I've been searching for a way to speed up my analysis runs, and Redis's philosophy of keeping everything in RAM looks very promising for my uses. As I mentioned previously, I hit a lot of speed-bumps trying to get it working with PHP, but I finally got up and running and ran some tests. The results were good, faster than using the purely disk-based Tokyo Tyrant setup I have been relying on.
The only niggling issue was that I knew from Tokyo that Unix file (aka domain) sockets have a lot less overhead and help performance compared to TCP sockets, even using localhost. Since the interface is almost identical, I decided to dive in and spend a couple of hours patching my copy of Redis 1.02 to support file sockets. The files I've changed are available at http://web.mailana.com/labs/redis_diff.zip.
My initial results using the redis-benchmark app that ships with the code show a noticeable performance boost across the board, sometimes up to 2x. Since this is an artificial benchmark it's unlikely to be quite this dramatic in real-world situations, but with Tokyo 30%-50% increases in speed were common.
I hope these changes will get merged into newer versions of Redis, it's a comparatively small change to get a big performance boost in situations when the client and server are on the same machine.