Low-Latency Multi-Writer Atomic Registers

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Course: Decentralized Systems (12min): Low-Latency Multi-Writer Atomic Registers.
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Low-Latency Multi-Writer Atomic Registers

  1. 1. Towards Feasible Implementations of Low-Latency Multi-Writer Atomic RegistersChryssis Georgiou, Nicolas Nicolaou,Alexander C. Russell, Alexander A. ShvartsmanMaria Stylianou – marsty5@gmail.com34335 DS – Decentralized Systems
  2. 2. 2 Overview • Problem, Theory & Motivation • Contributions ▫ APRX-SFW algorithm ▫ CWFR algorithm • Experiments & Results • Conclusions34335 DS – Decentralized Systems
  3. 3. 3 ProblemDistributedStorage System• Data Replication• Servers Failures• Read/Write Operations• Consistency?34335 DS – Decentralized Systems
  4. 4. 4 Conditions for Consistency Safety Regularity Atomicity34335 DS – Decentralized Systems
  5. 5. 5 Model Characteristics • MWMR • Asynchrony • Concurrency • Fault Tolerance • Availability 3 Sets of Processes • R: readers • Reliability • W: writers • 1 operation / 1 process • S: servers34335 DS – Decentralized Systems
  6. 6. 6 Model CharacteristicsQuorum Systems Efficiency Read/Write ops Latency Communication cost Communication cost FAST:1 comm-round + SLOW: 2 comm-round Computation cost34335 DS – Decentralized Systems
  7. 7. 7 Model Characteristics Communication Round 1. User sends msg to a set of servers 2. Each server that receives msg  replies with ACK 3. User receives ACK from a quorum of serversTag <timestamp, wid>• timestamp: counter• wid: last writer’s id34335 DS – Decentralized Systems
  8. 8. 8 Motivation & Contributions • Motivation – SFW algorithm ▫ Use of predicates ▫ Pros: Fast READ/WRITE ops ▫ Cons#1: Too much computation ▫ Cons#2: Dependent on the QS construction • Contribution – APRX-SFW algorithm ▫ Polynomial log-approximation complexity ▫ Speeds up computation of SFW34335 DS – Decentralized Systems
  9. 9. 9 Contributions: CWFR Algorithm • Independent from the QS construction! • Writer – 2 rounds ▫ 1st round: Send a READ to find the most recent tag ▫ 2nd round: Increase tag & Send a WRITE msg • Reader – 1 or 2 round(s) ▫ 1st round: Send a READ to find the most recent tag ▫ Use of Quorum Views  Decide if 2nd round is needed • Server – passive role ▫ Answers to received messages34335 DS – Decentralized Systems
  10. 10. 10 Quorum Views Qj • 1st check: All servers of Qj keep the latest tag  qView(1) (a) ▫ WRITE is complete READ FAST!34335 DS – Decentralized Systems
  11. 11. 11 Quorum Views Qj • 1st check: All servers of Qj keep the latest tag  qView(1) (a) ▫ WRITE is complete READ FAST! • 2nd check: There is at least one intersection where all servers keep the latest tag  qView(3) (c + d) ▫ No info if WRITE is complete  READ SLOW!34335 DS – Decentralized Systems
  12. 12. 12 Quorum Views Qj • 1st check: All servers of Qj keep the latest tag  qView(1) (a) ▫ WRITE is complete READ FAST! • 2nd check: There is at least one intersection where all servers keep the latest tag  qView(3) (c + d) ▫ No info if WRITE is completed  READ SLOW! • 3rd check: Each intersection has an older tag  qView(2) (b) ▫ Remove servers with latest tag and repeat checks34335 DS – Decentralized Systems
  13. 13. 13 QS with small intersection degree SIMPLE APRX-SFW CWFR34335 DS – Decentralized Systems
  14. 14. 14 QS with large intersection degree SIMPLE CWFR APRX-SFW34335 DS – Decentralized Systems
  15. 15. 15 Conclusions • Performance of APRX-SFW ▫ Number of writers ▫ Intersection degree • CWFR has more stable performance34335 DS – Decentralized Systems
  16. 16. 16 Web References • Towards Feasible Implementations of Low- Latency Multi-Writer Atomic Registers, http://www.cs.ucy.ac.cy/fastMWMR/pubs/MW MR_NCA11_IEEE.pdf • Towards Feasible Implementations of Low- Latency Multi-Writer Atomic Registers, Technical Report, http://www.cs.ucy.ac.cy/fastMWMR/MWMR- TR.pdf34335 DS – Decentralized Systems
  17. 17. Towards Feasible Implementations of Low-Latency Multi-Writer Atomic RegistersChryssis Georgiou, Nicolas Nicolaou,Alexander C. Russell, Alexander A. ShvartsmanMaria Stylianou – marsty5@gmail.com34335 DS – Decentralized Systems

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