System and method for selectively searching partitions of a database

A computer implemented document search system comprising multiple computing devices each having at least one processor and memory, said document search system, comprising:

• a first document index:
• a second document index comprising a plurality of document index partitions, each partition comprising a subset of the second document index, each document index partition comprising a plurality of document index sub-partitions, each document index sub-partition configured to map terms to documents;
• a plurality of partition indexes, each corresponding to a respective document index partition, each partition index mapping a specified term to a subset of the document index sub-partitions of the corresponding document index partition;
• wherein the plurality of partition indexes together correspond to all partitions of the second document index;
• a plurality of balancers, each respective balancer configured to receive a search query having a set of terms, comprising one or more terms, to search a respective partition index of the plurality of partition indexes so as to identify a subset of the document index sub-partitions that contain the set of terms, and to direct the search query to only the identified subset of the document index sub-partitions;
• wherein the plurality of balancers operate in parallel;
• wherein the plurality of balancers direct each search query to all of the partition indexes in the plurality of partition indexes;
• and
• a mixer for obtaining first search results from a first document index for documents that satisfy the search query, for determining whether first search results satisfy predetermined criteria, and when the first search results do not satisfy the predetermined criteria, for performing additional operations, including sending the search query to all of the plurality of balancers and receiving and collating search results from the plurality of balancers to produce second search results.