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Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
Cap Theorem
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Cap Theorem

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  • 1. CAP Theorem The art of choice @mlomnicki
  • 2. CAP Theorem by Eric Brewer in 2000Proven in 2002 by Seth Gilbert & Nancy Linch
  • 3. CAP Theorem Consistency Availability Partition toleranceAt most 2 of 3 properties may be satisfied
  • 4. CAP Theorem
  • 5. RDBMS (single-site and cluster) Consistency Availability Partition tolerance
  • 6. Distributed RDBMS Consistency Availability Partition tolerance
  • 7. NoSQL Consistency AvailabilityPartition tolerance ...also DNS is AP
  • 8. BigTable Consistency AvailabilityPartition tolerance P is on GFS side
  • 9. Prevayler/Madeleine Consistency Availability Partition tolerance
  • 10. NewSQL Consistency AvailabilityPartition toleranceImpossible according to the theory ...but Stonebraker doesnt agree
  • 11. Real life stories
  • 12. What you think you have
  • 13. What you really have
  • 14. ..to be fair
  • 15. The art of choiceScalability over ConsistencyConsistency over Scalability
  • 16. Forfeit Partition ToleranceConsistent system - easyHigh Availability - hardknown & proven HA workaroundsFacebook - MySQL + memcacheVertical scalability
  • 17. Forfeit ConsistencyHigh AvailabilityHorizontal scalability - better"Eventually consistent" (BASE)HA = race conditionsworkarounds?
  • 18. What you needExtremely efficientReliable (in data sense)
  • 19. ACIDAtomicityConsistencyIsolationDurability
  • 20. BASEBasically AvailableSoft stateEventual consistency
  • 21. ACIDpeople dont care...but think data is consistent anywayyou cant enforce consistency atActiveRecord level
  • 22. BASEconsistency relaxedto make horizontal scalability easierinconsistencies handled by developer
  • 23. beware of vendorsthey dont always tell the truthNoSQL is never ACID-compilantNoSQL - lack of atomic operationsacross documents/collectionsPrevayler - poor isolationHBase - poor durability
  • 24. SQL is ACIDexcept MySQL with MyISAMMVCC over lockingbut must follow the rulesforeign keys, unique indexestransaction isolation levels
  • 25. LinksCAP presoCAP proofCAP explainedCAP and NoSQLComparisionStonbraker on CAPSharding limitsmore on CAP
  • 26. Questions?

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