy_source_ops,
> which it should.
>
Just to clarify further, i believe my original message was incorrect,
because we should still see copy_source_ops activity (just not quadratic
behavior).

IOW, nothing to see here at the moment, move along :)

--Dan

PS that'll teach me to write emails while in the midst of stressing over
a bar exam.

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Received on Sat Feb 26 19:23:17 2005

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