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Jini Transaction Part II

Jini Transaction Part II. Daniel Müller Marcel Ziswiler. Seminar Informations- & Kommunikationssysteme. Overview. ACID 2 Phase Commit Mahalo Jini Transaction & JavaSpaces References. Daniel M üller. Seminar Informations- & Kommunikationssysteme. ACID 2 Phase Commit Mahalo

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Jini Transaction Part II

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  1. Jini TransactionPart II Daniel Müller Marcel Ziswiler Seminar Informations- & Kommunikationssysteme

  2. Overview • ACID • 2 Phase Commit • Mahalo • Jini Transaction & JavaSpaces • References Daniel Müller Seminar Informations- & Kommunikationssysteme

  3. ACID 2 Phase Commit Mahalo Jini Transaction & JavaSpaces References ACID • Atomicity • Consistency • Isolation • Durability Daniel Müller Seminar Informations- & Kommunikationssysteme

  4. T = (a := a+5; => Two Phase Commit ACID Atomicity Consistency Isolation Durability Atomicity • All operations of a transaction occur or none of them! T = (a := a+5; b := b+3) Daniel Müller Seminar Informations- & Kommunikationssysteme

  5. ACID Atomicity Consistency Isolation Durability Consistency • Semantic • Not supported ! • Outside of the realm of the transaction itself • Transaction = Tool to allow consistency guarantees • Transaction = A guarantor of consistency Daniel Müller Seminar Informations- & Kommunikationssysteme

  6. ACID Atomicity Consistency Isolation Durability Isolation • Ongoing transactions should not affect each other • Not supported ! Daniel Müller Seminar Informations- & Kommunikationssysteme

  7. ACID Atomicity Consistency Isolation Durability Durability • The result should be persistent • Not supported ! • Durability is a commitment but • Not a guarantee ! • It depends on the application how durable data has to be Daniel Müller Seminar Informations- & Kommunikationssysteme

  8. ACID 2 Phase Commit Mahalo Jini Transaction & JavaSpaces References Two PhaseCommit • Problem • Transaction States • Client’s View • Participant’s View • Transaction Manager’s View • Exceptions • PrepareAndCommit Daniel Müller Seminar Informations- & Kommunikationssysteme

  9. Two Phase Commit Problem Transaction States Client’ View Participant’ s View Transaction Manager’s View Exceptions PrepareAndCommit Problem • Treat a transaction as a single atomic unit • All operations of the transaction succeed or fail • No partial failures • Two Phase Commit Protocol • Can be used in more than traditional transaction systems Daniel Müller Seminar Informations- & Kommunikationssysteme

  10. Two Phase Commit Problem Transaction States Client’ View Participant’ s View Transaction Manager’s View Exceptions PrepareAndCommit TransactionStates • Constants defined for the communication between managers & participants public interface TransactionConstants { int ACTIVE = 1; int VOTING = 2; int PREPARED = 3; int NOTCHANCHED = 4; int COMMITED = 5; int ABORTED = 6; } Daniel Müller Seminar Informations- & Kommunikationssysteme

  11. Two Phase Commit Problem Transaction States Client’ View Participant’ s View Transaction Manager’s View Exceptions PrepareAndCommit Client’sView I ACTIVE create returns otherwise commit VOTING COMMITED participant ABORTED abort cleanup ABORTED Daniel Müller Seminar Informations- & Kommunikationssysteme

  12. Client’sView II • create()  ACTIVE • commit()  VOTING • abort()  ABORTED • Cancel the lease ABORTED • Expire the lease ABORTED Daniel Müller Seminar Informations- & Kommunikationssysteme

  13. Two Phase Commit Problem Transaction States Client’ View Participant’ s View Transaction Manager’s View Exceptions PrepareAndCommit Participant’sView I ACTIVE NOTCHANGED join returns abort prepare cleanup VOTING ABORTED abort abort PREPARED commit COMMITED Daniel Müller Seminar Informations- & Kommunikationssysteme

  14. Participant’s View II • join()  ACTIVE • prepare()  VOTING • Decide to return one of the following states • NOTCHANGED: read-only (no changes in the state) • PREPARED: changes made & able to roll forward • ABORTED: changes made but can’t guarantee to roll forward Daniel Müller Seminar Informations- & Kommunikationssysteme

  15. Participant’s View III • PREPARED & commit()  COMMITED • abort()  ABORTED • request the state of the transaction manager int getState(long id);  Crash Recovery Daniel Müller Seminar Informations- & Kommunikationssysteme

  16. Two Phase Commit Problem Transaction States Client’ View Participant’ s View Transaction Manager’s View Exceptions PrepareAndCommit TransactionManager’s View I ACTIVE create returns commit otherwise VOTING COMMITED participant ABORTED or timeout abort ABORTED cleanup Daniel Müller Seminar Informations- & Kommunikationssysteme

  17. TransactionManager’s View II • create()  ACTIVE • commit()  VOTING • Invoke prepare() of all participants • One participant votes ABORTED  ABORTED • A participant votes NOTCHANGED  Dropped as participant • No one ABORTED & at least one PREPARED  COMMITED • abort() ABORTED • Lease cancelled  ABORTED • Lease expired  ABORTED Daniel Müller Seminar Informations- & Kommunikationssysteme

