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An Approach to Reduce the Energy Cost of the Arbitrary Tree

Replication Protocol

e-Energy 2010

14. April, Passau, Germany

Robert Basmadjian and Hermann de Meer

Overview Replication

Replication is used to:

Achieve fault-tolerance

Improve the system performance

Multiple replicas lead to inconsistency problems

Replica Control Protocols (RCPs) ensure synchronization

RCPs implement two operations: read and write

To ensure one-copy equivalence:

Write operation stores a new value of data

Read operation returns the most recent value written

2An Approach to Reduce the Energy Cost of the Arbitrary Tree Replication Protocole-Energy 2010, 14. April, Passau, Germany

Overview Replication

Quorum systems serve as a tool to achieve one-copy equivalence:

Pair-wise non-empty intersections of quorums

Quorum-based RCPs differ according to three parameters:

Quorum size

Availability

Load

Quorum-based RCPs can be classified into:

Non-structured

Structured


Overview Energy Efficiency

Building energy-efficient distributed systems:

Increase of energy costs (fuel)

Desire to reduce CO2 emissions

Minimizing and balancing the system’s energy consumption are as important as:

Reliability

Security

Fault tolerance

Several techniques to save energy consumption

Desirable to keep the same overall performance level


Overview Motivation and Results

A model to compute the energy cost of each operation of quorum-based RCPs

An approach applied to a particular tree-structured RCP:

Cease the utilization of a significant amount of replicas

Reorganize the remaining replicas into a new logical structure

Obtained results:

Diminished overall energy consumption

Reduced energy cost of the operations

Comparable performance as the original protocol


Outline

Energy Cost Model

The Arbitrary Tree Protocol

Energy Efficient Approach

Comparison

Conclusion and Perspectives


Energy Cost Model

Each operation is carried out in two phases:

Sending the request to all the members of a quorum

Receiving the response from all the members of the quorum

The energy consumed is modeled by summing

The operation initiator’s component and connector

The quorum members’ components, connectors and storage media


Energy Cost Model An Example of a Read Operation

8

Logic and

to/from

connector

Logic, to/from

component and

remote

communication

An Approach to Reduce the Energy Cost of the Arbitrary Tree Replication Protocole-Energy 2010, 14. April, Passau, Germany

Client Replica

Logic, to/from

component,

remote

communication

and buffering

Logic, to/from

connector and

to/from disk

Disk access and

to/from

component

Energy Cost Model General Quorum-based Costs

Read operation:

rqSize*[(Replica’s component and connector) + (Storage access

for read) + (marshal and unmarshal) + (Remote connection) +

(Message sent) + (Message received)] + (Client’s component) +

(to/from component)

Write operation:

wqSize*[(Replica’s component and connector) + (Storage access

for write) + (marshal and unmarshal) + (Remote connection) +

(Message sent) + (Message received)] + (Client’s component) +

(to/from component)


The Arbitrary Tree Protocol

Nodes of the tree can be:

Logical

Physical (replica)

A physical level has at least one physical node

A logical level has all of its nodes logical

A read operation: any single replica of every physical level

A write operation: all replicas of a single physical level


The Arbitrary Tree Protocol An Example for 81 replicas


A logical root node

sqrt(n) = 9

4 replicas

(n – 28)/sqrt(n) – 7

26.5

n > 64

The Arbitrary Tree Protocol The Proposed Algorithm: Advantages

Read operations have a quorum size of sqrt(n), are highly available and induce a load of 0.25

Write operations have a quorum size of sqrt(n), are highly available and induce a load of 1/sqrt(n)


Energy Efficient ApproachOverview

Objectives:

Keep the same protocol as the one proposed for Arbitrary Tree

Reduce the energy consumption of AT protocol

Keep a comparable performance wrt AT protocol

Achievements

Logical rearrangement of the replicas into a rectangle structure

Cease the utilization of a significant amount of replicas

Data consistency is preserved


Energy Efficient ApproachRectangle Structure

Organize logically thereplicas into a rectangleof height h > 1 andwidth w > 1

Transformation:

Set the width of the rectangle to be 4

Set the height of the rectangle to be sqrt(n)


Energy Efficient ApproachTransformation


Comparison

Studies for n = 75, 100, 150 and 200 replicas

Every replica is up 70% of the time

For each operation, comparison is performed in terms of:

Quorum size (between 1 and n)

Availability (between 0 and 1)

Load (between 0 and 1)

Energy cost in terms of a single client-replica cost


ComparisonRead Operation


ComparisonWrite Operation


ComparisonSaved Energy Consumption

Number of Replicas Arbitrary Tree Rectangle

n = 75 0 39

n = 100 0 60

n = 150 0 102

n = 200 0 144


Conclusion and Perspectives

Compute the energy cost of quorum-based RCP

Approach to reduce the energy consumption of the AT protocol

Ceasing the usage of replicas

Logical transformation into a rectangle structure

Perspectives:

Expectation of energy cost in terms of load?

Read-only operations, select replicas with small PUE or good geographical regions (Iceland or Africa)

Compute the energy cost of other quorum-based RCP


Questions

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