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Re: [Gnu-arch-users] Re: situations where cached revisions are not so go

From: Jason McCarty
Subject: Re: [Gnu-arch-users] Re: situations where cached revisions are not so good
Date: Wed, 24 Sep 2003 15:03:14 -0400
User-agent: Mutt/1.3.28i

I wrote:
> The space requirements of this aren't as bad as they sound; if you chunk
> your patches in sets of N, then your entire archive will be about
> SIZE * N / (N - 1), where SIZE is the size of the archive without any
> cached items. In other words, less than double the original size. I
> think that makes summary-deltas a viable (and possibly superior)
> alternative to cachedrevs.

Bah, my math is wrong here. Assuming that each revision is mostly
independent of the others (not fully true, I know), the space
requirements would be roughly SIZE*(1 + log base N of R), where R is the
number of revisions. That's not nearly as good, even when summary-deltas
are smaller than the sum of the revisions they span.

I'm not sure anymore that summary-deltas would be a significant
improvement over downloading all the revisions needed after a cachedrev.
Tla should instead try to minimize the downloading requirements, by
finding the closest (in bytes, forwards or backwards) pristine, library
revision, or cachedrev (including the size of the cachedrev) to the
desired revision, and patching from there. That logic might be on the
server or the client, I suppose.


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