Geert Bosch wrote:
On Dec 14, 2006, at 10:06, Andreas Ericsson wrote:
It wouldn't work for this particular case though. In our distribution
repository we have ~300 bzip2 compressed tarballs with an average size
of 3MiB. 240 of those are between 2.5 and 4 MiB, so they don't
drastically differ, but neither do they delta well.
One option would be to add some sort of config option to skip
attempting deltas of files with a certain suffix. That way we could
just tell it to ignore *.gz,*.tgz,*.bz2 and everything would work just
as it does today, but a lot faster.
Such special magic based on filenames is always a bad idea. Tomorrow
somebody
comes with .zip files (oh, and of course .ZIP), then it's .jpg's other
compressed content. In the end git will be doing lots of magic and still
perform
badly on unknown compressed content.
Hence config option. People can tell git to skip trying to delta
whatever they want. For this particular mothership repo, we only ever
work against it when we're at the office, meaning resulting datasize is
not an issue, but data computation can be a real bottle-neck.
There is a very simple way of detecting compressed files: just look at the
size of the compressed blob and compare against the size of the expanded
blob.
If the compressed blob has a non-trivial size which is close to the
expanded
size, assume the file is not interesting as source or target for deltas.
Example:
if (compressed_size > expanded_size / 4 * 3 + 1024) {
/* don't try to deltify if blob doesn't compress well */
return ...;
}
Many compression algorithms generate similar output for similar input.
Most source-code projects change relatively little between releases, so
they *could* delta well, it's just that in our repo they don't.
--
Andreas Ericsson andreas.ericsson@xxxxxx
OP5 AB www.op5.se
Tel: +46 8-230225 Fax: +46 8-230231
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