15. A computer system comprising: a storage subsystem configured to store a plurality of document indexes; and a processor coupled to the storage subsystem, the processor being configured to: extract feature information from each of a plurality of documents; define an upper limit for each of a plurality of size parameters for the plurality of document indexes, wherein the plurality of size parameters measure a size of each of the plurality of document indexes; and for at least a first one of the documents: select one of the document indexes as a destination index for the first document based on the feature information extracted from the first document, a set of current values of the size parameters for at least one of the indexes, and the upper limits for the size parameters for the at least one of the indexes; store a searchable representation of the first document in the destination index; and update the size parameters of the destination index based on the feature information for the first document.
16. The computer system of claim 15 wherein the size parameters include at least one parameter from a group consisting of a number of documents in the index, a number of tokens in the index, and a total size of the documents in the index.