Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for processing sharded reservation queries for corresponding publisher data shards. Each publisher data shard stores a proper subset of impression records corresponding to a publisher site and a plurality of user identifiers. Each impression record includes user identifier data corresponding to a user identifier and time data specifying a time that an impression was delivered for the publisher site for the corresponding user identifier, and all impression records corresponding to the user identifiers are stored in the publisher data shard.

Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for selecting forecasted impressions randomly with respect to their impression times. For each randomly selected forecasted impression, a set of matching reservations are determined. The impression is assigned to one of the reservations based on satisfaction values associated with the reservations.