How is the global write lock "fixable" without a major rewrite of the codebase?

Like the article suggested, it would be one thing if they did it for transaction support. In reality, from looking at the code, it seems like the global write lock came from not wanting to solve the hard problems other people are solving.

A major rewrite of the core engine is exactly what's needed. Sounds like a fun project. If they don't do it, someone else will.

Adoption is hard to replace. Modifying API's is really hard. Rewriting a core engine? Reasonable and in this case probably necessary given the issues.

There are lots of people here who could replace that core engine and someone should if the MongoDB guys can't.

Meh, if your other option is to use PostgreSQL and get row level locks, a db level lock is still a fail.

And here's a great post that provides some insight on how much effort has been put in by RDBMS vendors to handle locking:

http://stackoverflow.com/a/872808