11. A computer-implemented method comprising: receiving a query for information from the document collection, wherein the query includes a first 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 different index server of the plurality of index servers; serving a response to the query, wherein the response is based on information in the phrase posting list associated with the first phrase; and storing a plurality of shards of different phrase posting lists on a first index server; storing plurality of shards of different phrase posting lists on a second index server; and within each of the first and second index servers, for each shard of a phrase posting list, ordering the shard according to document identifiers of the documents included in the shard.
11. A computer-implemented method comprising: receiving a query for information from the document collection, wherein the query includes a first 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 different index server of the plurality of index servers; serving a response to the query, wherein the response is based on information in the phrase posting list associated with the first phrase; and storing a plurality of shards of different phrase posting lists on a first index server; storing plurality of shards of different phrase posting lists on a second index server; and within each of the first and second index servers, for each shard of a phrase posting list, ordering the shard according to document identifiers of the documents included in the shard. 14. The method of claim 11 , further comprising storing shards of the phrase posting list for the first phrase in duplicate on different index servers.