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hugo/content/posts/2023-09-06-git-showcase.md

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+---
+lastmod: "2023-09-06T13:51:00.0000000+01:00"
+author: patrick
+categories:
+- programming
+date: "2023-09-06T13:51:00Z"
+title: Notes for a Git fireside chat
+summary: "A syllabus for a fireside chat to give at work, on Git"
+---
+
+This is simply an outline, with no actual content.
+
+# How Git works
+
+* Recommendation to read Pro Git
+* Fundamental model: the object database
+  * Blobs, trees, tags, commits
+* Extra metadata
+  * Branches
+  * Lightweight tags
+  * HEAD (and other symbolic refs)
+  * Remotes
+* Mention of performance optimisations such as packfiles
+* Merge algorithms
+  * recursive
+  * ort
+  * ours
+* Useful commands
+  * `git rev-parse`
+  * `git merge-base`
+  * `git symbolic-ref`
+  * `git clone --depth=1`
+  * `git commit --amend`
+  * `git grep` (although ripgrep is generally faster anyway)
+  * `git log -p` (for patch) and `-S function_name`
+  * `git blame`
+* Brief mention of what a submodule is
+* Brief mention of what `git rebase` is
+* How-tos
+  * Stacked PRs in a squash-merge-to-`main` world
+* Case studies
+  * `$INTERNAL_WORKSPACE_TOOL push-files`
+  * my internal Git-related dotfiles
+  * [git-appraise](https://github.com/google/git-appraise)
+
+
+# Problems with Git, and why Pijul is interesting
+
+## Merging
+
+Git works on snapshots => merging is impossible in principle.
+Here's the textbook example:
+
+Start:
+```
+A
+B
+```
+
+Branch 1:
+```
+A
+X
+B
+```
+
+Branch 2:
+```
+G
+A
+B
+```
+then
+```
+A
+B
+G
+A
+B
+```
+
+When merging branch 1 and branch 2, the snapshot-based merge algorithm can't know which AB pair the X was added in between, so it must choose arbitrarily.
+
+
+## Conflicts
+
+Conflicts are not modelled at all: a conflict is only a property of the working tree, and you can't "commit it".
+That means *you can never tell Git how to resolve a conflict* in such a way that it can reliably resolve the same conflict again in the future.
+(`git rerere` is a hack that in my experience frequently does not do the right thing.)