1. A method, comprising: allocating respective storage space for multiple versions of each of multiple items of data; making multiple data changes to said multiple items of data where more than one of said items of data is changed multiple times, wherein, changes made to a same item of data have respective transaction identifiers such that a previous change to said same item of data is recognizable as having been made earlier than a later change to said same item of data through analysis of the previous and later changes' respective transaction identifiers, and wherein, changes made to said same item of data are kept so as to create different kept versions of said same item of data, and wherein, storage space needed to keep all of said different kept versions exceeds storage space allocated for said same item of data's multiple versions, said method therefore further including writing a newest version of said same item of data over an oldest version of said same item of data; flushing said items of data from a cache to a non volatile storage; marking said flushing of said items of data as a consistent point of said multiple items of data including assigning a global transaction identifier to said items of data; making additional changes to some but not all of said items of data after said flushing and keeping versions thereof, wherein, said changes to some but not all of said items of data have associated transaction identifiers that are recognizable as being made after said assignment of said global transaction identifier, and, recording on a list respective transaction identifiers for said changes made to some but not all of said items of data in a list; experiencing a crash before a next global transaction identifier is assigned for said items of data; and, in response to said crash, referring to said list to remove said versions thereof so as to restore said set of data items to said consistent point such that said versions thereof are not recognized.