[mhodgson]

You could certainly try. I believe the core contributors moved away from the idea of pluggable backends once they realized the performance limitations. It still works great for some use cases, but I think the folks at GitHub quickly realized it wouldn't work for them.

[andrewstuart]

I'd be interested to hear more about the performance limitations.

My naive thoughts were that it would perform extremely well as I had thought that Postgres scales extremely well with multicore.

Is there anything I can read anywhere about such performance limitations? Am I correct in understanding that you found performance limitations - I assume when compared to file system?

Any pointers to info on where github tried this?

[mhodgson]

Once you understand how git works under the hood it's actually fairly easy to predict that performance will be poor. A simple checkout involves accessing 100s if not 1000s of objects. Also, you can't fetch these all at once because the objects you need to fetch are determined based on a nested tree. So you have to query the tree all the way down, getting each nested tree or blob based on the previous tree's contents. So ultimately you're doing 100s-1000s of queries for any given git command. Each query is fast, but even at 1-2 ms per query it adds up quickly.