40. A non-transitory computer readable storage medium storing one or more programs, the one or more programs comprising instructions which, when executed by a computer system having one or more processors and memory, cause the computer system to: receive a query, the query comprising one or more tokens; identify, in a compressed sequence of tokens that includes a plurality of cluster subsequences, each cluster subsequence corresponding to a respective cluster of documents, one or more cluster subsequences that each include at least one of the query tokens, wherein the compressed sequence of tokens includes respective cluster subsequences from which duplicate sequences of tokens have been elided; for at least one respective cluster subsequence of the identified cluster subsequences, identify one or more documents within the respective cluster subsequence that satisfy the query; and return the identified documents as matches to the query.
40. A non-transitory computer readable storage medium storing one or more programs, the one or more programs comprising instructions which, when executed by a computer system having one or more processors and memory, cause the computer system to: receive a query, the query comprising one or more tokens; identify, in a compressed sequence of tokens that includes a plurality of cluster subsequences, each cluster subsequence corresponding to a respective cluster of documents, one or more cluster subsequences that each include at least one of the query tokens, wherein the compressed sequence of tokens includes respective cluster subsequences from which duplicate sequences of tokens have been elided; for at least one respective cluster subsequence of the identified cluster subsequences, identify one or more documents within the respective cluster subsequence that satisfy the query; and return the identified documents as matches to the query. 41. The computer readable storage medium of claim 40 , wherein the query includes a Boolean AND expression that includes two or more of the query tokens; and identifying cluster subsequences comprises identifying in the compressed sequence of tokens one or more cluster subsequences that each include all of the query tokens.