A non-static collection of machines self-organizes into a linear communication orbit. A server has sent a data unit to a subset of machines in the linear communication orbit. A first machine receives a plurality of shards of the data unit from an upstream neighbor of the first machine in the linear communication orbit and sends the plurality of shards of the data unit to a downstream neighbor of the first machine in the linear communication orbit. The first machine selects and maintains a subset of the plurality of shards of the data unit in a local cache of the first machine according to a data caching method. The first machine selects the subset of the plurality of shards it maintains independently of whether the subset of the plurality of shards are maintained locally by the upstream neighbor and the downstream neighbor of the first machine in the linear communication orbit.