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Re: Delta directions (was Re: delta combiner sloooooooowwwwww)

From: Greg Hudson <ghudson_at_MIT.EDU>
Date: 2005-02-10 19:22:21 CET

I hadn't read part of the "make blame even faster" thread when I sent
this. Having read it, I have one addendum:

On Thu, 2005-02-10 at 13:08, Greg Hudson wrote:
> (Obviously not before 2.0, but I'm not sure if we can
> realize any of these benefits before 2.0.)

As people pointed out in that other thread, we can realize the "faster
delta combiner" benefit before 2.0, and it may be worth changing to
xdelta in 1.2 in order to do so. My biggest concern is that FSFS
repositories with very shallow file histories may become significantly
larger, since we will lose all self-compression. Perhaps we can
continue using vdelta for self-compression in FSFS? I'm not sure how
much of the speed win (if any) we'd be giving up by doing that.

At any rate, the more desirable end state is to ditch svndiff and switch
to a format which doesn't even allow random access, and to have a
compression layer on the output of the delta routine. That would let us
recapture most or all of the space efficiency and would let us use
deltas in other ways. But getting to that end state is much more
difficult than simply changing our delta algorithm from vdelta to

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Received on Thu Feb 10 19:23:59 2005

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