Distributed Databases Overview

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Questions and Answers

What is a characteristic of a fully replicated distributed database?

  • The entire database is replicated at every site. (correct)
  • Each fragment is stored at multiple sites.
  • Data is allocated nonredundantly.
  • Only some data fragments are replicated.

Which type of distributed database management system (DDBMS) operates with uniform software across all nodes?

  • Client-server architecture
  • Heterogeneous DDBMS
  • Multi-database system
  • Homogeneous DDBMS (correct)

What type of data allocation involves storing each fragment at only one site?

  • Partial replication
  • Homogeneous distribution
  • Fully replicated allocation
  • Nonredundant allocation (correct)

Which of the following issues may arise in federated database management systems?

<p>Semantic heterogeneity (D)</p>
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In a client-server database architecture, what do clients run?

<p>Client software to access databases (B)</p>
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What is one of the primary components of a distributed computing system?

<p>Interconnected nodes (D)</p>
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Which type of transparency allows users to access data without needing to know its physical location?

<p>Location transparency (D)</p>
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What defines the reliability of a distributed system?

<p>The probability it is functioning at a specific time (D)</p>
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Which characteristic describes the system’s ability to continue functioning during network partitioning?

<p>Partition tolerance (B)</p>
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What aspect of a distributed database ensures that certain types of faults do not affect the overall system's availability?

<p>Fault isolation (C)</p>
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Which type of autonomy refers to the independence of data models and transaction management techniques?

<p>Design autonomy (D)</p>
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Which of the following is NOT an advantage of distributed databases?

<p>Lowered initial setup costs (A)</p>
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What type of scalability involves expanding the number of nodes in a distributed database?

<p>Horizontal scalability (A)</p>
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What is horizontal fragmentation also known as?

<p>Sharding (C)</p>
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What operation is used to reconstruct a relation from complete vertical fragmentation?

<p>OUTER JOIN (A)</p>
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Which type of fragmentation keeps only certain attributes of a relation?

<p>Vertical fragmentation (D)</p>
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What is the primary purpose of replication in distributed systems?

<p>To enhance performance and availability (B)</p>
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How are mixed fragmentations defined?

<p>A combination of horizontal and vertical fragmentations (A)</p>
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What does complete horizontal fragmentation require to reconstruct the original relation?

<p>UNION operation (B)</p>
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Which of the following describes a drawback of non-distributed systems compared to distributed systems?

<p>Higher scalability challenges (B)</p>
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What does replication strategy involve in distributed systems?

<p>Storing fragments and replicas across nodes (C)</p>
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Flashcards

Distributed Computing System

A system that uses interconnected nodes to perform tasks efficiently, allowing for collaboration and distributed processing.

Distributed Database

A collection of interconnected databases spread across a computer network.

Distributed Database Management System (DDBMS)

A software system responsible for managing and coordinating operations in a distributed database, ensuring data consistency and integrity.

Transparency in Distributed Databases

The ability of a distributed database system to hide its internal implementation details from users, providing a seamless and transparent experience.

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Availability in Distributed Databases

The probability that a distributed system is continuously available for a specified period.

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Reliability in Distributed Databases

The probability that a distributed system is operational (not down) at a specific point in time.

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Scalability in Distributed Databases

The ability of a distributed database system to expand its capacity to accommodate increased workload.

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Partition Tolerance in Distributed Databases

The ability of a distributed database system to continue operating even when parts of the network are disconnected.

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Fully replicated distributed database

Every site in the system stores the entire database.

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Nonredundant data allocation

Each fragment of data is stored at only one site.

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Partial Replication

Some data fragments are replicated, while others are not.

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Homogeneous DDBMS

All nodes in the system use identical software configurations.

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Heterogeneous DDBMS

Different nodes in the system have different hardware and software configurations.

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Data Fragmentation

Breaking down a database table into smaller chunks called fragments, which are then distributed across different nodes in a distributed system.

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Horizontal Fragmentation (Sharding)

A method of data fragmentation that divides a table horizontally, according to conditions or other methods, creating groups of rows called shards.

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Vertical Fragmentation

A method of data fragmentation that divides a table vertically, according to columns, keeping only specific attributes in each fragment.

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Complete Horizontal Fragmentation

A method to reconstruct a relation (table) from fragmented parts, using a UNION operation to combine all the fragments.

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Complete Vertical Fragmentation

A method to reconstruct a relation (table) from fragmented parts, using an OUTER JOIN operation to combine all the fragments.

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Mixed Fragmentation

Combining both horizontal and vertical fragmentation, creating a more complex yet flexible distribution of data.

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Replication and Allocation

Strategies for storing fragments and their replicas across nodes in a distributed system, ensuring performance and data availability.

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Study Notes

Distributed Databases

  • Distributed computing systems consist of interconnected nodes
  • These nodes work together to perform tasks efficiently
  • Distributed databases connect database nodes over a computer network
  • The connected databases form a logical interrelation
  • Databases might not have homogeneity among the nodes
  • A distributed database management system (DDBMS) handles the distributed database

Introduction

  • A distributed database is a collection of multiple databases spread across different physical locations
  • Accessing data in a centralized database takes more time than in a distributed database for multiple users
  • Modification, management, and backup are more challenging in distributed databases compared to centralized ones
  • A uniform view is harder to provide to users across locations
  • Data consistency may be affected in distributed databases
  • User access may be reduced if one database fails, but distributed databases have access to multiple others
  • Distributed databases are more costly compared to centralized ones

Transparency

  • Transparency hides implementation details from users, giving a seamless experience
  • Types of transparency include data organization, location, naming, replication, fragmentation (horizontal and vertical), design, and execution transparency

Availability and Reliability

  • Availability is the probability of a system being continuously operational during a time interval
  • Reliability shows the probability that a system operates without issues at any given time

Scalability and Partition Tolerance

  • Horizontal scalability increases the number of nodes
  • Vertical scalability improves the capacity of individual nodes
  • Partition tolerance ensures system operation even during network partition

Autonomy

  • Autonomy describes the extent where nodes can operate independently
  • Types of autonomy include design (data model and transaction), communication (sharing information), and execution (user actions)

Advantages of Distributed Databases

  • Application development can occur in different geographic locations
  • Failures in one location don't affect overall availability
  • Data localization reduces network traffic, improving performance
  • Expansion is easier, whether by adding new nodes or improving individual node capacity

Data Fragmentation, Replication, and Allocation Techniques

  • Fragments are logical units of a database distributed across nodes
  • Horizontal fragmentation divides a relation into parts based on conditions or methods
  • Vertical fragmentation segments a relation by columns, keeping necessary attributes
  • Replication and allocation strategies manage fragment and replica storage across nodes for performance and availability
  • Fully replicated databases copy the entire database on all sites
  • Non-redundant allocation stores each fragment in a specific location
  • Partial replication duplicates some but not all fragments

Mixed Fragmentation

  • Combining horizontal and vertical fragmentation techniques

Types of Distributed Database Systems

  • Homogeneous DDBMS: Uses the same software on all nodes
  • Heterogeneous DDBMS: Uses different software and configurations on different nodes
  • Federated databases (FDBS): Feature a shared global schema, with issues involving differences in data models, constraints, query languages, and semantic heterogeneity

Client-Server Database Architecture

  • Client-server architecture includes client software, servers providing database functions, and a reliable communication infrastructure

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