1. An indexing system comprising: one or more processors; one or more electronic memories to provide random access memory; one or more mass storage devices to provide persistent data storage; and one or more indexing routines to, when executed by the one or more processors: create and manage an index data structure comprising nodes that include key-value/reference pairs, the index data structure including, in the one or more electronic memories, a plurality of the index data structure nodes and, for each of one or more of the plurality of the index data structure nodes, a respective additional reference to a respective other component of the index data structure stored in the one or more electronic memories; transfer the plurality of the index data structure nodes from the one or more electronic memories to the one or more mass-storage devices; and remove, from the index data structure, the one or more respective additional references when transferring the plurality of index data structure nodes.