Minimizing Coordination in Replicated Systems
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The document discusses minimizing coordination in replicated systems to enhance performance and consistency. It introduces the concept of partial order-restriction (por) consistency, emphasizing the role of visibility restrictions and the relationship between operations in ensuring system correctness. Key takeaways include the identification of minimal coordination plans and the necessity of certain restrictions to maintain system invariants and state convergence.
![MPI-SWS/NOVALINCS
Fast Internet services
Build replicated systems that are fast and correct
4/13/2015 Cheng Li @ PaPoC'15 2
[Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]](https://image.slidesharecdn.com/porconsistencypapoc2015-150425144210-conversion-gate02/85/Minimizing-Coordination-in-Replicated-Systems-2-320.jpg)
![MPI-SWS/NOVALINCS
Fast Internet services
Build replicated systems that are fast and correct
4/13/2015 Cheng Li @ PaPoC'15
Blue ops: no coordination, weak consistency
3
[Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]](https://image.slidesharecdn.com/porconsistencypapoc2015-150425144210-conversion-gate02/85/Minimizing-Coordination-in-Replicated-Systems-3-320.jpg)
![MPI-SWS/NOVALINCS
Fast Internet services
Build replicated systems that are fast and correct
4/13/2015 Cheng Li @ PaPoC'15
State
convergence
Invariant
preservation
Blue ops: no coordination, weak consistency
4
[Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]](https://image.slidesharecdn.com/porconsistencypapoc2015-150425144210-conversion-gate02/85/Minimizing-Coordination-in-Replicated-Systems-4-320.jpg)
![MPI-SWS/NOVALINCS
Fast Internet services
Build replicated systems that are fast and correct
4/13/2015 Cheng Li @ PaPoC'15
Blue ops: no coordination, weak consistency
Red ops: coordination, stronger consistency
5
State
convergence
Invariant
preservation
[Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]](https://image.slidesharecdn.com/porconsistencypapoc2015-150425144210-conversion-gate02/85/Minimizing-Coordination-in-Replicated-Systems-5-320.jpg)
Minimizing Coordination in Replicated Systems
- 1. Minimizing Coordination in Replicated systems Cheng Li Max Planck Institute for Software Systems Joint work with João Leitão, Allen Clement, Nuno Preguiça, and Rodrigo Rodrigues
- 2. MPI-SWS/NOVALINCS Fast Internet services Build replicated systems that are fast and correct 4/13/2015 Cheng Li @ PaPoC'15 2 [Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]
- 3. MPI-SWS/NOVALINCS Fast Internet services Build replicated systems that are fast and correct 4/13/2015 Cheng Li @ PaPoC'15 Blue ops: no coordination, weak consistency 3 [Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]
- 4. MPI-SWS/NOVALINCS Fast Internet services Build replicated systems that are fast and correct 4/13/2015 Cheng Li @ PaPoC'15 State convergence Invariant preservation Blue ops: no coordination, weak consistency 4 [Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]
- 5. MPI-SWS/NOVALINCS Fast Internet services Build replicated systems that are fast and correct 4/13/2015 Cheng Li @ PaPoC'15 Blue ops: no coordination, weak consistency Red ops: coordination, stronger consistency 5 State convergence Invariant preservation [Making Geo-Replicated Systems Fast as Possible, Consistent when necessary, OSDI’12]
- 6. MPI-SWS/NOVALINCS How to coordinate red ops? • Totally order all of them – simple but sometimes too conservative/costly • Observation: a red op only needs to be ordered w.r.t other relevant red ops. • E.g., auction service – Bid + close auction operations – Invariant: highest accepted bid is declared winner 4/13/2015 Cheng Li @ PaPoC'15 6
- 7. MPI-SWS/NOVALINCS bidder price Replicated auction service 7Cheng Li @ PaPoC'154/13/2015 UKUS bid($10) winner bidder price Bob 10 winner bidder price
- 8. MPI-SWS/NOVALINCS bidder price Replicated auction service 8Cheng Li @ PaPoC'154/13/2015 UKUS winner bidder price Bob 10 winner bidder price bid($15) bidder price Alice 15
- 9. MPI-SWS/NOVALINCS bidder price Replicated auction service 9Cheng Li @ PaPoC'154/13/2015 UKUS winner bidder price Bob 10 winner bidder pricebidder price Alice 15 close() winner Bob
- 10. MPI-SWS/NOVALINCS Replicated auction service 10Cheng Li @ PaPoC'154/13/2015 UKUS Bob won even with a lower bid than Alice. bidder price Bob 10 winner bidder price Alice 15 winner Bob bidder price Alice 15 Bob 10 bidder price Alice 15 Bob 10 winner Bob
- 11. MPI-SWS/NOVALINCS Less coordination is better! 4/13/2015 Cheng Li @ PaPoC'15 11 bid bid close bid bid bid close bid bid
- 12. MPI-SWS/NOVALINCS Less coordination is better! 4/13/2015 Cheng Li @ PaPoC'15 12 bid bid close bid bid bid close bid bid Visibility restriction A partial order enforcing visibility restrictions Pros: fine-grained tuning in consistency semantics (the amount of coordination) using restrictions
- 13. MPI-SWS/NOVALINCS Outline • Background • Partial order-Restriction (PoR) consistency – Visibility restrictions – Consistency model • Restriction inference • Conclusion 4/13/2015 Cheng Li @ PaPoC'15 13
- 14. MPI-SWS/NOVALINCS Outline • Background • Partial order-Restriction (PoR) consistency – Visibility restrictions – Consistency model • Restriction inference • Conclusion 4/13/2015 Cheng Li @ PaPoC'15 14
- 15. MPI-SWS/NOVALINCS Visibility restrictions • A restriction between two operations implies that one must see effects introduced by the other. • For operation 𝑎, 𝑏, the restriction 𝑟 𝑎, 𝑏 implies that 𝑎 ≺ 𝑏 𝑏 ≺ 𝑎 w.r.t any partial order ≺. 4/13/2015 Cheng Li @ PaPoC'15 15 a0 b0 a1 a2 b1 b2 If 𝑎 ≺ 𝑏 𝑏 ≺ 𝑎, then 𝑟 𝑎, 𝑏 is met in ≺.
