On Fri, Sep 9, 2011 at 9:28 AM, Carlos Martín Nieto <cmn@xxxxxxxx> wrote:
> On Fri, 2011-09-09 at 09:04 -0500, neubyr wrote:
>> On Fri, Sep 9, 2011 at 3:23 AM, Carlos Martín Nieto <cmn@xxxxxxxx> wrote:
>> > On Thu, 2011-09-08 at 21:37 -0500, neubyr wrote:
>> >> I have a test git repository with just two files in it. One of the
>> >> file in it has a set of two lines that is repeated n times.
>> >> e.g.:
>> >> {{{
>> >> $ for i in {1..5}; do cat ./lexico.txt >> lexico1.txt && cat
>> >> ./lexico.txt >> lexico1.txt && mv ./lexico1.txt ./lexico.txt; done
>> >> }}}
>> >>
>> >
>> > So you've just created some data that can be compressed quite
>> > efficiently.
>> >
>> >> I ran above command few times and performed commit after each run. Now
>> >> disk usage of this repository directory is mentioned below. The 419M
>> >> is working directory size and 2.7M is git repository/database size.
>> >>
>> >> {{{
>> >> $ du -h -d 1 .
>> >> 2.7M ./.git
>> >> 419M .
>> >>
>> >> }}}
>> >>
>> >> Is it because of the compression performed by git before storing data
>> >> (or before sending commit)??
>> >>
>> >
>> > Yes. Git stores its objects (the commit, the snapshot of the files,
>> > etc.) compressed. When these objects are stored in a pack, the size can
>> > be further reduced by storing some objects as deltas which describe the
>> > difference between itself and some other object in the object-db.
>> >
>>
>> Does git store deltas for some files? I thought it uses snapshots
>> (exact copy of staged files) only.
>
> Yes and no. The data model for git is to always store snapshots, and it
> always expects to have the full files available. In a packfile, however,
> in order to save space, some objects are stored as deltas to other
> objects in the same file.
>
> http://progit.org/book/ch9-4.html
>
Excellent.. That explains compression and deltas really well. Thanks again..
--
neuby.r
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