42. The method of claim 40 , further comprising storing shards of the phrase posting list for the first phrase in duplicate on different index servers.
40. A computer-implemented method comprising: receiving a query for information from the document collection, wherein the query includes a first phrase and a second phrase; accessing a plurality of index servers to retrieve identifiers of documents on a phrase posting list associated with the first phrase, wherein the phrase posting list identifies documents of the document collection associated with the first phrase, and is divided into a plurality of shards, each shard identifying a subset of the plurality of the documents identified by the posting list, and each different shard being stored on a corresponding index server of the plurality of different index servers; accessing a plurality of the index servers to retrieve identifiers of documents on a phrase posting list associated with the second phrase, wherein the phrase posting list identifies documents of the document collection associated with the second phrase, and is divided into a plurality of shards, each shard identifying a subset of the plurality of the documents identified by the posting list, and each shard being stored on a corresponding index server of the plurality of index servers; and serving a response to the query, wherein the response is based on information in the phrase posting list associated with the first phrase and is based on information in the phrase posting list associated with the second phrase.