Why configuration matters in Redis - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the maximum memory limit in Redis configuration.

Redis

CONFIG SET maxmemory [1]

Drag options to blanks, or click blank then click option'

A100mb

Bmaxmemory

Ctimeout

Dappendonly

Attempts:

3 left

💡 Hint

Common Mistakes

Using a configuration name instead of a value.

Using a command name instead of a memory size.

The maxmemory setting controls the maximum memory Redis can use. Setting it to 100mb limits Redis to 100 megabytes.

2fill in blank

medium

Complete the code to enable AOF persistence in Redis.

Redis

CONFIG SET [1] yes

Drag options to blanks, or click blank then click option'

Asave

Bappendonly

Crdbcompression

Dmaxclients

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing 'save' with enabling appendonly.

Using numeric values instead of 'yes' or 'no'.

The appendonly setting enables AOF persistence, which logs every write operation. Setting it to yes turns it on.

3fill in blank

hard

Fix the error in the command to set the eviction policy to 'allkeys-lru'.

Redis

CONFIG SET maxmemory-policy [1]

Drag options to blanks, or click blank then click option'

Aallkeys-lru

Bnoeviction

Cvolatile-random

Drandom

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'noeviction' which disables eviction.

Choosing policies that only evict volatile keys.

The maxmemory-policy setting controls how Redis evicts keys when memory is full. allkeys-lru evicts the least recently used keys from all keys.

4fill in blank

hard

Fill both blanks to configure Redis to save snapshots every 60 seconds if at least 1000 keys changed.

Redis

CONFIG SET save "[1] [2]"

Drag options to blanks, or click blank then click option'

A60

B1000

C900

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the time and keys values.

Using too large or too small numbers.

The save setting defines snapshot intervals. 60 1000 means save if 1000 keys changed in 60 seconds.

5fill in blank

hard

Fill all three blanks to configure Redis to disable AOF, set max clients to 500, and set timeout to 300 seconds.

Redis

CONFIG SET appendonly [1]
CONFIG SET maxclients [2]
CONFIG SET timeout [3]

Drag options to blanks, or click blank then click option'

Ayes

B500

C300

Dno

Attempts:

3 left

💡 Hint

Common Mistakes

Setting appendonly to 'yes' instead of 'no'.

Using wrong numbers for maxclients or timeout.

Setting appendonly to no disables AOF persistence. maxclients limits client connections to 500. timeout sets idle client timeout to 300 seconds.

Practice

1. Why is it important to configure Redis properly before using it in a project?

easy

A. Because configuration is only needed for security reasons

B. Because Redis does not work without configuration files

C. Because configuration files store the data permanently

D. Because configuration controls how Redis behaves and performs

Solution

1. Step 1: Understand Redis configuration role

   Redis configuration sets how Redis behaves and performs, affecting speed and features.

2. Step 2: Evaluate the options

   Only Because configuration controls how Redis behaves and performs correctly states the importance of configuration controlling behavior and performance.

3. Final Answer:

   Because configuration controls how Redis behaves and performs -> Option D

4. Quick Check:

   Configuration controls behavior = A [OK]

Hint: Remember: configuration shapes Redis behavior and speed [OK]

Common Mistakes:

• Thinking Redis won't work without config files
• Confusing configuration with data storage
• Assuming config is only for security

2. Which of the following is the correct Redis command to check the current value of a configuration setting?

easy

A. GET CONFIG <setting_name>

B. CONFIG SET <setting_name>

C. CONFIG GET <setting_name>

D. SET CONFIG <setting_name>

Solution

1. Step 1: Recall Redis commands for configuration

   To check a setting, Redis uses CONFIG GET followed by the setting name.

2. Step 2: Identify correct syntax

   Only CONFIG GET <setting_name> uses the correct command and order: CONFIG GET <setting_name>.

3. Final Answer:

   CONFIG GET <setting_name> -> Option C

4. Quick Check:

   Check config with CONFIG GET = A [OK]

Hint: Use CONFIG GET to view settings, CONFIG SET to change [OK]

Common Mistakes:

• Mixing up GET and SET commands
• Using wrong command order
• Assuming GET CONFIG is valid

3. Given the Redis commands below, what will be the output of CONFIG GET maxmemory after running them?

CONFIG SET maxmemory 100mb
CONFIG SET maxmemory-policy allkeys-lru
CONFIG GET maxmemory

medium

A. Error: Invalid command

B. ["maxmemory", "100mb"]

C. ["maxmemory-policy", "allkeys-lru"]

D. ["maxmemory", "0"]

Solution

1. Step 1: Understand the commands executed

   The first command sets maxmemory to 100mb, the second sets eviction policy, the third retrieves maxmemory.

2. Step 2: Predict output of CONFIG GET maxmemory

   CONFIG GET returns the setting name and its current value, so it returns ["maxmemory", "100mb"].

3. Final Answer:

   ["maxmemory", "100mb"] -> Option B

4. Quick Check:

   CONFIG GET maxmemory = ["maxmemory", "100mb"] [OK]

Hint: CONFIG GET returns setting name and current value as array [OK]

Common Mistakes:

• Expecting policy value from maxmemory GET
• Assuming default 0 value after set
• Thinking command causes error

4. You run the command CONFIG SET maxmemory 500mb but Redis returns an error. What is the most likely cause?

medium

A. The maxmemory value is too large for the server's available memory

B. The command syntax is incorrect

C. Redis does not support maxmemory configuration

D. You must restart Redis before changing maxmemory

Solution

1. Step 1: Analyze the error cause for CONFIG SET maxmemory

   Redis may reject setting maxmemory if the value exceeds available system memory.

2. Step 2: Check other options for validity

   Syntax is correct, Redis supports maxmemory, and restart is not required for this setting.

3. Final Answer:

   The maxmemory value is too large for the server's available memory -> Option A

4. Quick Check:

   Memory limit too high causes error = B [OK]

Hint: Check server memory before setting maxmemory [OK]

Common Mistakes:

• Assuming syntax error without checking
• Thinking Redis lacks maxmemory setting
• Believing restart is always needed

5. You want Redis to automatically remove least recently used keys when memory is full. Which configuration changes should you apply?

hard

A. CONFIG SET maxmemory 200mb and CONFIG SET maxmemory-policy allkeys-lru

B. CONFIG SET maxmemory 0 and CONFIG SET maxmemory-policy noeviction

C. CONFIG SET maxmemory 200mb and CONFIG SET maxmemory-policy volatile-ttl

D. CONFIG SET maxmemory 0 and CONFIG SET maxmemory-policy volatile-lru

Solution

1. Step 1: Identify the desired behavior

   You want Redis to evict least recently used keys from all keys when memory is full.

2. Step 2: Match configuration to behavior

   Setting maxmemory to a limit (e.g., 200mb) enables memory limit. Setting maxmemory-policy to allkeys-lru evicts least recently used keys from all keys.

3. Step 3: Evaluate other options

   Options with maxmemory 0 disable memory limit. Policies like noeviction or volatile-ttl do not evict all keys LRU.

4. Final Answer:

   CONFIG SET maxmemory 200mb and CONFIG SET maxmemory-policy allkeys-lru -> Option A

5. Quick Check:

   Set memory limit + allkeys-lru policy = C [OK]

Hint: Set maxmemory limit and allkeys-lru policy for LRU eviction [OK]

Common Mistakes:

• Setting maxmemory to 0 disables eviction
• Choosing wrong eviction policy
• Confusing volatile and allkeys policies