At the moment, there are two big features in the works in MySQL optimizer – Subquery optimizations and Batched Key Access. While the former is a part of MySQL 6.0, I wrote about it here in my blog, and so forth, the latter was in nearly stealth mode until a couple of weeks ago.
That’s no longer the case:
- Batched Key Access source code is now published as mysql-6.0-bka-preview tree.
- Igor Babaev, the author of the feature, gave a talk about Batched Key Access at MySQL User Conference, and the slides are available here.
- There is now Batched Key Access page on forge.mysql.com which a semi-official feature homepage which describes how you can get source, binaries, etc
If you’re developing any kind of “remote” storage engine or are using MySQL in a data warehousing application where disk IO is the bottleneck, I recommend to take a look.
Sergei Petrunia's blog 