- One of those meta-data items is "Parent Commit," so if you change one item in history, it changes the SHA-1 sum of all subsequent items (because at the very least they all need to be re-parented).
- All of the commit objects are stored under .git/objects.
- Branches are just files under .git/refs/ that contain the SHA-1 sum of the most recent commit on that branch. This is why they are called 'branch pointers.' That's basically all they are.
- If you have a history of 5 commits, and make a change to the initial commit, you now have 10 commits in your .git/ directory. Your (e.g.) 'master' branch will point to the most recent 'tree' of 5 commits. The other commits will still exist in .git/objects, but there will be no branches pointing them. You can use 'git reflog' to find them, or access them by their SHA-1 sum.
- Eventually 'git gc' (gc = garbage collect) will clean out the unreferenced commits, but this happens rarely if you don't explicitly run the command.
- When you 'git push,' you are only pushing branches to the remote repo, so commits that are stored locally, which are not referenced by one of those branches you are pushing, will not be pushed out. If you have commits that you don't want to end up in limbo like this, you should 'git tag' them or create a branch (e.g. 'archive/master-2013-12' that points to them).
Thanks for the help.
>One of those meta-data items is "Parent Commit," so if you change one item in history, it changes the SHA-1 sum of all subsequent items (because at the very least they all need to be re-parented).
What sequence of operations would change a history item in that way?
I've never looked at .git/logs, but it looks like that is used by the `git reflog` command. It's basically a history (or log) of every commit that a particular reference has pointed to[1]. For example, I cloned the git source code:
user@host ~/src/git % cat .git/logs/HEAD
0000000000000000000000000000000000000000 d7aced95cd681b761468635f8d2a8b82d7ed26fd First Last <user@example.com> 1387237920 -0500 clone: from https://github.com/git/git.git
user@host ~/src/git % git reflog
d7aced9 HEAD@{0}: clone: from https://github.com/git/git.git
~/src/git $ cat .git/HEAD
ref: refs/heads/master
~/src/git $ cat .git/refs/heads/master
d7aced95cd681b761468635f8d2a8b82d7ed26fd
> What are the SHA-1 sums of? Are they of the entire snapshot, or the delta? I went into objects/ and ran `sha1sum $objfile`, and the sum did not match the file name. So that remains obscure.
See: http://stackoverflow.com/questions/5290444/why-does-git-hash...
[1]: Since the local repository was created. This information does not sync between local and remote.