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Rebase doesn't work that way, though [0]. It first extracts the 3 versions (2 leafs and their common ancestor) and then does a diff & patch. This allows git to

by tlb 6y ago

Rebase doesn't work that way, though [0]. It first extracts the 3 versions (2 leafs and their common ancestor) and then does a diff & patch. This allows git to store the deltas between versions in the most efficient way on disk, while also letting it use contextual diffs to minimize the chance of spurious merge conflicts. Patching algorithms have various heuristics that make sense for programming languages, like special treatment for lines with only changes in whitespace. (Edited to add:) also, minimal diff algorithms have to do a lot of work to detect large blocks of text being moved around. This is part of what made Subversion, which used the same diff algorithm for storage compression and merging, painfully slow. [0] https://git-scm.com/book/en/v2/Git-Branching-Rebasing https://git-scm.com/book/en/v2/Git-Branching-Rebasing

hibbelig 6y ago
Here is the paragraph that describes what rebase does: > This operation works by going to the common ancestor of the two branches (the one you’re on and the one you’re rebasing onto), getting the diff introduced by each commit of the branch you’re on, saving those diffs to temporary files, resetting the current branch to the same commit as the branch you are rebasing onto, and finally applying each change in turn. Is "applying the diff to a different parent" not a good way to describe this?
- tlb 6y ago
  You're using the word 'diff' for 2 different things: - an efficient way to store 2 very similar files - the minimal set of changes made by a programmer to a file. Subversion uses the same diff algorithm for these 2 functions, which is why people conflate them. But git uses different algorithms. The first one (which it calls deltas) are optimized for speed and compression ratio. The second set of algorithms (you can choose from a few, some of which are better at identifying rearrangements of large blocks of text) are optimized for merging 2 programmer's changes without conflicts.

by tlb 6y ago

hibbelig 6y ago

Here is the paragraph that describes what rebase does: > This operation works by going to the common ancestor of the two branches (the one you’re on and the one you’re rebasing onto), getting the diff introduced by each commit of the branch you’re on, saving those diffs to temporary files, resetting the current branch to the same commit as the branch you are rebasing onto, and finally applying each change in turn. Is "applying the diff to a different parent" not a good way to describe this?

tlb 6y ago
You're using the word 'diff' for 2 different things: - an efficient way to store 2 very similar files - the minimal set of changes made by a programmer to a file. Subversion uses the same diff algorithm for these 2 functions, which is why people conflate them. But git uses different algorithms. The first one (which it calls deltas) are optimized for speed and compression ratio. The second set of algorithms (you can choose from a few, some of which are better at identifying rearrangements of large blocks of text) are optimized for merging 2 programmer's changes without conflicts.