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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 19:09:13 CET

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.

:)

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Received on Sat Feb 26 19:12:49 2005

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