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WS-AtomicTransaction

WS-AtomicTransaction. Mark Little, Chief Architect Arjuna Technologies Ltd. Introduction. Coordinate agreement with ACID semantics A tomic, C onsistent, I solated, D urable Tried and trusted model Simple application model Synchronized state changes Correctness in the face of failures

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WS-AtomicTransaction

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  1. WS-AtomicTransaction Mark Little, Chief Architect Arjuna Technologies Ltd

  2. Introduction • Coordinate agreement with ACID semantics • Atomic, Consistent, Isolated, Durable • Tried and trusted model • Simple application model • Synchronized state changes • Correctness in the face of failures • Widespread adoption • Proven protocols

  3. Model Assumptions • Transactions are short lived • Resources isolated (locked) for duration • Coordinator availability • Connected and responsive • Timely failure recovery • Participants trust that the above are true

  4. But why…? • Web services are “for the internet” • B2B communication • Separate trust domains • Why WS-AT? • Two reasons • Interoperability • Heterogeneous systems • Ubiquity • Vision of WS-* scale down

  5. Core Scenarios • Some services require ACID properties - Tight coordination of mission critical state • Use with service-based resource managers • Example: Queue service • Use within datacenter • Controlled environment • Use with virtual datacenter • Between close partners • Contractual QOS

  6. Protocol • Defines WS-Coordination Coordination Type • http://schemas.xmlsoap.org/ws/2004/10/wsat • Activities are transactions • CreateCoordinationContext • Create transaction • Join transaction as subordinate • Register • Create subordinate enlistment • Three coordination protocols • Completion • Durable 2PC • Volatile 2PC • Simple message patterns • One-way messages • Correlation using WS-Addressing • Full state machines for 2PC

  7. The Actors • Completion Initiator (I) • Signals coordinator to complete a transaction • Can request commit or rollback • Coordinator (C) • Responsible for coordinating a single outcome • Drives 2PC with participants • Phase 1: Ensure all participants are prepared • Phase 2: Notify participants of outcome • Participants (P) • Can vote to abort • Can vote “prepared to commit” • Must honor coordinator’s commit decision

  8. WS-C and WS-AT

  9. CompletionProtocol Commit Rollback I C Committed Aborted

  10. 2PC Protocol Prepare Rollback Commit C P Prepared ReadOnly Aborted Committed Replay

  11. Volatile versusDurable 2PC • Two variants of 2PC protocol • One for volatile resources (e.g., cache) • One for durable resources (e.g., database) • Phase 1 has sub-phases A) Prepare all volatile participants • This can cause more durable participant registrations B) Prepare all durable participants

  12. WS-Addressing • Specification uses WS-Addressing • Important for interoperability • Different message classifications • Request messages • Reply messages • Notification messages • Fault messages

  13. Commit message <soapenv:Header> <wsa:To>http://localhost:8080/ws-t/Durable2PCParticipant</wsa:To> <wsa:ReplyTo> <wsa:Address>http://localhost:8080/ws-t/Durable2PCCoordinator</wsa:Address> <wsa:ReferenceProperties> <wsarjaddr:InstanceIdentifier>7f000001:8018:4369ea05:e</wsarjaddr:InstanceIdentifier> </wsa:ReferenceProperties> </wsa:ReplyTo> <wsa:Action>http://schemas.xmlsoap.org/ws/2004/10/wsat/Commit</wsa:Action> <wsarjaddr:InstanceIdentifier>7f000001:8018:4369ea05:c</wsarjaddr:InstanceIdentifier> <wsa:MessageID>AUID:ef3bda4cf07c9add</wsa:MessageID> </soapenv:Header> <soapenv:Body> <wsat:Commit/> </soapenv:Body>

  14. Committedmessage <soapenv:Header> <wsa:To>http://localhost:8080/ws-t/Durable2PCCoordinator</wsa:To> <wsa:Action>http://schemas.xmlsoap.org/ws/2004/10/wsat/Committed</wsa:Action> <wsarjaddr:InstanceIdentifier>7f000001:8018:4369ea05:e</wsarjaddr:InstanceIdentifier> <wsa:MessageID>AUID:ca2178bb6e56949c</wsa:MessageID> </soapenv:Header> <soapenv:Body> <wsat:Committed/> </soapenv:Body>

  15. Policy assertions • Transaction flow assertion • <wsat:ATAssertion wsp:optional=“true”/> • Operation Policy Subject • Used by applications to indicate willingness to accept incoming transactions • Wire format of serialized transaction is <wscoor:CoordinationContext> header • Atomic service assertion • <wsat:ATAlwaysCapability /> • Operation Policy Subject • Used by applications to indicate that a requester’s message will be processed transactionally

  16. Resources • WS-AtomicTransaction • http://schemas.xmlsoap.org/ws/2004/10/wsat/default.htm • Web services whitepapers, specs, workshops • http://msdn.microsoft.com/webservices/ • http://www-128.ibm.com/developerworks/webservices/library/specification/ws-tx/ • http://www.arjuna.com/library/

  17. State tables (perparticipant)

  18. State tables

  19. Workshops • March 2004 for feedback workshop • January 2005 for interoperability workshop • http://msdn.microsoft.com/webservices/community/workshops/transactionsinterop1204.aspx • Several public endpoints, including … • http://wsi.alphaworks.ibm.com:8080/wstx/services/InteropService • http://mssoapinterop.org/ws/

  20. Testing scenarios • Explicitly tested WS-AT and WS-BA • Implicitly tested WS-C • Many different test cases • Both for coordinator and participants • Included failures

  21. General flow

  22. Interoperability results

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