Methods, systems and apparatus, including computer program products, for propagating data across shards of a database system are described. According to one method, a first request that includes instructions to place a second request in a queue of a second shard is placed in a queue of a first database shard, and the change is committed to the records of the first shard. A queue processor polling the queue fetches and dispatches the first request, placing the second request in a queue of a second database shard. The second request includes instructions for making the change to the second shard. A queue processor of the second database shard polls the queue of the second database, fetches the second request, and dispatches it to make the change on the second database shard.