about the delta technique used in Bazaar

Bo Chen chen at chenirvine.org
Tue Jul 2 19:03:12 UTC 2013

Thanks. Martin.

I am also curious on some more specific aspects:
1) in this group, it only includes different versions of the same file, or
can include versions from other files?
2) how to choose the base for delta?

I don't know python, and cannot read the code you provided.



On Tue, Jul 2, 2013 at 2:07 AM, Martin Pool <mbp at sourcefrog.net> wrote:

> bzr's compression is in the 'groupcompress<http://bazaar.launchpad.net/~bzr-pqm/bzr/bzr.dev/view/head:/bzrlib/groupcompress.py>'
> module. Briefly, this stores a set of related file versions together, and
> then does gzip entropy compression across the whole set of them. This gives
> a good compression, including compression across files, while bounding the
> amount of data that has to be read to unpack any single versions. Files are
> recompressed over time in to larger groups (up to a certain ceiling) so
> that older versions get more compression and slightly longer access time.
> On 2 July 2013 15:08, Bo Chen <chen at chenirvine.org> wrote:
>> version control systems usually use delta techniques to optimize the
>> storage of the repository. Can anyone tell me what delta technique
>> Bazaar uses? Reverse delta? forward delta? others?
>> Thanks.
>> Bo
> --
> Martin
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