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diff --git a/Documentation/gitfaq.txt b/Documentation/gitfaq.txt index 9cd7a592ac..51d305d58f 100644 --- a/Documentation/gitfaq.txt +++ b/Documentation/gitfaq.txt @@ -241,6 +241,38 @@ How do I know if I want to do a fetch or a pull?:: ignore the upstream changes. A pull consists of a fetch followed immediately by either a merge or rebase. See linkgit:git-pull[1]. +Merging and Rebasing +-------------------- + +[[long-running-squash-merge]] +What kinds of problems can occur when merging long-lived branches with squash merges?:: + In general, there are a variety of problems that can occur when using squash + merges to merge two branches multiple times. These can include seeing extra + commits in `git log` output, with a GUI, or when using the `...` notation to + express a range, as well as the possibility of needing to re-resolve conflicts + again and again. ++ +When Git does a normal merge between two branches, it considers exactly three +points: the two branches and a third commit, called the _merge base_, which is +usually the common ancestor of the commits. The result of the merge is the sum +of the changes between the merge base and each head. When you merge two +branches with a regular merge commit, this results in a new commit which will +end up as a merge base when they're merged again, because there is now a new +common ancestor. Git doesn't have to consider changes that occurred before the +merge base, so you don't have to re-resolve any conflicts you resolved before. ++ +When you perform a squash merge, a merge commit isn't created; instead, the +changes from one side are applied as a regular commit to the other side. This +means that the merge base for these branches won't have changed, and so when Git +goes to perform its next merge, it considers all of the changes that it +considered the last time plus the new changes. That means any conflicts may +need to be re-resolved. Similarly, anything using the `...` notation in `git +diff`, `git log`, or a GUI will result in showing all of the changes since the +original merge base. ++ +As a consequence, if you want to merge two long-lived branches repeatedly, it's +best to always use a regular merge commit. + Hooks ----- |