✓ ☑️ 107 Redundancy and Replication (Basics)
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Questions and Answers

What defines the primary-replica relationship in database replication?

  • The primary server receives all updates that are then shared. (correct)
  • Data is replicated only upon request from a replica.
  • Replica servers perform updates independently.
  • All servers exchange updates at the same time.

Which statement best describes synchronous replication?

  • Updates to replica databases can occur afterwards.
  • Changes must be replicated before a write is complete. (correct)
  • No confirmation is required from the replicas for updates.
  • Changes are applied concurrently on all servers.

In a primary-replica database setup, what is required from each replica server upon receiving an update?

  • A log file must be created before any updates are made.
  • The primary server must verify the update.
  • Each replica must acknowledge receipt of the update. (correct)
  • Replicas should update independently without notification.

Why is replication important in database management systems?

<p>It ensures data availability in case the primary server fails. (B)</p> Signup and view all the answers

How do replica servers manage updates received from the primary server?

<p>Updates are immediately applied upon receipt and acknowledged. (D)</p> Signup and view all the answers

What is the primary purpose of redundancy in a system?

<p>To create backups and improve reliability (D)</p> Signup and view all the answers

What happens if there is only a single copy of a file stored on a server?

<p>Losing the server results in losing the file (D)</p> Signup and view all the answers

How does redundancy help in crisis situations?

<p>It provides backups if needed (D)</p> Signup and view all the answers

What is the primary purpose of database replication?

<p>Data availability and fault tolerance (D)</p> Signup and view all the answers

In a system with redundancy, what occurs if one instance of a service fails?

<p>The service continues without interruption (B)</p> Signup and view all the answers

Which of the following is NOT a benefit of redundancy?

<p>Improved data processing (A)</p> Signup and view all the answers

What is the main goal of database replication in distributed systems?

<p>To allow multiple copies of data to enhance scalability (C)</p> Signup and view all the answers

Which of the following best describes a consequence of not having redundancy?

<p>Increased risk of system failure and data loss (A)</p> Signup and view all the answers

What is a key characteristic of asynchronous replication?

<p>Changes are queued and replicated later. (B)</p> Signup and view all the answers

What can result from the delay in asynchronous replication?

<p>Temporary inconsistencies may occur. (C)</p> Signup and view all the answers

Which statement accurately describes the operational difference of asynchronous replication compared to synchronous replication?

<p>Asynchronous replication introduces a delay in data updating. (C)</p> Signup and view all the answers

In asynchronous replication, what happens to changes made to the primary database?

<p>They are queued for later replication to replicas. (B)</p> Signup and view all the answers

What is a potential drawback of using asynchronous replication?

<p>Delay in data consistency across databases. (A)</p> Signup and view all the answers

How does asynchronous replication handle changes during peak loads?

<p>Changes are queued and processed later. (A)</p> Signup and view all the answers

Which of the following describes the state of replica databases immediately after changes are made to the primary database in asynchronous replication?

<p>They show the old data until the next replication. (A)</p> Signup and view all the answers

What should be expected from the data on replica databases in an asynchronous replication setup?

<p>Data may lag behind the primary database changes. (B)</p> Signup and view all the answers

What happens to the write operation in synchronous replication?

<p>It is acknowledged after replicas confirm receipt and processing. (C)</p> Signup and view all the answers

What is a major advantage of synchronous replication?

<p>It reduces the risk of data loss or inconsistency. (B)</p> Signup and view all the answers

In synchronous replication, how does the primary database operate?

<p>It waits for confirmation from replicas before proceeding. (B)</p> Signup and view all the answers

What can be inferred about the state of data in synchronous replication?

<p>Data is consistently updated across all databases simultaneously. (C)</p> Signup and view all the answers

Which of the following is NOT a feature of synchronous replication?

<p>Independent operation of primary and replica databases. (C)</p> Signup and view all the answers

Which aspect does synchronous replication prioritize?

