Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for receiving from a plurality of publishers messages of a first channel of a plurality of distinct channels wherein each channel comprises an ordered plurality of messages, storing messages of the first channel in one or more first buffers according to the order, each first buffer having a respective time-to-live, for one or more connections, determining a respective sampling rate based on a data type of the first channel and a determined latency of the connection, receiving from a subscriber through a first connection a request for messages of the first channel, selecting messages in the first buffers according to the order and the sampling rate, and sending the selected messages using the first connection to the subscriber according to the order.
