Re: git repack command on larger pack file

From: Sivakumar Selvam <gerritcode@gmail.com>
Date: Oct 27, 2015, 02:04 UTC
Message-ID: <loom.20151027T025257-333@post.gmane.org>
In-Reply-To: <xmqqziz6hzom.fsf@gitster.mtv.corp.google.com>

Junio C Hamano <gitster <at> pobox.com> writes:

Show 52 quoted lines

> 
> Junio C Hamano <gitster <at> pobox.com> writes:
> 
> > Sivakumar Selvam <gerritcode <at> gmail.com> writes:
> >
> >> ... So
> >> I thought of splitting the pack file into 4 GB chunks.
> > ...
> > Hmmm, what is "this issue"?  I do not see anything surprising.
> 
> While the explanation might have been enlightening, the knowledge
> conveyed by the explanation by itself would not be of much practical
> use, and enlightment without practical use is never fun.
> 
> So let's do another tangent that may be more useful.
> 
> In many repositories, older parts of the history often hold the bulk
> of objects that do not change, and it is wasteful to repack them
> over and over.  If your project is at around v40.0 today, and it was
> at around v36.0 6 months ago, for example, you may want to pack
> everything that happened before v36.0 into a single pack just once,
> pack them really well, and have your "repack" not touch that old
> part of the history.
> 
>   $ git rev-list --objects v36.0 |
>     git pack-objects --window=200 --depth=128 pack
> 
> would produce such a pack [*1*]
> 
> The standard output from the above pipeline will give you a 40-hex
> string (e.g. 51c472761b4690a331c02c90ec364e47cca1b3ac, call it
> $HEX), and in the current directory you will find two files,
> pack-$HEX.pack and pack-$HEX.idx.
> 
> You can then do this:
> 
>   $ echo "v36.0 with W/D 200/128" >pack-$HEX.keep
>   $ mv pack-$HEX.* .git/objects/pack/.
>   $ git repack -a -d
> 
> A pack that has an accompanying .keep file is excempt from
> repacking, so once you do this, your future "git repack" will only
> repack objects that are not in the kept packs.
> 
> [Footnote]
> 
> *1* I won't say 200/128 gives you a good pack; you would need to
> experiment.  In general, larger depth will result in smaller pack
> but it will result in bigger overhead while you use the repository
> every day.  Larger window will spend a lot of cycles while packing,
> but will result in a smaller pack.
>

Hi Junio,

   When I finished git repacking, I found 12 pack files with each 4 GB and
the total size is 48 GB. Again I ran the same git repack command by just
removing only --max-pack-size= parameter, the size of the single pack file
is 66 GB.

git repack -A -b -d -q --depth=50 --window=10 abc.git

Now, I see the total size of the single abc.git has become 66 GB. Initially
it was 34 GB, After using  --max-pack-size=4g it become 48 GB. When we
remove the --max-pack-size=4g parameter and tried to create a single pack
file now it become 66 GB.
   
Looks like once we do git repack with multiple pack files, we can't revert
back to the original size.

Thanks, Sivakumar Selvam.