REPLICAOF command in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the REPLICAOF command do in Redis?

It makes the current Redis server a replica of another Redis server by specifying the master server's IP and port.

beginner

How do you stop a Redis server from being a replica using REPLICAOF?

Use REPLICAOF NO ONE to make the Redis server stop replicating and become a master again.

beginner

Syntax of the REPLICAOF command?

REPLICAOF <masterip> <masterport>

or

REPLICAOF NO ONE

to stop replication.

intermediate

What happens to the data on a Redis server when you run REPLICAOF <masterip> <masterport>?

The server clears its current data and starts syncing data from the specified master server.

intermediate

Can a Redis server be a replica of multiple masters at the same time using REPLICAOF?

No, a Redis server can only replicate from one master at a time.

What command makes a Redis server stop replicating and become a master again?

A MASTEROF NO ONE

B REPLICAOF 127.0.0.1 6379

C SLAVEOF NO ONE

D REPLICAOF NO ONE

The command REPLICAOF NO ONE stops replication and makes the server a master.

What does the REPLICAOF command require as arguments?

A Database name and password

B Replica name and port

C Master IP and port

D User and password

REPLICAOF needs the master server's IP address and port number.

If you run REPLICAOF 192.168.1.10 6379, what happens?

A The server becomes a replica of the master at 192.168.1.10:6379

B The server becomes a master

C The server deletes all data permanently

D The server restarts

This command makes the server replicate data from the specified master.

Can a Redis server replicate from two masters at the same time?

A Yes, up to two masters

B No, only one master at a time

C Yes, unlimited masters

D Only if configured in cluster mode

Redis supports replication from only one master per replica server.

Which Redis command was previously used instead of REPLICAOF?

A SLAVEOF

B MASTEROF

C FOLLOW

D SYNC

SLAVEOF was the old name for REPLICAOF.

Explain how the REPLICAOF command is used to set up replication in Redis.

Think about how a server becomes a replica and how it can stop replicating.

Describe what happens internally when a Redis server runs REPLICAOF <masterip> <masterport>.

Consider the data and role changes on the server.

Practice

1. What does the REPLICAOF command do in Redis?

easy

A. It resets the Redis server to factory settings.

B. It deletes all data from the Redis server.

C. It creates a backup file of the Redis database.

D. It makes the Redis server copy data from another Redis server.

Solution

1. Step 1: Understand the purpose of REPLICAOF

   The REPLICAOF command is used to set a Redis server as a replica, meaning it copies data from a master server.

2. Step 2: Compare options with the command's function

   Only It makes the Redis server copy data from another Redis server. correctly describes this behavior. Other options describe unrelated actions.

3. Final Answer:

   It makes the Redis server copy data from another Redis server. -> Option D

4. Quick Check:

   REPLICAOF copies data = A [OK]

Hint: REPLICAOF means 'copy from another server' [OK]

Common Mistakes:

• Confusing REPLICAOF with backup commands
• Thinking it deletes data
• Assuming it resets server settings

2. Which of the following is the correct syntax to stop replication and make a Redis server standalone?

easy

A. REPLICAOF NO ONE

B. REPLICAOF NONE

C. REPLICAOF STOP

D. REPLICAOF DISABLE

Solution

1. Step 1: Recall the exact syntax to stop replication

   The correct command to stop replication is REPLICAOF NO ONE.

2. Step 2: Verify other options

   Options A, B, and D are invalid Redis commands for stopping replication.

3. Final Answer:

   REPLICAOF NO ONE -> Option A

4. Quick Check:

   Stop replication = REPLICAOF NO ONE [OK]

Hint: Use 'NO ONE' exactly to stop replication [OK]

Common Mistakes:

• Using 'NONE' instead of 'NO ONE'
• Trying 'STOP' or 'DISABLE' which are invalid
• Missing the space between REPLICAOF and NO ONE

3. If you run REPLICAOF 192.168.1.10 6379 on a Redis server, what will happen?

medium

A. The server will become a replica and copy data from the server at 192.168.1.10 port 6379.

B. The server will delete all data and stop working.

C. The server will create a backup of the server at 192.168.1.10.

D. The server will reject the command with a syntax error.

Solution

1. Step 1: Understand the REPLICAOF command with IP and port

   Running REPLICAOF 192.168.1.10 6379 sets the server as a replica of the specified IP and port.

2. Step 2: Check other options for correctness

   Options B and C describe unrelated actions. The server will reject the command with a syntax error. is incorrect because the syntax is valid.

3. Final Answer:

   The server will become a replica and copy data from the server at 192.168.1.10 port 6379. -> Option A

4. Quick Check:

   REPLICAOF IP PORT = replica mode [OK]

Hint: IP and port after REPLICAOF set replica source [OK]

Common Mistakes:

• Thinking it deletes data
• Assuming it creates backups
• Believing the syntax is invalid

4. You tried to run REPLICAOF NOONE to stop replication, but it failed. What is the error?

medium

A. The command should be REPLICAOF NONE instead.

B. You need to restart the Redis server before stopping replication.

C. The command is missing a space; it should be REPLICAOF NO ONE.

D. The command is correct; the failure is due to network issues.

Solution

1. Step 1: Identify the syntax error in the command

   The command REPLICAOF NOONE is invalid because it lacks a space between NO and ONE.

2. Step 2: Confirm the correct syntax

   The correct command is REPLICAOF NO ONE. Other options are incorrect because they suggest wrong commands or unrelated issues.

3. Final Answer:

   The command is missing a space; it should be REPLICAOF NO ONE. -> Option C

4. Quick Check:

   Correct stop syntax = REPLICAOF NO ONE [OK]

Hint: Remember space between NO and ONE to stop replication [OK]

Common Mistakes:

• Writing NOONE as one word
• Using NONE instead of NO ONE
• Assuming restart is needed to stop replication

5. You want to set up a Redis replica for backup but also want to stop replication temporarily without losing data. Which sequence of commands should you use?

hard

A. Run REPLICAOF NO ONE first, then REPLICAOF 192.168.1.20 6379 to start replication.

B. First run REPLICAOF 192.168.1.20 6379 to start replication, then REPLICAOF NO ONE to stop it temporarily.

C. Run REPLICAOF STOP to pause replication, then REPLICAOF START to resume.

D. Use REPLICAOF DISABLE to stop replication and REPLICAOF ENABLE to start it again.

Solution

1. Step 1: Understand how to start replication

   Use REPLICAOF IP PORT to start replication from a master server.

2. Step 2: Understand how to stop replication temporarily

   Use REPLICAOF NO ONE to stop replication without deleting data or resetting the server.

3. Step 3: Evaluate options

   First run REPLICAOF 192.168.1.20 6379 to start replication, then REPLICAOF NO ONE to stop it temporarily. correctly shows starting replication then stopping it temporarily. Options C and D use invalid commands. Run REPLICAOF NO ONE first, then REPLICAOF 192.168.1.20 6379 to start replication. reverses the order, which is less logical for setup.

4. Final Answer:

   First run REPLICAOF 192.168.1.20 6379 to start replication, then REPLICAOF NO ONE to stop it temporarily. -> Option B

5. Quick Check:

   Start with IP, stop with NO ONE [OK]

Hint: Start replica with IP, stop with NO ONE command [OK]

Common Mistakes:

• Using invalid commands like STOP or DISABLE
• Stopping replication before starting it
• Thinking stopping deletes data