Replication strategies in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Master-Slave Replication

In a master-slave replication setup, what is the primary role of the slave database?

A To accept write operations and replicate changes to the master

B To act as a backup without any replication

C To accept both read and write operations independently

D To accept read operations and replicate changes from the master

💡 Hint

Think about which database handles writes and which handles reads in this setup.

In master-slave replication, the master handles write operations. The slave replicates data from the master and typically handles read operations to reduce load on the master.

📋 Factual

intermediate

Types of Replication Consistency

Which replication strategy ensures that all replicas have the exact same data at the same time before any transaction is considered committed?

A Synchronous replication

B Eventual consistency replication

C Semi-synchronous replication

D Asynchronous replication

💡 Hint

Consider which method waits for all replicas to confirm before completing a transaction.

Synchronous replication waits for all replicas to confirm the transaction before it is committed, ensuring strong consistency.

🔍 Analysis

advanced

Impact of Replication Lag

What is the most likely consequence of replication lag in an asynchronous replication system?

A Data on replicas is always up to date with the master

B Write operations are blocked until replicas confirm

C Read queries on replicas may return stale data

D The master database becomes read-only

💡 Hint

Think about what happens when replicas receive updates later than the master.

Replication lag means replicas receive updates after some delay, so read queries on replicas might return outdated data.

❓ Comparison

advanced

Comparing Multi-Master and Master-Slave Replication

Which of the following is a key difference between multi-master and master-slave replication?

A Master-slave replication supports conflict resolution; multi-master does not

B Multi-master allows writes on multiple nodes; master-slave allows writes only on the master

C Multi-master replication does not replicate data; master-slave replicates data

D Master-slave replication requires all nodes to be writable

💡 Hint

Consider which replication type allows multiple nodes to accept write operations.

Multi-master replication allows multiple nodes to accept writes and synchronize changes, while master-slave restricts writes to the master only.

❓ Reasoning

expert

Choosing Replication Strategy for High Availability

You need a replication strategy that minimizes downtime and data loss during a master failure in a distributed database. Which strategy best fits this requirement?

A Synchronous multi-master replication

B Asynchronous master-slave replication

C Asynchronous multi-master replication

D Single master with no replication

💡 Hint

Think about which strategy ensures data consistency and availability even if one master fails.

Synchronous multi-master replication allows multiple masters to be active and keeps data consistent, minimizing downtime and data loss if one master fails.

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