Re: Weird growth in packfile during initial push

Nicolas Pitre [off-list ref] writes:

quoted

$ git push origin master:master
Initialized empty Git repository in /var/gitroot/exp/gentoo-x86.git/
Counting objects: 4969800, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (1217809/1217809), done.
Writing objects: 100% (4969800/4969800), 810.56 MiB | 21608 KiB/s, done.
Total 4969800 (delta 3735812), reused 4969800 (delta 3735812)

Here we know for sure that all objects were directly reused, so no 
attempt at recompressing them was done.  The only thing that 
pack-objects might do in this case in addition to directly streaming the 
existing pack is to convert delta object headers from OFS_DELTA to 
REF_DELTA.

quoted

$ ls -la /var/gitroot/exp/gentoo-x86.git/objects/pack
total 966876
drwxr-xr-x 2 git git      4096 Apr 14 08:43 .
drwxr-xr-x 4 git git      4096 Apr 14 08:35 ..
-r--r--r-- 1 git git 139155472 Apr 14 08:43 pack-f805bb448f864becfeac9c7f8a8ac2ef90c26787.idx
-r--r--r-- 1 git git 849936308 Apr 14 08:43 pack-f805bb448f864becfeac9c7f8a8ac2ef90c26787.pack

Let's see if my theory stands:

	849936308 - 786336481 = 63599827
	63599827 / 3735812 = 17.02

Hence an average difference of 17 bytes per delta.  Given that REF_DELTA 
objects have a 20-byte SHA1 base reference which is replaced with a 
variable length encoding of a pack offset in the OFS_DELTA case, we're 
talking about 2.98 bytes for that offset encoding which feels about 
right.

[...]

And the code matches this theory as well.  Can you try this patch if you 
have a chance?

Is there any progress on this?

I think you did a veryclear analysis.  8% size reduction is not only
unignorable but use of delta offset should also help runtime efficiency,
right?