tailieunhanh - Software Fault Tolerance Techniques and Implementation phần 5

Thời gian dự phòng thường bao gồm lặp đi lặp lại một thực hiện bằng cách sử dụng cùng một phần mềm và các tài nguyên phần cứng có liên quan trong việc thực hiện không thành công ban đầu,. Điều này là điển hình của các chương trình phục hồi phần cứng lạc hậu (roll-back). Các chương trình lạc hậu phục hồi được sử dụng để phục hồi | 126 Software Fault Tolerance Techniques and Implementation an executive that handles orchestrating and synchronizing the technique . distributing the inputs as shown one or more additional variants versions of the algorithm program and a DM. The versions are different variants providing an incremental sort. For versions 1 and 2 a quicksort and bubble sort are used respectively. Version 3 is the original incremental sort. Also note the design of the DM. It is straightforward to compare result values if those values are individual numbers or strings or other basic types . How do we compare a list of values Must all entries in all or a majority of the lists be the same for success Or can we compare each entry in the result lists separately Since the result of our sort is an ordered list we can check each entry against the entries in the same position in the other result lists. If we designate the result in this example as Tij where i 1 2 3 up to n 3 versions and j 1 2 .6 up to k 6 items in the result set then our DM performs the following tests Z A r j r2j rĩj where j 1 k If the Tij are equal for a specific j then the result for that entry in the list is I j randomly selected since they are all equal . If they are not all equal for a specific j do any two entries for a specific j match That is does I j r2j OR I j r3j OR r2j r3j where j 1 k If a match is found the matching value is selected as the result for that position in the list. If there is no match that is r j r2j r3y then there is no correct result for that entry designated by 0. Now let s step through the example. Upon entry to NVP the executive performs the following it formats calls to the n 3 versions and through those calls distributes the inputs to the versions. The input set is 8 7 13 4 17 44 . Each version Vi i 1 2 3 executes. The results of the version executions Tij i 1 . n j 1 . k are gathered by the executive and submitted to the DM. Team-Fly Design Diverse Software Fault Tolerance Techniques 127