Back in April I wrote that MySQL 5.5.4 is Very Exciting and couldn’t wait to start running it in production. Now here we are several months later and are using 5.5.4-m3 on all the slaves in what is arguably our most visible (and one of the busiest) user-facing cluster. Along the way we deployed some new hardware (Fusion-IO) but not a complete replacement. Some boxes are Fusion-io, some local RAID, and some SAN. We have too many eggs for any one basket.
We also converted table to the Barracuda format in InnoDB, dropped an index or two, converted some important columns to BIGINT UNSIGNED and enabled 2:1 compression for the table that has big chunks of text in it. Aside from a few false starts with the Barracuda conversion and compression, things went pretty well. Coming from 5.0 (skipping 5.1 entirely) we had some my.cnf work to do to take advantage of all the new InnoDB tuning (especially on the boxes with Fusion-IO cards and more memory). Hopefully switching the master goes smoothly too.
Needless to say, we have some very good and dedicated folks working behind the scenes to make it all happen (hi, Josh). Most of my involvement was initial testing, prodding, schema changes, and finding my.cnf options for the InnoDB tuning.