c99fb58909
Thanks Valentin Haenel for a test case showing how non-fast-forward merges could result in an ongoing pull/merge/push cycle. While the git-annex branch is fast-forwarded, git-annex's index file is still updated using the union merge strategy as before. There's no other way to update the index that would be any faster. It is possible that a union merge and a fast-forward result in different file contents: Files should have the same lines, but a union merge may change their order. If this happens, the next commit made to the git-annex branch will have some unnecessary changes to line orders, but the consistency of data should be preserved. Note that when the journal contains changes, a fast-forward is never attempted, which is fine, because committing those changes would be vanishingly unlikely to leave the git-annex branch at a commit that already exists in one of the remotes. The real difficulty is handling the case where multiple remotes have all changed. git-annex does find the best (ie, newest) one and fast forwards to it. If the remotes are diverged, no fast-forward is done at all. It would be possible to pick one, fast forward to it, and make a merge commit to the rest, I see no benefit to adding that complexity. Determining the best of N changed remotes requires N*2+1 calls to git-log, but these are fast git-log calls, and N is typically small. Also, typically some or all of the remote refs will be the same, and git-log is not called to compare those. In the real world I expect this will almost always add only 1 git-log call to the merge process. (Which already makes N anyway.) |
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