"Scale Out" is not Scalability

MySql, and innodb in particular, don't scale.  Don't plan to run a boatload of concurrent transactions against your MySql db.  I'm hoping things are better in 5.1, but they are dismal in 4.1.

There's just way too much "semaphore" contention.  Too many global mutex locks blocking threads that really aren't stepping on each other.  Too many global mutexes held way too long. Disk i/o done by a thread holding a mutex!

MySql AB claims their product scales.  Their proscribed technique is "scale out".  But their "scale out" scheme is really a workaround for the fact their product doesn't scale.

There's a reason folks pay big bucks for Oracle Enterprise.  Meanwhile, us entrepreneurial types trying to compute on the cheap have to grin and bear it.