Don't call FindCommit for raw blobs
Repository#blob_at
can accept a reference or a SHA, so we don't need
to find the commit for the reference, we can just pass it straight
through.
We also make sure that Repository#blob_at
doesn't try to do anything
fancy with a README unless the file could be a README.
Calling FindCommit a lot can make Gitaly very sad: gitaly#3319 (closed) See the comments at gitlab-com/gl-infra/scalability#661 (comment 450955781) for more details.
To test this locally, you can use the performance bar. First, open your browser inspector (while logged in), then load a file like http://localhost:3000/root/wget2/-/raw/master/todo.txt. You can take the X-Request-Id header, click '+' in the performance bar in another tab, and then see the results:
For a file that could be a README, we have some special casing code, so we will still call FindCommit there: