Yeah, I definitely considered using Redis too; I'd be able to leverage web UI for even stuff like adding/removing users from buckets. How are you handling with persistence? I presume backing up the dump.rdb file frequently? I'd be a shame to lose any of the data (though I'm probably being overly paranoid)

Using a combo of the append-only file[1] and a redis slave[2] you'll get about the best durability one can ask for in today's world (assuming you're aware of the gotchas with regard to expiring keys — an edge case).

[1] http://code.google.com/p/redis/wiki/AppendOnlyFileHowto [2] http://code.google.com/p/redis/wiki/ReplicationHowto

We were already using Redis and had an existing backup plan. Though if you're using Redis solely for feature rollout, you can likely get away with it failing gracefully in case the server is down.

We are using Redis as well. The C code is small, compilable anywhere, and has very small memory footprint when started fresh.

Redis has replaced Sphinx as our tag indexer (thanks to its ordered sort) for more than 2 months now. It has never been down.

Backup procedure is the same as our MySQL's, tgz the .rdb file to S3 daily.