<p>Data integrity and consistency. (A)</p> Signup and view all the answers

What could be a disadvantage of synchronous replication?

<p>Potential delays in write operations if replicas are slow. (A)</p> Signup and view all the answers

What distinguishes semi-synchronous replication from fully synchronous replication?

<p>At least one replica must confirm receipt of changes for the operation to be complete. (D)</p> Signup and view all the answers

In semi-synchronous replication, how are the changes propagated to the replicas?

<p>Only one replica is updated immediately; others may follow later. (C)</p> Signup and view all the answers

What is a benefit of semi-synchronous replication compared to fully synchronous replication?

<p>It provides improved performance. (B)</p> Signup and view all the answers

When does the write operation on the primary database end in semi-synchronous replication?

<p>After at least one replica confirms receipt of changes. (B)</p> Signup and view all the answers

Which characteristic best describes the consistency level achieved by semi-synchronous replication?

<p>Weaker than fully synchronous but stronger than asynchronous. (A)</p> Signup and view all the answers

What does the term 'asynchronously' imply in the context of semi-synchronous replication?

<p>Some replicas may update their data at different times. (C)</p> Signup and view all the answers

Which of the following is true about the confirmation of changes in semi-synchronous replication?

<p>At least one replica must process the changes for confirmation. (D)</p> Signup and view all the answers

What is a potential drawback of semi-synchronous replication compared to the fully asynchronous method?

<p>It may introduce latency due to waiting for confirmations. (B)</p> Signup and view all the answers

What is a key benefit of asynchronous replication?

<p>Write operations can be completed quickly without waiting for confirmation. (C)</p> Signup and view all the answers

What happens when one or more replica databases are unavailable in an asynchronous replication setup?

<p>Write operations can still be completed on the primary database. (D)</p> Signup and view all the answers

What characteristic differentiates semi-synchronous replication from other types of replication?

<p>It combines elements of both synchronous and asynchronous replication. (C)</p> Signup and view all the answers

Which statement correctly describes the performance aspect of asynchronous replication?

<p>It generally enhances the performance of write operations. (D)</p> Signup and view all the answers

In which situation is asynchronous replication most beneficial?

<p>When write availability is critical even with some database replicas offline. (D)</p> Signup and view all the answers

What is the potential trade-off of using asynchronous replication?

<p>Data consistency might be compromised due to replication delays. (D)</p> Signup and view all the answers

What is one advantage of writing operations in asynchronous replication?

<p>They can complete without waiting for replica confirmations. (D)</p> Signup and view all the answers

What primary feature does semi-synchronous replication retain from synchronous replication?

<p>It ensures some level of acknowledgment from replicas. (B)</p> Signup and view all the answers

How does redundancy differ from database replication in system design?

<p>Redundancy focuses on duplicating critical components or functions, whereas replication involves copying and synchronizing data across databases. (B)</p> Signup and view all the answers

Flashcards

Primary Server

The original database that receives updates and sends them to replicas.

Replica Servers

Copies of the primary database that receive updates from the primary server.

Synchronous Replication

A type of database replication where all updates are applied to replicas before the write operation is considered successful.

Replication Process

A process where the primary server sends updates to the replica servers, and each replica acknowledges receipt of the update before the next update is sent.

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Replica Acknowledgement

A message sent from a replica server to the primary server acknowledging that it has received and applied the update.

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Redundancy

Creating duplicate copies of essential parts or functions in a system to improve its reliability and handle failures.

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Single Point of Failure

A situation where a single component's failure can cause the entire system to fail.

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Failover

The process of switching to a backup system or component when the primary system fails.

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Database Replication

Duplicating data and keeping it synchronized across multiple databases.

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Data Availability

Ensuring data is accessible even if there are system failures.

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Fault Tolerance

The ability of a system to withstand failures without losing data or functionality.

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Scalability

The ability of a system to handle increasing workloads and user demands.

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Redundancy for Performance

Using redundancy to improve the performance of a system.

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Strong Consistency

All changes made to the primary database are immediately reflected in the replica databases.

