Data Replication in

Mobile Computing

By-Vasundhara Ghose

Roll No. - 1036710012

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Topics Covered:O Replication in mobile Env. V/S

Distributed Env.O Internal view of replicationO Forms of ReplicationO Data Replications StrategiesO Database Replications

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Replication Revised O Maintenance and creation of copies

of data at multiple computers.O Provides-

O Enhanced performanceO High availabilityO High fault tolerance.O Backup plan

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Internal View of Replication system

Replica Planner

LocalizationManager

ConsistencyManager

StrategyManager

Application interface

Contextanalyzer

System State

Monitor

Replica databases

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Replication in mobile Env. V/S Distributed Env.

Distributed Systems

Mobile environment

O Fixed Infrastructure

O Fixed machinesO Permanently

connected n/wO Sufficient

resources

O Limited memory spaceO Disk spaceO Battery powerO Processor capacityO Device flexibilityO Mobility of usersO Multiterminal accessesO Nature of wireless n/wO Security & other

aspects

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Forms of Replication

Types

Single-Updater

Sys.

Multiple-Updater

Sys.

1. Single Updater Sys.2. Multiple Updater sys.

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SINGLE-UPDATER SYSTEM

O Only one user has right-to-update(RTU)

O Only one data update sourceO Replication is performed only by

“Snapshots” (Read-only copies)O Don’t worry about data collisions or

sequence generator conflicts

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MULTIPLE-UPDATER SYSTEM

O Updating one site from more than source at a time.

O Main Issue: DATA COLLISIONO E.g.; OLTP – online transaction ProcessingO Example: IBM’s CICS is well-known OLTP

product.O No locking mechanism(in async systems)O At time replication time- conflict resolving

strategies must be applied.

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Strategies of Replication

Types

Sync Replicatio

ns

Async Replicatio

ns

Push & Pull

Replication

1. Sync Replications2. Async Replications

3. Push & Pull Replication

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SYNCHRONOUS REPLICATIONS

Database(Main

)

Updating

node

Replicated

Database

Data recorded, now respond

Values are saved to replica

Wait..Request

Updating successful

Values are saved to main DB

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Synchronous replications

O Replica updating is a part of original transaction

O Is any site replicas are unavailable, transaction can’t committed.

O Large number of Msgs are required.O ADVANTAGE: 100% guaranteed of

NO loSS of data.

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Synchronous replications

OLong waiting timeO Impractical approachOLocation dependency of

primary and secondary

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Asynchronous replications

Database(Main

)

Updating

node

Values are saved to main DB

Replicated

Database

Data recorded, now respond

Values are saved to replica

Request

Updating successful

No Wait..

upd

ate

r

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Asynchronous replications

O Advantages: increased speedO Disadvantages: high risk of data loss

O Applications: server & network storage

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Push & Pull method of Replication

O Publisher: source database/s containing the info you want to replicate.

O Distributer: database/s reponsible for queuing replicated data from publisher

O Subscriber: destination database/s for data coming from Publisher.

(Terminology)

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Push & Pull method of Replication

O Push method: the distributor is responsible for queuing data from publisher>>then propagating to subscriber.

O Pull Method: the distributor is responsible for queuing data from publisher>>O Then subscriber is responsible for

grab all data ready for Replication.

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Database Replication

O Creation & maintenance of multiple copies of same database.

O Master-slave conceptO Helpful in load sharing(database

read)O Improve Availability

Types of database replications

Snapshot Replication

Merging Replication

s

Transactional

replications

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