I started playing around with the idea of storing references directly in Git. Exploiting the GITLINK tree entry, we can associate a name to any SHA-1. By storing all references in a single tree, atomic transactions are possible. Its a simple compare-and-swap of a single 40 byte SHA-1. This of course leads to a bootstrapping problem, where do we store the 40 byte SHA-1? For this example its just $GIT_DIR/refs/txn/committed as a classical loose reference. I posted code for this to JGit (sorry): https://git.eclipse.org/r/62970 Configuration: [core] repositoryformatversion = 1 [extensions] refsBackendType = RefTree For example, recent git.git has a structure like this: $ git ls-tree -r refs/txn/committed 120000 blob 22e42fc826b437033ca444e09368f53a0b169322 ..HEAD 160000 commit 1ff88560c8d22bcdb528a6629239d638f927cb96 heads/maint 160000 commit f3adf457e046f92f039353762a78dcb3afb2cb13 heads/master 160000 commit 5ee9e94ccfede68f0c386c497dd85c017efa22d6 heads/next 160000 commit d3835d54cffb16c4362979a5be3ba9958eab4116 heads/pu 160000 commit 68a0f56b615b61afdbd86be01a3ca63dca70edc0 heads/todo ... 160000 commit 17f9f635c101aef03874e1de1d8d0322187494b3 tags/v2.6.0 160000 commit 5bebb9057df8287684c763c59c67f25f16884ef6 tags/v2.6.0-rc0 160000 commit 16ffa6443e279a9b3b63d7a2bebeb07833506010 tags/v2.6.0-rc0^{} 160000 commit bbdca2a7bd942e1d3ce517b48e6229b99f7d7b2b tags/v2.6.0-rc1 160000 commit 689efb737a7b46351850eefdfa57d2ce232011fb tags/v2.6.0-rc1^{} 160000 commit 7b269a793392ee3d71ecddac88a8ad63497cbc4d tags/v2.6.0-rc2 160000 commit 45733fa93f287fbc04d6a6a3f5a39cc852c5cf50 tags/v2.6.0-rc2^{} 160000 commit 27df6e2585060add45b32bbd46f6e92ef79d069b tags/v2.6.0-rc3 160000 commit 8d530c4d64ffcc853889f7b385f554d53db375ed tags/v2.6.0-rc3^{} 160000 commit be08dee9738eaaa0423885ed189c2b6ad8368cf0 tags/v2.6.0^{} Tags are stored twice, to cache the peel information for network advertisements. Packing the tree by itself is smaller than packed-refs, which is uncompressed: -rw-r----- 1 shawn me 60K Dec 17 12:43 packed-refs -r--r----- 1 shawn me 1.2K Dec 17 12:56 R-5533*.idx -r--r----- 1 shawn me 28K Dec 17 12:56 R-5533*.pack By exploiting Git to store Git, we get a reflog for free: $ git log -p refs/txn/committed -1 commit f7ec5ceeba6ca87fa112b3af70d8ac17364045f7 Author: anonymous <anonymous@localhost> Date: Thu Dec 17 12:53:39 2015 -0800 push diff --git a/heads/tmp2 b/heads/tmp2 deleted file mode 160000 index f3adf45..0000000 --- a/heads/tmp2 +++ /dev/null @@ -1 +0,0 @@ -Subproject commit f3adf457e046f92f039353762a78dcb3afb2cb13 :) -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html