[gbog]

Genuine question: github is built upon git, which is a rock solid system for storing dataand in these reports we read that github relies a lot on MySQL, so... Did the github guys ponder using git as their data store? Just an example, in git one can add comments on commits, would it be possible to use it for the github comment function? Or maybe it is?

[holman]

Generally, Git will be way too slow for that. Git is typically our bottleneck, since you're dealing with so much overhead and disk access to perform functions.

Databases are best for, well, performing relational queries. In the case of commenting on a commit, if you store them only in the repository it becomes non-trivial to ask "show me all of the comments by this user" unless you have an intermediary cache layer (in which case you're back where you started).

[gbog]

Thanks for answering. Tell me if I'm wrong but MySQL would be behind a caching layer anyway, so the choice would be between cached git or cached git + mysql.

In git, logging commits on a file from an author is also a kind of join, and it is surprisingly fast, so using git as a data store is a weird idea that I cannot take out of my head.