Q4M (http://q4m.31tools.com) is a high-performance message queue that works as a pluggable storage engine of MySQL, used by Mixi (Japan's largest SNS provider) and Cybozu Labs (for running Pathtraq, one of the nation's largest web access stats service), etc. The presentation will cover from the design principles of Q4M, to how it is used to modularize, stabilize, and extend the web services.