Message compression in scalable messaging system

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for receiving from a plurality of publisher clients a plurality of messages, each message being for a particular channel of a plurality of distinct channels wherein each channel comprises an ordered plurality of messages, encoding each message based on a particular dictionary, storing encoded messages in one or more respective buffers according to the order, each buffer having a respective time-to-live and residing on a respective node, retrieving encoded messages for the particular channel from respective buffers having time-to-lives that have not expired and according to the order, decoding each retrieved message based on the particular dictionary, and sending the decoded messages to a plurality of subscriber clients.