1. A computer-implemented method comprising: identifying a first query having first criteria, wherein the first criteria specifies one or more attributes of web page impressions; obtaining, from a database of web page impressions, a set of web page impressions that satisfy the first query; storing, as a pre-computed response to the first query, an identifier for each web page impression in the set; after storing the pre-computed response to the first query, receiving from a client device a second query having second criteria, wherein the second criteria specifies one or more attributes of web page impressions and wherein a number of second criteria is greater than a number of first criteria; generating a plurality of sub-queries from the second query, the plurality of sub-queries comprising (i) a first sub-query having the first criteria, and (ii) one or more other sub-queries, wherein each of the second criteria is represented in at least one of the plurality of sub-queries; obtaining a response for each of the one or more other sub-queries, from the database of web page impressions, wherein each response comprises identifiers of web page impressions satisfying criteria of the associated sub-query; comparing the pre-computed response to the first query and the responses to the one or more other sub-queries; and providing an answer to the client device based at least in part on said comparing the pre-computed response to the first query and the responses to the one or more other sub-queries.
1. A computer-implemented method comprising: identifying a first query having first criteria, wherein the first criteria specifies one or more attributes of web page impressions; obtaining, from a database of web page impressions, a set of web page impressions that satisfy the first query; storing, as a pre-computed response to the first query, an identifier for each web page impression in the set; after storing the pre-computed response to the first query, receiving from a client device a second query having second criteria, wherein the second criteria specifies one or more attributes of web page impressions and wherein a number of second criteria is greater than a number of first criteria; generating a plurality of sub-queries from the second query, the plurality of sub-queries comprising (i) a first sub-query having the first criteria, and (ii) one or more other sub-queries, wherein each of the second criteria is represented in at least one of the plurality of sub-queries; obtaining a response for each of the one or more other sub-queries, from the database of web page impressions, wherein each response comprises identifiers of web page impressions satisfying criteria of the associated sub-query; comparing the pre-computed response to the first query and the responses to the one or more other sub-queries; and providing an answer to the client device based at least in part on said comparing the pre-computed response to the first query and the responses to the one or more other sub-queries. 3. The computer-implemented method of claim 1 , further comprising storing a number of web page impressions satisfying the first query.