19. The system of claim 18 , wherein the one or more processors are further configured to execute the stored instructions to cause the system to: store a plurality of shards of different phrase posting lists on a first index server; store a 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, order the shard according to document identifiers of the documents included in the shard.
18. An indexing system for indexing documents in a document collection, the system comprising: a plurality of index servers; one or more memory devices configured store executable instructions; and one or more processors configured to execute the stored instructions to cause the system to: determine a phrase posting list associated with a first phrase, the phrase posting list identifying documents of the document collection associated with the first phrase; divide the phrase posting list for the first phrase into a plurality of shards, each shard identifying a subset of the documents identified by the posting list; and store each shard of the phrase posting list for the first phrase on a corresponding index server; determine a phrase posting list associated with a second phrase, the phrase posting list identifying a number of documents of the document collection having at least one occurrence of the second phrase; divide the phrase posting list for the second phrase into a plurality of shards, each shard identifying a subset of the plurality of the documents identified by the posting list; and store each shard of the phrase posting list for the second phrase on a corresponding index server, wherein shards of the phrase posting list for the first phrase and shards of the phrase posting list for the second phrase, which identify the same document, are stored on the same index server.