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The DCon framework

The DCon framework. Vilmos Bilicki, József Dániel Dombi University of Szeged. Agenda. Issues with distributed systems Motivation Consistency Paxos P2P Paxos O ur solution The reliability of a laboratory Results Q&A. Issues with distributed systems.

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The DCon framework

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  1. The DCon framework Vilmos Bilicki, József Dániel Dombi University of Szeged

  2. Agenda • Issues with distributed systems • Motivation • Consistency • Paxos • P2P Paxos • Our solution • The reliability of a laboratory • Results • Q&A

  3. Issues with distributed systems • Is it worthwhile talking about distributed systems? • 7x24: e-business, e-government, e-health, e-* • A distributed system can provide different level of transparency: scalability, reliability, … • High reliability? • Replication is a typical solution • The participating nodes should have the same knowledge • How to build a distributed system • Cheap powerful desktop machines (LanStore) • Dedicated highly available servers

  4. Motivation • LanStore • Group Intelligence Module • It turned out that maintaining the distributed consistency in an efficient manner can be very challanging • Currently there is no framework for solving this issues for .NET environment • The goal of the DCon framework to provide efficient, reliable data replication

  5. Consistency • Every member node should have the same knowledge • Problems: • Bugs • Hardware error • Network error • System modell: • Asynchronous communication • The messages may be duplicated delayed and lost • The failures are being • Fail-stop and restart failures • No bysantine failures

  6. Paxos • Quororum based solution • Properties • It guaranties the consistency in the case of being failures • In most cases progres is guarantied • Goal: • A set of nodes, every node can propose values • Paxos ensures that only one is choosen • Abstractions: • Leader (serialisation, progress) • Quorum (fault tolerance) • Durable store • Non durable store • Paxos consensus algorithm (for guaranteing the consistency) • Message complexity: • Best case O(n) • Worst case O(3n)

  7. Paxos consensus algorithm A B C

  8. P2P Paxos • It is based on Windows P2P API • Windows P2P API • The consistency is provided by serial numbers and timestamps • There is no central knowledge of the list of members • There is a single node (root) for network maintenance • Our solution • We use distributed aggregation for • Calculating the membership • Collecting the responses • We used the root node to act as leader

  9. P2P Paxos 2 4 8 8 3 1 8 8 8/8 8 2 1 8 3 8 8

  10. Our solution • Two level of services • Reliable memory • System maintenance • Paxos algorithm with optimisations • Efficient gentle leader election algorithm

  11. The reliability of a laboratory I.

  12. The reliability of a laboratory II.

  13. The reliability of a laboratory III.

  14. Results

  15. Results

  16. Results

  17. Summary • The DCon framework provides efficient and safe data replication • It is based on an optimised version of the well known Paxos algorithm • We implemented the Paxos in a P2P environment • The solution can be used even in very changeable environment

  18. Current state/Future plans • Currently the framework is only partially implemented (Native IP based) • It will be finished this summer • It will be availble on the site: • http://dcon.sf.com • Future plans: • Study and implement a Web Service based component beside of the native IP and P2P based communication components

  19. Thank You for Your attention! Q&A

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