18. The computer program product of claim 17 , wherein the computer readable program when executed by the processor on the computer causes the computer to perform: maintaining a persistent, transactionally recoverable structure that stores the virtual-index-epoch map.
18. The computer program product of claim 17 , wherein the computer readable program when executed by the processor on the computer causes the computer to perform: maintaining a persistent, transactionally recoverable structure that stores the virtual-index-epoch map. 20. The computer program product of claim 18 , wherein the computer readable program when executed by the processor on the computer causes the computer to perform: maintaining the virtual-index-epoch map by at least one of creating and deleting virtual-index-epoch numbers from the virtual-index-epoch map.