1. A database engine implemented in a computer system that is coupled to a database store that provides for the storage of a database table, said database engine being operative in responsive to database query requests relative to said database table to return a current sequence of data tuples corresponding to a predetermined database query request, said database engine comprising: a write-store structure that provides for the storage of data tuple updates pending application to said database table, the data tuple updates being stored in a positional delta tree data structure having a tree node and one or more leaf nodes that stores differential updates; a computer implemented merge scan processor, coupled to said write-store structure, operative to retrieve from said database table an initial sequence of data tuples responsive to said predetermined database query request, said merge scan processor being further dynamically operative to selectively merge said data tuple updates with said initial sequence of data tuples using the positional delta tree data structure to provide said current sequence of data tuples; an update processor, coupled to said write-store structure, said update processor operative, in response to database update requests relative to said database table, to receive and store differential data tuples in said write-store structure, wherein said update processor, within a defined transaction, is operative to allocate a transaction-store to receive and store differential data tuples, said update processor being further operative to transfer differential data tuples stored in said transaction-store to said write-store structure conditionally on commit of said defined transaction; and a query processor operative to allocate a snapshot write-store structure with respect to said defined transaction wherein said snapshot write-store structure contains a copy of the differential data tuples existing in said write-store structure at the initiation of said defined transaction, wherein database query requests relative to said database table complete relative to said snapshot write-store structure in preference to said write-store structure.