  18. Two Phase Commit Problem Transaction States Client’ View Participant’ s View Transaction Manager’s View Exceptions PrepareAndCommit Exceptions • UnknownTransactionException • Incorrect transaction ID • Transaction already cleaned up • CannotCommitException • Transaction already ABORTED or COMMITED • CannotAbortException • Transaction already COMMITED • TimeoutExpiredException • Wasn’t able to notify all participants in a given time Daniel Müller Seminar Informations- & Kommunikationssysteme

  19. Two Phase Commit Problem Transaction States Client’ View Participant’ s View Transaction Manager’s View Exceptions PrepareAndCommit prepareAndCommit I • Optimisation / Elimination of the VOTING state • Only one single participant • Only one single participant to prepare()and all others already returned NOTCHANGED Daniel Müller Seminar Informations- & Kommunikationssysteme

  20. prepareAndCommitII public int prepareAndCommit(TransactionManager mgr, long id) throws UnknownTransactionException, RemoteException { int result = prepare(mgr, id); if (result == PREPARED) { commit(mgr, id); result = COMMITED; } return result; } Daniel Müller Seminar Informations- & Kommunikationssysteme

  21. ACID 2 Phase Commit Mahalo Jini Transaction & JavaSpaces References Mahalo • Transaction engine in Sun’s distribution of Jini, as an implementation of a simple transaction manager • An activatable service; it means that it runs under the control of rmid (RMI daemon) Daniel Müller Seminar Informations- & Kommunikationssysteme

  22. ACID 2 Phase Commit Mahalo Jini Transaction & JavaSpaces References Jini Transactions& JavaSpaces • Problem • Example • Solution • Entries under a transaction • ACID revisited Daniel Müller Seminar Informations- & Kommunikationssysteme

  23. JavaSpaces Problem Example Solution Entries under a transaction ACID revisited Problem • Tool for dealing with partial failure • Transactions provide a means of enforcing consistency over a set of (one or more) space-based operations • Consistency: • bundle operations together • Either all complete or none of them Daniel Müller Seminar Informations- & Kommunikationssysteme

  24. JavaSpaces Problem Example Solution Entries under a transaction ACID revisited Example:Web Counter • Problem: Counter lost • Visit a web page • Applet takes a page count entry • Increments its value • Writes it back into the page Daniel Müller Seminar Informations- & Kommunikationssysteme

  25. JavaSpaces Problem Example Solution Entries under a transaction ACID revisited Solution • take & write under a Transaction • .. Transaction txn = trc.transaction; counter = space.take(tmp, txn, Long); counter.increment(); space.write(counter, txn, Lease); .. Daniel Müller Seminar Informations- & Kommunikationssysteme

  26. JavaSpaces Problem Example Solution Entries under a transaction ACID revisited Entries under a Transaction • write entry is only seen within the transaction until it commits • read a entry once read, cannot be taken afterwards, within the same transaction • readIfExists  If an entry is taken by another transaction then wait for its return • take removes en entry temporarily from the space Daniel Müller Seminar Informations- & Kommunikationssysteme

  27. JavaSpaces Problem Example Solution Entries under a transaction ACID revisited ACIDRevisited • Atomicity • Consistency • Isolation • Durability Daniel Müller Seminar Informations- & Kommunikationssysteme

  28. ACID Atomicity Consistency Isolation Durability Atomicity • Two Phase Commit • All operations occur ore non of them • Both: Counter was removed from and returned to the space • None: Counter was effectively never removed • Operations are read, write, take, notify Daniel Müller Seminar Informations- & Kommunikationssysteme

  29. ACID Atomicity Consistency Isolation Durability Consistency • Changes do not violate the correctness of the state within the space • Program / Algorithm has to be correct • take and write the counter • increment the value by one Daniel Müller Seminar Informations- & Kommunikationssysteme

  30. ACID Atomicity Consistency Isolation Durability Isolation • Two transactions should not affect each other • take removes the entry temporarily • Deadlock ? Daniel Müller Seminar Informations- & Kommunikationssysteme

  31. ACID Atomicity Consistency Isolation Durability Durability • After commit, changes to a space will survive failures • Problem of the space, not the transaction Daniel Müller Seminar Informations- & Kommunikationssysteme

  32. ACID 2 Phase Commit Mahalo Jini Transaction & JavaSpaces References References • Sun Inc., Jini Technology core platform specification, Version 1.1, Oct. 2000, http://www.sun.com/jini/specs/core1_1.pdf • Scott Oaks & Henry Wong, Jini in a Nutshell, O’Reilly, 2000, http://www.oreilly.com/catalog/jininut • Jan Newmarch, University of Canberra, http://pandonia.canberra.edu.au/java/jini/tutorial • Eric Freeman, Susanne Hupfer, Ken Arnold, JavaSpaces principles, patterns, and practice, Addison Wesley, 1999, http://204.179.152.61/book/0,3828,0201309556,00.html Daniel Müller Seminar Informations- & Kommunikationssysteme

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