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Distributed system notes, Assignments of Distributed Database Management Systems

Tribhuvan University KathmanduDistributed Database Management Systems

notes of a unit from distributed system

Typology: Assignments

2019/2020

Uploaded on 07/26/2025

rima-shrestha
rima-shrestha 🇳🇵

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Unit-7 Consistency and
Replication
7.1 Introduction
7.2 Data-centric consistency models
7.3 Client-centric consistency models
7.4 Replica management
7.5 Consistency protocols
7.6 Cashing and replication in Web
Replication for improving performance
//Replication = sub replication
Replication for High-availability
Replication for Enhancing Scalability
Replication for securing Against Malicious Attacks
-If the minority of the servers that hold the data are malicious the non-
malicious servers can outvote the malicious servers, thus provide
security.
Number of servers with correct data outvote the faulty servers.
Why consistency?
-In DS with replicated data, one of the main problems is keeping data
consistent.
What is consistency and replication explain in detail?
Consistency Methods
-Data Centric Consistency Method
-Client Centric Consistency Method
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Unit-7 Consistency and

Replication

7.1 Introduction

7.2 Data-centric consistency models

7.3 Client-centric consistency models

7.4 Replica management

7.5 Consistency protocols

7.6 Cashing and replication in Web

Replication for improving performance

//Replication = sub replication

Replication for High-availability

Replication for Enhancing Scalability

Replication for securing Against Malicious Attacks

- If the minority of the servers that hold the data are malicious the non- malicious servers can outvote the malicious servers, thus provide security. Number of servers with correct data outvote the faulty servers.

Why consistency?

- In DS with replicated data, one of the main problems is keeping data consistent.

What is consistency and replication explain in detail?

Consistency Methods -Data Centric Consistency Method -Client Centric Consistency Method

Introduction to Consistency and Replication

In a distributed system, shared data is typically stored in distributed shared memory, distributed databases or distributed file system.

- The storage can be divided across multiple computers. - Simply, we refer to a series of such data storage units as data-stores. Multiple processes can access shared data by accessing any replica on the data-store. - Processes generally perform read and write operations on the replicas. Types of consistency model Consistency models can be divided into two types: Data-Centric Consistency Models - These models define how the data updates are propagated across the replicas to keep them consistent. Client-Centric Consistency Model

  • These models assume that clients connect to different replicas at each time.
  • The models ensure that whenever a client connects to a replica the replica is bought up to date with the replica that the client accessed previously.

Data-centric Consistency Models

Data-centric Consistency Models describe how the replicated data is kept consistent and what the process can expect. Consistency Specification Models: Models for consistent

Consistency Specification Models

There are two types of permanent replicas:- -Primary servers -One or more servers in an organization -Whenever a request arrives, it is forwarded into one of the primary servers -Mirror sites -Geographically spread and replicas are generally statically configured -Server Initiated Replicas Third parties owner/providers -Client initiated replicas -Client initiated replicas are known as client cache -Client cache are used only to reduce the access latency of data For example browser casing locally Consistency protocol A consistency protocol describes the implementation of a specific consistency model there are three consistency model we are going to study they are:- -Primary based protocol One primary coordinator is elected to control replication across multiple replicas -Replicated write protocols Multiple replicas coordinate to provide consistency guarantee -Cache coherence protocol A special cache of client controlled replications.

Important question

Fully explain consistency model and briefly explain what is replication?