How Gitaly fits into GitLab: Creating Git commits on behalf of Git users

A 1-hour training video for contributors new to GitLab and Gitaly.

Demonstrate how usually Git hooks are run by
git-receive-pack, but sometimes by gitaly-ruby. Deep dive into
UserCommitFiles: where do those hooks actually get run? A look at
UserMerge. How does Gitaly make merge commits. A look at the
implementation of the special feature where users are not allowed
push to a branch, but are allowed to merge into it.

Recorded 2019-03-21