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Benefits of Synchronous Replication

Ensures the data is consistent across all databases, reducing risks like data loss and inconsistency.

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Primary Database

A database that serves as the main source of data and distributes changes to other databases.

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Replica Databases

Databases that receive and process changes from the primary database.

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Replication

The process of updating replica databases with changes made to the primary database.

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Immediate Replication

When changes made to the primary database are immediately replicated to the replica databases, ensuring consistency between the two.

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Redundancy in Replication

Ensures that any errors or failures in one database won't affect the others.

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Change queue

Changes made to the primary database are temporarily stored in a queue before being applied to the replica databases.

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Replication delay

The time difference between a write operation on the primary database and the application of that change to the replica database.

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Inconsistency

A temporary state where the primary and replica databases hold different data due to the replication delay.

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Trade-off between availability and consistency

Asynchronous replication provides a trade-off between high availability and consistency. While replicas may not be completely up-to-date, the primary database remains available even if replicas are lagging behind.

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Use cases for asynchronous Replication

Asynchronous replication is suitable for applications where a slight delay in data updates on replicas is acceptable, such as reporting systems or backups.

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Semi-synchronous replication

A replication strategy that combines features of synchronous and asynchronous replication. It ensures data consistency by requiring a minimum number of replicas to acknowledge write operations, but allows for faster writes than fully synchronous replication.

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Write operations

In database replication, write operations are actions that modify data, such as adding, deleting, or updating information.

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Database unavailability

A situation where a database or other system is unavailable or unable to function.

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Data consistency in replication

The consistency of data across all replicas in a replication system. Ensuring that all replicas have the same data is important for preventing inconsistencies.

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Data replication

In database replication, the process of ensuring that data changes are applied to all replicas in a timely and consistent manner.

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Write Operation Confirmation

When a write operation on the primary database is not considered complete until at least one replica database has confirmed receiving and processing the changes.

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Fully Synchronous Replication

A type of replication where the primary database confirms receipt of all changes on all replica databases before proceeding.

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Performance Improvement

A performance benefit of semi-synchronous replication compared to the stricter fully synchronous approach.

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Study Notes

Redundancy

  • Redundancy duplicates critical components or functions of a system to increase reliability and improve performance
  • It often involves creating backups or fail-safes
  • If a server containing a file fails, the file is lost with no backup or redundant copy
  • Redundant copies of a file solve data loss problems
  • Redundancy removes single points of system failure and provides backups during crises
  • Redundancy is useful if a service in production fails
  • In case of service failure, the system can failover to another instance

Database Replication

  • Database replication copies and synchronizes data from one database to one or more additional databases
  • Databases include multiple copies of the same data to ensure data availability, fault tolerance, and scalability
  • Replication involves a primary and copy relationship
  • The primary server receives updates first, then relays updates to other replica servers
  • Replica servers confirm successful updates before sending subsequent updates
  • This ensures data integrity across all databases

Replication Strategies

  • Synchronous Replication:
    • Changes to the primary database are immediately replicated to replicas
    • The primary waits for replica confirmation before marking the write operation complete
    • Strong consistency between primary and replicas
    • Low risk of data loss
  • Asynchronous Replication:
    • Changes to the primary database aren't immediately replicated to replicas
    • There is a delay between the write operation on the primary database and the update on the replica databases
    • Temporary inconsistencies may exist
    • Performance benefits as write operations complete quickly
  • Semi-synchronous Replication:
    • Combines synchronous and asynchronous replication
    • Changes are immediately replicated to at least one replica database
    • The write operation only completes after at least one replica confirms receipt and processing of changes.
    • Some strong consistency between primary and replica databases
    • Provides improved performance compared to fully synchronous replication

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Description

This quiz covers the concepts of redundancy and database replication. It explores how redundancy increases reliability and performance in systems and explains the mechanisms behind data replication across databases. Understanding these topics is essential for ensuring data availability and fault tolerance.

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