1. One or more computer storage media storing computer useable instructions that, when used by a computing device, cause the computing device to perform a method comprising: receiving a search query comprising one or more terms; analyzing the search query to identify one or more atoms from the one or more terms; querying a search index using the one or more atoms identified from the search query, wherein the search index comprises a plurality of postings lists, each posting list corresponding with an atom and including a plurality of postings, wherein each posting within a given posting list corresponding with the atom identifies a document containing the atom and a rank representing a significance of the atom for the document, wherein at least one posting list is divided into a plurality of tiers ordered based on rank; and wherein querying the search index comprises determining whether to perform additional processing, to identify a plurality of documents, based on comparing a combined rank of a first set of documents identified after a first tier with a calculated combined rank of the first set of documents of the first tier and one or more documents of at least a second tier; identifying the plurality of documents from querying the search index based on the plurality of tiers ordered based on rank and the postings within each of the plurality of tiers; and providing a plurality of search results for presentation to an end user based on the plurality of documents identified by querying the search index.