Replication strategies in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is replication in database systems?

Replication is the process of copying and maintaining database objects, like data, across multiple servers to improve availability and reliability.

beginner

What is the main goal of replication strategies?

The main goal is to ensure data consistency, availability, and fault tolerance by managing how data is copied and synchronized across multiple database nodes.

intermediate

Explain master-slave replication.

In master-slave replication, one server (master) handles all writes and updates, while one or more servers (slaves) copy data from the master and handle read requests. This improves read performance and data backup.

intermediate

What is multi-master replication?

Multi-master replication allows multiple servers to accept write operations and synchronize changes with each other. This increases availability but requires conflict resolution to keep data consistent.

intermediate

Describe synchronous vs asynchronous replication.

Synchronous replication waits for data to be copied to all replicas before confirming a write, ensuring strong consistency but slower performance. Asynchronous replication confirms writes immediately and copies data later, improving speed but risking temporary inconsistency.

Which replication strategy allows multiple servers to accept writes simultaneously?

A Multi-master replication

B Master-slave replication

C Single-master replication

D Snapshot replication

Multi-master replication allows multiple servers to accept writes and synchronize changes.

In which replication type does the master server handle all write operations?

A Multi-master replication

B Peer-to-peer replication

C Master-slave replication

D Asynchronous replication

In master-slave replication, the master handles all writes.

What is a key advantage of asynchronous replication?

A Faster write performance

B Strong consistency

C No data conflicts

D Immediate data synchronization

Asynchronous replication improves write speed by not waiting for all replicas to confirm.

Which replication strategy is best for improving read performance by distributing read requests?

A Snapshot replication

B Multi-master replication

C Synchronous replication

D Master-slave replication

Master-slave replication distributes reads to slaves, improving read performance.

What is a challenge of multi-master replication?

A Single point of failure

B Conflict resolution

C Slow read operations

D No data backup

Multi-master replication requires conflict resolution to handle simultaneous writes.

Explain the differences between master-slave and multi-master replication strategies.

Think about how many servers can accept writes and how data conflicts are handled.

Describe the trade-offs between synchronous and asynchronous replication.

Consider speed versus data consistency.

Practice

1. Which replication strategy involves one main server handling all writes and one or more servers copying data from it?

easy

A. Master-Slave replication

B. Master-Master replication

C. Peer-to-Peer replication

D. Snapshot replication

Solution

1. Step 1: Understand Master-Slave replication

   In this strategy, one server (master) handles all write operations, and other servers (slaves) copy data from it.

2. Step 2: Compare with other strategies

   Master-Master allows multiple masters; Peer-to-Peer is decentralized; Snapshot copies data at intervals.

3. Final Answer:

   Master-Slave replication -> Option A

4. Quick Check:

   One main write server = Master-Slave [OK]

Hint: Master-Slave means one master writes, slaves copy [OK]

Common Mistakes:

• Confusing Master-Slave with Master-Master
• Thinking slaves can write data
• Mixing snapshot with continuous replication

2. Which of the following is the correct syntax to describe Master-Master replication?

easy

A. Two servers both accept writes and replicate changes to each other

B. One server writes, others read only

C. Data is copied only once at setup

D. Servers do not communicate

Solution

1. Step 1: Define Master-Master replication

   Both servers can accept writes and replicate changes to each other to keep data synchronized.

2. Step 2: Eliminate incorrect options

   Data is copied only once at setup describes snapshot; One server writes, others read only describes Master-Slave; Servers do not communicate is not replication.

3. Final Answer:

   Two servers both accept writes and replicate changes to each other -> Option A

4. Quick Check:

   Master-Master means both write and sync [OK]

Hint: Master-Master means both servers write and sync [OK]

Common Mistakes:

• Thinking only one server writes in Master-Master
• Confusing snapshot with replication
• Assuming no communication means replication

3. Consider a Master-Slave replication setup where the master server receives 100 write requests per second. If slaves replicate with a delay of 2 seconds, what is the expected delay in data consistency on slaves?

medium

A. Immediate consistency

B. No delay, slaves write directly

C. 2 seconds delay

D. 100 seconds delay

Solution

1. Step 1: Understand replication delay

   Slaves replicate data from master with a 2-second delay, so data on slaves lags behind master by 2 seconds.

2. Step 2: Analyze options

   Immediate consistency means no delay, which is incorrect. 100 seconds delay is unrelated to request rate. Slaves do not write directly.

3. Final Answer:

   2 seconds delay -> Option C

4. Quick Check:

   Replication delay = 2 seconds [OK]

Hint: Replication delay equals slave lag time [OK]

Common Mistakes:

• Confusing request rate with delay time
• Assuming slaves write directly
• Thinking slaves are always immediately consistent

4. A database administrator sets up Master-Master replication but notices data conflicts when both servers write the same record simultaneously. What is the best way to fix this?

medium

A. Allow only one server to write at a time without syncing

B. Switch to Master-Slave replication

C. Disable replication entirely

D. Implement conflict resolution rules or use timestamps

Solution

1. Step 1: Identify cause of conflicts

   Simultaneous writes cause conflicts in Master-Master replication because both servers can change the same data.

2. Step 2: Apply conflict resolution

   Using rules like timestamps or last-write-wins helps resolve conflicts automatically.

3. Final Answer:

   Implement conflict resolution rules or use timestamps -> Option D

4. Quick Check:

   Conflict resolution fixes simultaneous writes [OK]

Hint: Use conflict rules to fix Master-Master write clashes [OK]

Common Mistakes:

• Thinking disabling replication solves conflicts
• Switching to Master-Slave without need
• Ignoring conflict resolution mechanisms

5. You want a replication strategy that provides high availability and allows writes on multiple servers but can tolerate occasional conflicts. Which strategy fits best?

hard

A. Master-Slave replication

B. Master-Master replication

C. Snapshot replication

D. No replication

Solution

1. Step 1: Analyze requirements

   High availability and multiple write servers require a strategy where more than one server can accept writes.

2. Step 2: Match strategy to needs

   Master-Master replication allows multiple write servers but may have conflicts; Master-Slave does not allow multiple writes.

3. Final Answer:

   Master-Master replication -> Option B

4. Quick Check:

   Multiple writes + availability = Master-Master [OK]

Hint: Multiple write servers need Master-Master replication [OK]

Common Mistakes:

• Choosing Master-Slave for multiple writes
• Ignoring conflict tolerance
• Thinking snapshot replication supports writes