1. A computer program product comprising a computer-readable storage medium tangibly storing instructions that, when executed by a data processing apparatus that comprises a programmable processor, cause the data processing apparatus to perform operations comprising: receiving a request to change a record in a database; determining that a copy of the record exists in one or more of a main index, a first delta index, and a second delta index of the database; invalidating the copy of the record; and generating a delta dictionary record in either the first delta index or the second delta index, the generating occurring in the first delta index when the first delta index is not being merged with the main index and in the second delta index when the first delta index is being merged with the main index, the delta dictionary record reflecting the requested change.