Exciting news from LCA miniconfs
Florian Haas gave a talk yesterday at the HA miniconf to present Flashcache, a project that was spawned from Facebook and their desire to squeeze more performance out of their databases.
The basic concept is to use any SSD device as a cache in front of slower rotational media. This is similar to commercial products such as LSI’s Cachecade, but implemented as a linux device-mapper module (so you wouldn’t be able to boot from such a setup, but that’s unlikely to be a real concern).
One of the nice things about Flashcache is that it’s presented as a plain block device. As well as making for a robust and understandable system, a practical upshot of this is that you can also replicate your cache with DRBD. In large HA database setups, this would mitigate a lot of the cache warmup penalty that you suffer after a reboot or failover event.
Flashcache is also fairly configurable, and exposes a lot of stuff through procfs rather than being a black box.
At the moment you have to build it as an out-of-tree module, so of course it’s not the kind of thing we’ll be rushing into production any time soon. Based on what we’ve seen in the past, I reckon there’s a good chance we’ll see Flashcache in mainline in a year or two if there’s a concerted push on development.