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0 pointschrismorgan3y ago0 comments

There may be some extra trigger that causes it to go beyond seven for everything, I don’t know (never worked on a repository anywhere near that large), but there’s certainly still at least some form of collision logic in there (and this is why I said what I said, because I’ve used lucky_commit enough to experience it):

  $ git init x
  Initialized empty Git repository in /tmp/x/.git/

  $ cd x

  $ git commit --allow-empty -m one
  [master (root-commit) 4144321] one

  $ git log --oneline
  4144321 (HEAD -> master) one

  $ lucky_commit

  $ git log --oneline
  0000000 (HEAD -> master) one

  $ git commit --amend --no-edit --reset-author --allow-empty
  [master 3430e13] one

  $ git log --oneline
  3430e13 (HEAD -> master) one

  $ lucky_commit

  $ git log --oneline
  0000000f (HEAD -> master) one

  $ git reflog --oneline
  0000000f (HEAD -> master) HEAD@{0}: amend with lucky_commit
  3430e13 HEAD@{1}: commit (amend): one
  00000005 HEAD@{2}: amend with lucky_commit
  4144321 HEAD@{3}: commit (initial): one

  $ git reflog expire --expire=now --all

  $ git reflog --oneline

  $ git log --oneline
  0000000f (HEAD -> master) one

  $ git gc --aggressive --prune=now
  Enumerating objects: 2, done.
  Counting objects: 100% (2/2), done.
  Writing objects: 100% (2/2), done.
  Total 2 (delta 0), reused 0 (delta 0), pack-reused 0

  $ git log --oneline
  0000000 (HEAD -> master) one

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1 comments · 1 top-level

avar3y ago

Yes, there's also a collision check, but it's not truncating to 7 characters and adding as needed to get past collisions. Rather it's truncating to N and then adding as needed. N=7 for a new repository, but it'll relatively quickly bump that to 8, then 9 etc

You don't need a very large repository to start bumping it up to 8 etc. E.g. my local redis.git is 9, some local few-thousand commit (partially automated) that I've only ever added to are at 8 etc.

This changed in v2.11 released in late 2016[1], but because the observable default on a new repository is 7 the "it's 7 unless collisions" has persisted in various places online.

All of which is to say that if you brute-force the first commit to be 0000001..., it'll start being displayed as <that><x>, where <x> is a random 0..9a..f character, unless you brute force to 8, 9 etc.

1. https://github.com/git/git/commit/e6c587c733b4634030b353f402...

j / k navigate · click thread line to collapse

$ git init x Initialized empty Git repository in /tmp/x/.git/ $ cd x $ git commit --allow-empty -m one [master (root-commit) 4144321] one $ git log --oneline 4144321 (HEAD -> master) one $ lucky_commit $ git log --oneline 0000000 (HEAD -> master) one $ git commit --amend --no-edit --reset-author --allow-empty [master 3430e13] one $ git log --oneline 3430e13 (HEAD -> master) one $ lucky_commit $ git log --oneline 0000000f (HEAD -> master) one $ git reflog --oneline 0000000f (HEAD -> master) HEAD@{0}: amend with lucky_commit 3430e13 HEAD@{1}: commit (amend): one 00000005 HEAD@{2}: amend with lucky_commit 4144321 HEAD@{3}: commit (initial): one $ git reflog expire --expire=now --all $ git reflog --oneline $ git log --oneline 0000000f (HEAD -> master) one $ git gc --aggressive --prune=now Enumerating objects: 2, done. Counting objects: 100% (2/2), done. Writing objects: 100% (2/2), done. Total 2 (delta 0), reused 0 (delta 0), pack-reused 0 $ git log --oneline 0000000 (HEAD -> master) one