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Consistency Tradeoffs in Modern Distributed Database System Design


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Slide for SDS homework. Original article can be downloaded from

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Consistency Tradeoffs in Modern Distributed Database System Design

  1. 1. Consistency Tradeoffs in ModernDistributed Database System DesignArticle by Daniel J. Abadi, YaleUniversityPresentation by Arinto Murdopo
  2. 2. Outline• CAP Theorem• What’s wrong with CAP?• Consistency/Latency Tradeoff• Type of Replication• PACELC• DDBS in PACELC metrics• Conclusion
  3. 3. CAP theorem Consistency Availability CA CP AP Partition Tolerance
  4. 4. What’s wrong with CAP? Consistency CA Availability Reduced Consistency, CP AP let’s justify it! Partition Tolerance(?)Tolerant to network partitionHigh availability Sacrifice consistency
  5. 5. What’s wrong with CAP?The P in CAP is combination of:• Partition tolerance ~ commonly used as justification• Existence of a network partition itself ~ often forgotten
  6. 6. Consistency/Latency TradeoffModern Database Design• Dynamo ~ Amazon• Cassandra ~ Facebook Availability & Latency• Voldemort ~ LinkedIn are critical!• PNUTS ~ YahooHigh Availability -> Replication is neededReplication is used -> Consistency/Latency Tradeoffoccurs
  7. 7. Type of Replication1. Data updates sent to all replicas at same time a. Without preprocessing layer ~ latency b. With preprocessing layer ~ consistency2. Data updates sent to agreed-upon location first a. Synchronous ~ consistency b. Asynchronous ~ latency. Used by PNUTS. c. Combination ~ configurable
  8. 8. Type of Replication3. Data updates sent to an arbitrary location• Location for data item is not always same a. Synchronous ~ consistency b. Asynchronous ~ latency• Used by Dynamo, Cassandra, and Riak -> combined with 2c
  9. 9. PACELCP ~ when there is partitioning• Trade off between ACE ~ else (which is no partitioning)• Trade off between LC
  10. 10. DDBS in PACELC metricsDBSS A C L CDynamo v vCassandra v vRiak v vVoltDB/H-Store v vMegastore v vMongoDB v vPNUTS v vDynamo, Cassandra and Riak have user-adjustable settings in LC tradeoff!
  11. 11. Conclusion• CAP is still important• Exploring new metrics is good• PACELC metrics are worth to consider