First, how big is a brand new empty Git directory (.git)?



$ git init
Initialized empty Git repository in /home/dave/tmp/foo/.git/

$ du -sb .git
64828	.git

 
(The du options are: s to summarize and b to display bytes.)


Now I’m going to make a bunch of tiny files in directories with a pair of nested shell loops:



$ for d in {1..5};do
    mkdir $d;
    for f in {1..50};do
        echo foo > $d/$f;
    done;
done



Now I have 250 files in 5 directories containing the string "foo":



$ ls
1  2  3  4  5
$ cat 2/45
foo

 

$ git add .
$ git commit -m 'initial commit'



Let’s see how big .git is now:
 
The commit has added about 47 Kb to the initial blank repo.


Aside: I calculated this in the geekiest way I could think of, using the standard Unix command dc, the arbitrary precicision reverse-polish notation desk calculator (note that 'p' is the print command so we can see the result!):



$ dc -e '112468 64828 - p'
47640



Now I’ll make one tiny change to one file and commit it:



$ echo bar > 1/1
$ git commit -am 'changed 1/1'

$ du -sb .git
129613
$ dc -e '129613 112468 - p'
17145



So that’s 17 Kb to store about 3 bytes of changes to my repo.


Where is that weight coming from?


I’m gonna do another little commit. Here’s what it looks like before:



$ du -b .git
4096	.git/objects/info
4096	.git/objects/pack
4115	.git/objects/25
4155	.git/objects/7b
4225	.git/objects/af
4115	.git/objects/57
4271	.git/objects/07
4177	.git/objects/61
4255	.git/objects/bb
4299	.git/objects/a8
45900	.git/objects
4336	.git/info
4096	.git/refs/tags
4137	.git/refs/heads
12329	.git/refs
4096	.git/branches
4411	.git/logs/refs/heads
8507	.git/logs/refs
12918	.git/logs
27538	.git/hooks
129613	.git



Then I modify file 1/1 again to contain the string 'baz' and commit that.
 

4096	.git/objects/info
4096	.git/objects/pack
4115	.git/objects/25
4253	.git/objects/81 <-- new 4 Kb
4155	.git/objects/7b
4225	.git/objects/af
4115	.git/objects/57
4271	.git/objects/07
4177	.git/objects/61
4302	.git/objects/fc <-- new 4 Kb
4255	.git/objects/bb
4115	.git/objects/76 <-- new 4 Kb
4299	.git/objects/a8
4177	.git/objects/92 <-- new 4 Kb
62747	.git/objects
4336	.git/info
4096	.git/refs/tags
4137	.git/refs/heads
12329	.git/refs
4096	.git/branches
4561	.git/logs/refs/heads <-- added 0.1 Kb
8657	.git/logs/refs
13218	.git/logs
27538	.git/hooks
146759	.git



That’s 4 new objects for a single-file commit.
 
Although these files are all zlib compressed data, I figured out that git show will show the value of any object by hash identifier, not just commits!


So to view these objects, I did:



$ ls .git/objects/81
b1a9d27494b40679d612b96bb6acaac83afa9c
$ git show 81b1a9d27494b40679d612b96bb6acaac83afa9c

 


81…​ is my actual commit


fc…​ is the tree file for the changed directory 1., listing all of the files in that directory (1 through 50).


76…​ is the actual contents of file 1/1 (which is now the string 'baz')


92…​ is another tree for the root directory of the repo




That makes sense. There’s a commit, two trees, and one file.