http://docs.drizzle.org/mysql_differences.htmlDrizzle appears to be a drop-in replacement DB that it is Mysql compatible (being forked from Mysql 6), but is a much, much slimmed down version. Despite this, it appears to have retained all the functionality required by the popular php/mysql apps I'd deploy.
I tried a few times on building this, but get continuously rebuked by boost libraries, for which I can see cause lots of issues in extension building due to incompatible versioning. Either that, or the extensive requirement of boost libraries I'm somehow not satisfying.
(source:
http://docs.drizzle.org/installing/from_source.html#dependencies)
If it provides a mem footprint smaller than the 24MB+ one I get from mysqld, I'd consider this a huge win.