How can I recover my Git repository for a “missing tree” error?

Question

We are using Gerrit for our Git repository. On a project that has been active for several months, we are suddenly unable to push any changes. When we execute git pus

Answer 1

When we get this, I can almost always fix it with a git gc:

git gc --aggressive --prune=now

back up your git repo first!

Answer 2

Technically this answer's a little late, but what worked for me was to create a patch for the changeset I was trying to push, recloned the repository to another disk location, Applied the patch, recommitted, and pushed.