So, if you're bypassing most of the bits of an RDBMS, what do you actually gain? Is the InnoDB storage engine that much superior compared to other products? Or is it about the management and admin features, e.g. sharding, replication?
I don't have much experience with mysql, but I can think of at least of few reasons why it would make sense to me. First, you get a relatively solid, well known storage backend, with > decade of bug fixes. Writing things reliably to disk is surprisingly hard. Then, everybody knows mysql, it is packaged and tested in any OS you would use for production. Finally, there are a huge number of tools, wrappers, etc... the chance of using a language without mysql is near 0, for example, whereas you often need to roll your own, or use a very new one (untested) for nosql solutions.
Sorry about the awkwardly worded question. What I meant is, what do you actually get from using MySQL? I can understand that a lot of people aren't willing to make a switch to some dedicated KVS, but going through all that effort would seem to require the same amount of time, if not more. So there has to be something about using MySQL that makes it worth using even in this stripped down configuration.
I think the idea is that you store your data in a relational model and access it using SQL. But for things that need to be looked up a lot, and very quickly, rather than tagging on a KV store in front of MySQL, use the method he describes instead.
This way you don't end up duplicating the cache, it is shared between the two different types of lookups. You also don't end up with data inconsistancies. And yet you get the speed that a dedicated KV store would have got you anyway.
Convenience of the complex queries. If you need anything more than a simple key-value access, you'll in fact need to implement the query engine yourself if you decide to use NoSQL.
Note that the author specifically mentioned that they use HandlerSocket for fast key retrievals and SQL for complex queries, and both methods work together on the very same database.
