Question

According to this:

It is important to note that this is very different from most SCM
systems that you may be familiar with. Subversion, CVS, Perforce,
Mercurial and the like all use Delta Storage systems – they store
the differences between one commit and the next. Git does not do
this – it stores a snapshot of what all the files in your project
look like in this tree structure each time you commit. This is a
very important concept to understand when using Git.

Yet when I run git show $SHA1ofCommitObject…

commit 4405aa474fff8247607d0bf599e054173da84113
Author: Joe Smoe <[e-mail]>
Date:   Tue May 1 08:48:21 2012 -0500

    First commit

diff --git a/index.html b/index.html
new file mode 100644
index 0000000..de8b69b
--- /dev/null
+++ b/index.html
@@ -0,0 +1 @@
+<h1>Hello World!</h1>
diff --git a/interests/chess.html b/interests/chess.html
new file mode 100644
index 0000000..e5be7dd
--- /dev/null
+++ b/interests/chess.html
@@ -0,0 +1 @@
+Did you see on Slashdot that King's Gambit accepted is solved! <a href="http://game

… it outputs the diff of the commit with the previous commits. I know that git doesn’t store diffs in blob objects, but does it store diffs in commit objects? Or is git show dynamically calculating the diff?

Answer 1

No, commit objects in git don’t contain diffs – instead, each commit object contains a hash of the tree, which recursively and completely defines the content of the source tree at that commit. There’s a nice explanation in the git community book of what goes into blob objects, tree objects and commit objects .

All the diffs that are shown to you by git’s tools are calculated on demand from the complete content of files.