1. A computer-implemented method comprising: assigning each phrase identified in a document collection a phrase number based on frequency of occurrence of the phrase in the document collection, wherein each indexed document has a document identifier; creating a phrase-sharded index for a search engine by, for each identified phrase: assigning the phrase to a server of a plurality of index servers based on a hash of the assigned phrase number, and storing a posting list of identifiers of documents of the document collection that contain the phrase on the assigned index server; identifying, using the index, documents responsive to a search query; and providing information about the identified documents to a requestor of the search query.