CAP Theorem

Transcript

1. CAP Theorem The art of choice @mlomnicki
2. CAP Theorem by Eric Brewer in 2000 Proven in 2002 by Seth Gilbert & Nancy Linch
3. CAP Theorem Consistency Availability Partition tolerance At 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 Availability Partition tolerance ...also DNS is AP
8. BigTable Consistency Availability Partition tolerance P is on GFS side
9. Prevayler/Madeleine Consistency Availability Partition tolerance
10. NewSQL Consistency Availability Partition tolerance Impossible according to the theory ...but Stonebraker doesn't agree
11. Real life stories
12. What you think you have
13. What you really have
14. ..to be fair
15. The art of choice Scalability over Consistency Consistency over Scalability
16. Forfeit Partition Tolerance Consistent system - easy High Availability - hard known & proven HA workarounds Facebook - MySQL + memcache Vertical scalability
17. Forfeit Consistency High Availability Horizontal scalability - better "Eventually consistent" (BASE) HA = race conditions workarounds?
18. What you need Extremely efficient Reliable (in data sense)
19. ACID Atomicity Consistency Isolation Durability
20. BASE Basically Available Soft state Eventual consistency
21. ACID people don't care ...but think data is consistent anyway you can't enforce consistency at ActiveRecord level
22. BASE consistency relaxed to make horizontal scalability easier inconsistencies handled by developer
23. beware of vendors they don't always tell the truth NoSQL is never ACID-compilant NoSQL - lack of atomic operations across documents/collections Prevayler - poor isolation HBase - poor durability
24. SQL is ACID except MySQL with MyISAM MVCC over locking but must follow the rules foreign keys, unique indexes transaction isolation levels
25. Links CAP preso CAP proof CAP explained CAP and NoSQL Comparision Stonbraker on CAP Sharding limits more on CAP
26. Questions?