Low-Latency Multi-Writer Atomic Registers

Towards Feasible Implementations

of Low-Latency Multi-Writer Atomic

Registers

Chryssis Georgiou, Nicolas Nicolaou,

Alexander C. Russell, Alexander A. Shvartsman

Maria Stylianou – [email protected]

34335 DS – Decentralized Systems

mailto:[email protected]

Overview

• Problem, Theory & Motivation

• Contributions

▫ APRX-SFW algorithm

▫ CWFR algorithm

• Experiments & Results

• Conclusions


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Problem


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Distributed Storage System

• Data Replication

• Servers Failures

• Read/Write Operations

• Consistency?

Conditions for Consistency


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Safety

Regularity

Atomicity

Model Characteristics

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• MWMR

• Asynchrony

• Concurrency

• Fault Tolerance

• Availability

• Reliability

• 1 operation / 1 process

3 Sets of Processes • R: readers • W: writers • S: servers




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Quorum Systems

Efficiency

Read/Write ops Latency

Communication cost FAST:1 comm-round

SLOW: 2 comm-round

Communication cost +

Computation cost



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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 servers

Tag <timestamp, wid>

• timestamp: counter • wid: last writer’s id

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 SFW

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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 messages


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Quorum Views

• 1st check: All servers of Qj keep the latest tag qView(1) (a)

▫ WRITE is complete READ FAST!


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Qj

Quorum Views



• 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!


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Qj

Quorum Views



• 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 checks


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Qj

QS with small intersection degree


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APRX-SFW

CWFR

SIMPLE

QS with large intersection degree


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SIMPLE

APRX-SFW

CWFR

Conclusions

• Performance of APRX-SFW

▫ Number of writers

▫ Intersection degree

• CWFR has more stable performance


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Web References

• Towards Feasible Implementations of Low-Latency Multi-Writer Atomic Registers, http://www.cs.ucy.ac.cy/fastMWMR/pubs/MWMR_NCA11_IEEE.pdf

• Towards Feasible Implementations of Low-

Latency Multi-Writer Atomic Registers, Technical Report, http://www.cs.ucy.ac.cy/fastMWMR/MWMR-TR.pdf


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http://www.cs.ucy.ac.cy/fastMWMR/pubs/MWMR_NCA11_IEEE.pdf



http://www.cs.ucy.ac.cy/fastMWMR/MWMR-TR.pdf



Towards Feasible Implementations

of Low-Latency Multi-Writer Atomic

Registers

Chryssis Georgiou, Nicolas Nicolaou,

Alexander C. Russell, Alexander A. Shvartsman

Maria Stylianou – [email protected]


mailto:[email protected]

Low-Latency Multi-Writer Atomic Registers

Education

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