Thanks Eric, MemSQL is pretty awesome but I can't really begin to consider it when:

1. Backing up your data is somehow an Enterprise feature?

2. No pricing anywhere on the site, which usually means:

2.1. Sales calls. Nothing I hate more in this world than sales calls.

2.2. $$$$$$$ (which is fine, but I like to know roughly how much $$$$$ before 2.1.)

As far as functional indices, I don't see that here:

http://docs.memsql.com/docs/create-index

What I mean is specifying a WHERE clause on the index.

If you are referring to indices on expressions, MemSQL definitely supports them. In MemSQL you do it by creating a computed column (http://docs.memsql.com/v5.0/docs/persistent-computed-columns) and creating an index over one of those. Computed columns turn out to give you a significant perf boost since you only have to run the expression once (at INSERT time), and never while executing a SELECT query or seeking in the index.