Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for assigning channels in a messaging system. An example method includes: providing a plurality of channels, wherein each channel includes an ordered plurality of messages; assigning each channel to a channel bucket to form a plurality of channel buckets, wherein each channel bucket includes at least two channels from the plurality of channels; and assigning each channel bucket to a node selected from a plurality of nodes, wherein the node includes one or more buffers for storing messages according to the order from the channel buckets of the node.