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Re: Subversion branch deltification policy is more space-hungry than CVS

From: Edmund Horner <chrysophylax_at_chrysophylax.cjb.net>
Date: 2004-05-21 13:02:11 CEST

Max Bowsher wrote:

> Subversion stores more fulltexts than CVS, for the same history, if branching is used at all.
>
> This becomes very visible when people convert from CVS to subversion, and their repositories increase significantly in size.
>
> CVS stores 1 fulltext per file.
>
> SVN stores 1 fulltext per file *plus* an additional fulltext for every branch on which a file is modified.
>
>
> This is a tradeoff of space vs. checkout speed which is different to that made by CVS, and needs to be carefully considered, as it
> may well dissuade people from switching from CVS to SVN.

The trick is to do the deltas the other way round, isn't it? I read it
in some file somewhere, but I couldn't easily find it in notes/ or
libsvn_fs_base/notes/. But I think it's also what libsvn_fs_fs does:

First revision is stored as plaintext. Succeeding revisions are stored
as deltas against earlier ones.

The tradeoff is that it's faster to commit (I think), but slower to read
new revisions (particularly HEAD). But that can be improved by a cache,
can't it?

Anyway without thinking about it too hard, I think it would also improve
the space usage of branches.

Hopefully someone can figure out where it's described properly by
whichever you you core devs thought of it.

Edmund.

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Received on Fri May 21 13:03:26 2004

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