1. A computer based method executed by one or more processors, the method comprising: receiving a search query, which includes at least a first phrase and a second phrase, at a server that is in communication with an index server system storing a plurality of posting lists, at least some of the posting lists being associated with a phrase and including document identifiers for documents containing the phrase, and wherein the document identifiers in at least some posting lists are partitioned based on a relevance score that indicates a respective document's relevance to the phrase of the posting list, such that a first portion of the posting list contains document identifiers of documents with a higher relevance score than documents identified in a second portion of the posting list; responsive to the first phrase having a partitioned posting list and the second phrase lacking a partitioned posting list: intersecting the first portion of the posting list of the first phrase with the posting list of the second phrase to generate a first set of common documents, and intersecting the second portion of the posting list of the first phrase with the posting list of the second phrase to generate a second set of common documents; and ranking the documents in the combination of the first set of common documents and the second set of common documents.