At MySQLCamp, mention was made of a few Google internal patches to MySQL4 to improve replication and IO throughput on InnoDB (Mark Callaghan, ex-Oracle, did the InnoDB work).
The good news is that Google has just released them.
The license is GPL, so we’ll see what MySQL AB can do with them as their code is dual-licensed (GPL and commercial).
Hopefully this will prod Yahoo! into releasing more patches for Open Source software they use. I’ve heard that in 2006 it was tough for employees to get permission to release MySQL patches into the open.
Google releases patches that enhance the manageability and reliability of MySQL
List of MySQL4 Patches