- 16. MPI-SWS/NOVALINCS Partial order-restrictions (PoR) Consistency • A replicated system 𝑆 is associated with a set of restrictions 𝑅𝑠. – e.g., 𝑅𝑠 = {𝑟(𝑎, 𝑏), 𝑟(𝑐, 𝑑)} • 𝑆 is PoR Consistent if, for any its executions, there exists an admissible partial order, where all restrictions in 𝑅𝑠 are met. 4/13/2015 Cheng Li @ PaPoC'15 16
- 17. MPI-SWS/NOVALINCS Outline • Background • Partial order-Restriction (PoR) consistency – Visibility restrictions – Consistency model • Restriction inference • Conclusion 4/13/2015 Cheng Li @ PaPoC'15 17
- 18. MPI-SWS/NOVALINCS Challenges • Which restrictions are sufficient? – They must ensure relevant properties. • Does the set of restrictions comprise a minimal coordination plan? – i.e., we cannot remove any restriction from the set. 4/13/2015 Cheng Li @ PaPoC'15 18
- 19. MPI-SWS/NOVALINCS Outline • Background • Partial order-Restriction (PoR) consistency • Restriction inference – State convergence – Invariant preservation • Conclusion 4/13/2015 Cheng Li @ PaPoC'15 19
- 20. MPI-SWS/NOVALINCS State convergence • Definition: all replicas reach the same final state when the system becomes quiescent. • Insight: any pair of operations must be ordered if they don’t commute. 4/13/2015 Cheng Li @ PaPoC'15 20
- 21. MPI-SWS/NOVALINCS Invariant preservation • Insight: for any violation, add restrictions among concurrent operations 4/13/2015 Cheng Li @ PaPoC'15 21 bid(“Bob”, 10) bid(“Alice”, 15) close() winner bidder price winner Bob bidder price Alice 15 Bob 10
- 22. MPI-SWS/NOVALINCS Invariant preservation (cont.) • Insight: for any violation, add restrictions among concurrent operations 4/13/2015 Cheng Li @ PaPoC'15 22 bid(“Bob”, 10) bid(“Alice”, 15) close() winner bidder price winner Bob bidder price Alice 15 Bob 10 Q: Can we remove any concurrent op while maintaining the violation?
- 23. MPI-SWS/NOVALINCS Invariant preservation (cont.) • Insight: for any violation, add restrictions among concurrent operations 4/13/2015 Cheng Li @ PaPoC'15 23 bid(“Bob”, 10) bid(“Alice”, 15) winner bidder price winner bidder price Alice 15 Bob 10 Q: Can we remove any concurrent op while maintaining the violation? A: close must be there.
- 24. MPI-SWS/NOVALINCS Invariant preservation (cont.) • Insight: for any violation, add restrictions among concurrent operations 4/13/2015 Cheng Li @ PaPoC'15 24 bid(“Bob”, 10) bid(“Alice”, 15) close() winner bidder price winner Bob bidder price Alice 15 Bob 10 Q: Can we remove any concurrent op while maintaining the violation?
- 25. MPI-SWS/NOVALINCS Invariant preservation (cont.) • Insight: for any violation, add restrictions among concurrent operations 4/13/2015 Cheng Li @ PaPoC'15 25 bid(“Alice”, 15) close() winner bidder price Bob 10 winner Bob bidder price Alice 15 Bob 10 Q: Can we remove any concurrent op while maintaining the violation? A: Yes, bid(“Bob”, 10).
- 26. MPI-SWS/NOVALINCS Invariant preservation (cont.) • Insight: for any violation, add restrictions among concurrent operations 4/13/2015 Cheng Li @ PaPoC'15 26 bid(“Alice”, 15) close() winner bidder price Bob 10 winner Bob bidder price Alice 15 Bob 10 This is a minimal violating execution. Solution: 𝑟(𝑏𝑖𝑑, 𝑐𝑙𝑜𝑠𝑒) Analysis: Step 1: For any such an execution, we add a restriction over a pair of its maximal operations. Step 2: Iterate all these executions
- 27. MPI-SWS/NOVALINCS Take-home points • Consistency semantics can be captured by visibility restrictions over operations. • Invariant and commutativity analysis finds the minimal set of restrictions to preserve convergence and invariants. • PoR Consistency enforces all restrictions throughout all executions of a replicated system. 4/13/2015 Cheng Li @ PaPoC'15 27
- 28. Minimizing Coordination in Replicated systems Thanks for your attention!