Middleware for Heterogeneous and Distributed Information Systems Exercise Sheet 1

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1 AG Heterogene Informationssysteme Prof. Dr.-Ing. Stefan Deßloch Fachbereich Informatik Technische Universität Kaiserslautern Middleware for Heterogeneous and Distributed Information Systems Exercise Sheet 1 Wednesday, November 03, :45 to 15:15 Room ACID Properties The following definition was taken from the book Transaction Processing Concepts and Techniques by Jim Gray and Andreas Reuter (page 6). Atomicity A transaction s changes to the state are atomic: either all happen or none happen. These changes include database changes, messages, and actions on transducers. Consistency A transaction is a correct transformation of the state. The action taken as a group do not violate any of the integrity constraints associated with the state. This requires that the transaction be a correct program. Isolation Even though transactions execute concurrently, it appears to each transaction, T, that others executed either before T or after T, but not both. Durability Once transaction completes successfully (commits), its change to the state survives failure. Middleware for Heterogeneous and Distributed Information Systems 1

2 Distributed Transactions 1. Both agents commit successfully. Log: Begin Log : Commit Log : End Middleware for Heterogeneous and Distributed Information Systems 2

3 2. One of the agents encounters an internal error within the prepare phase that prevents the transaction from completing successfully. Log : Begin Failure Enter state ABORTED Log:Aborted FAILED Log: Abort ABORT ABORT Log : Aborted Log: End Middleware for Heterogeneous and Distributed Information Systems 3

4 3. One of the agents crashes within the prepare phase. Log: Begin Log: Prepared Crash Timeout Log : Abort ABORT Log: Aborted Restart Log: Aborted FAILED Log : End Middleware for Heterogeneous and Distributed Information Systems 4

5 4. One of the agents crashes within the commit/abort phase after both agents voted commit. Log: Begin Log : Commit Crash Restart tart Log : End Middleware for Heterogeneous and Distributed Information Systems 5

6 5. The coordinator crashes after the prepare phase has been successfully completed. Log: Begin Log : Commit Crash The agents have to wait until the coordinator is available again. The agents CAN- NOT abort the transaction locally, after having sent in the prepare phase! Log : End Middleware for Heterogeneous and Distributed Information Systems 6

7 Distributed Information Systems 1. reservelectureroom( ) cataloglecture( ) Transaction routing provides location transparency. However, it does not support distributed transactions. One of the above operations may fail while the other succeeds. In consequence the overall system may be left in an inconsistent state. 2. begintransaction(); try { reservelectureroom( ); cataloglecture( ); catch (RoomOccupiedException e) { rollback(); System.err.println( ); catch (LectureCollisionException e) { rollback(); System.err.println( ); commit(); 3. connect to LectureCatalogue connect to LectureRoomDatabase INSERT INTO lecture VALUES (:lectureid, :title, :lecturer, :timeslot, :description) INSERT INTO reservation VALUES (:roomid, :timeslot, :lectureid) commit 4. connect to FDBMS INSERT INTO lecture VALUES (:lectureid, :title, :lecturer, :timeslot, :description) INSERT INTO reservation VALUES (:roomid, :timeslot, :lectureid) commit Middleware for Heterogeneous and Distributed Information Systems 7

8 5.Distribution alternative 3: exec sql declare c1 cursorfor SELECT lectureid FROM lecture WHERE lecturer = :lecturer_var; exec sql declarec2cursorfor SELECT roomid FROM reservation WHERE lectureid = :lectureid_var; /* set value of lecturer_var */ exec sql open c1; while(sqlcode == 0) { exec sql fetch c1 INTO :lectureid_var; exec sql openc2; while(sqlcode == 0) { exec sql fetch from C2 into:roomid; /* process results */ exec sql closec2; exec sql close c1; 5.Distribution alternative 4: connect to FDBMS SELECT r.roomid FROM lecture l, reservation r WHERE l.lecturer = :lecturer AND r.lectureid = l.lectureid Middleware for Heterogeneous and Distributed Information Systems 8