Patent ID: 8806160

Claim:
A computer system comprising: a data storage medium; an overlay table; a mapping table organized as a plurality of levels, each level of the plurality of levels comprising one or more mapping table entries, where each of the plurality of entries comprises a tuple including a key; and a data storage controller coupled to the data storage medium; wherein in response to detecting a flattening condition, the data storage controller is configured to: identify a group of two or more levels of the plurality of levels which are logically adjacent in time; create a new level in the plurality of levels; insert one or more first records stored within the group into the new level, in response to detecting each of the one or more first records stores a unique key among keys stored within the group; and utilize a filtering condition to determine which of the first records are inserted into the new level, wherein the filtering condition comprises a validity of a given record as determined by the overlay table.