3. The method of claim 2 , wherein a maximum quantity of documents is stored in the primary index.
2. The method of claim 1 , further comprising for at least a phrase of the identified phrases: selectively partitioning the posting list for the phrase into at least a first portion including identifiers of higher ranked documents and a second portion including identifiers of lesser ranked documents, the partitioning being based on a relevance score for a document identified in the posting list indicating the document's relevance to the phrase; storing the first portion in a primary index on the assigned index server; and storing the second portion in a secondary index on the assigned index server.