Eviction policies overview in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the Redis eviction policy to remove the least recently used keys.

Redis

CONFIG SET maxmemory-policy [1]

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

Aallkeys-lru

Bnoeviction

Callkeys-random

Dvolatile-ttl

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'noeviction' which disables eviction.

Choosing 'volatile-ttl' which only evicts keys with expiration.

The allkeys-lru policy evicts the least recently used keys when memory limit is reached.

2fill in blank

medium

Complete the code to set Redis to evict only keys with an expiration time using a random eviction policy.

Redis

CONFIG SET maxmemory-policy [1]

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

Aallkeys-lfu

Ballkeys-random

Cvolatile-random

Dvolatile-lru

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'allkeys-random' which evicts any key randomly.

Choosing 'volatile-lru' which evicts least recently used keys with expiration.

The volatile-random policy evicts random keys but only those with an expiration set.

3fill in blank

hard

Fix the error in the command to set Redis eviction policy to remove the least frequently used keys among all keys.

Redis

CONFIG SET maxmemory-policy [1]

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

Aallkeys-lfu

Ballkeys-lru

Cvolatile-lfu

Dnoeviction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'volatile-lfu' which only evicts keys with expiration.

Using 'noeviction' which disables eviction.

The allkeys-lfu policy evicts the least frequently used keys regardless of expiration.

4fill in blank

hard

Fill both blanks to set Redis to evict keys randomly but only those with expiration time.

Redis

CONFIG SET maxmemory-policy [1]
CONFIG SET maxmemory [2]

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

Avolatile-random

Ballkeys-lru

C100mb

Dnoeviction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'noeviction' as policy which disables eviction.

Setting maxmemory to a non-size value.

Setting volatile-random evicts random keys with expiration, and setting maxmemory to 100mb limits memory usage.

5fill in blank

hard

Fill all three blanks to configure Redis to evict the least recently used keys among all keys and set maxmemory to 50mb.

Redis

CONFIG SET maxmemory-policy [1]
CONFIG SET maxmemory [2]
CONFIG SET [3] 5

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

Aallkeys-lru

B50mb

Cmaxmemory-samples

Dnoeviction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'noeviction' disables eviction.

Forgetting to set maxmemory or setting it incorrectly.

allkeys-lru evicts least recently used keys, 50mb sets the memory limit, and maxmemory-samples controls how many keys Redis samples to decide eviction candidates.

Practice

1. What is the main purpose of eviction policies in Redis?

easy

A. To encrypt Redis data

B. To configure the network settings of Redis

C. To backup data automatically

D. To decide how Redis frees memory when it is full

Solution

1. Step 1: Understand Redis memory management

   Redis uses eviction policies to manage memory when it reaches its limit.

2. Step 2: Identify the role of eviction policies

   Eviction policies decide which data to remove to free memory and keep Redis running smoothly.

3. Final Answer:

   To decide how Redis frees memory when it is full -> Option D

4. Quick Check:

   Eviction policies control memory freeing = A [OK]

Hint: Eviction policies manage memory freeing in Redis [OK]

Common Mistakes:

• Confusing eviction policies with backup or encryption
• Thinking eviction policies configure network
• Assuming eviction policies handle data encryption

2. Which command correctly sets the eviction policy to 'allkeys-lru' in Redis?

easy

A. CONFIG SET maxmemory-policy allkeys-lru

B. SET maxmemory-policy allkeys-lru

C. CONFIG GET maxmemory-policy allkeys-lru

D. EVICT POLICY allkeys-lru

Solution

1. Step 1: Recall the correct command format

   Redis uses CONFIG SET to change configuration settings.

2. Step 2: Match the correct syntax for eviction policy

   The correct syntax is CONFIG SET maxmemory-policy policy_name, so allkeys-lru fits here.

3. Final Answer:

   CONFIG SET maxmemory-policy allkeys-lru -> Option A

4. Quick Check:

   Use CONFIG SET for eviction policy = A [OK]

Hint: Use CONFIG SET maxmemory-policy to set eviction [OK]

Common Mistakes:

• Using SET instead of CONFIG SET
• Using CONFIG GET to set a value
• Using a non-existent EVICT POLICY command

3. Given Redis is set with eviction policy volatile-lru and maxmemory is reached, which keys are eligible for eviction?

medium

A. All keys regardless of expiration

B. Only keys with an expiration set

C. Only keys without expiration

D. No keys are evicted automatically

Solution

1. Step 1: Understand 'volatile-lru' policy meaning

   This policy evicts keys with expiration set using least recently used (LRU) order.

2. Step 2: Identify which keys can be evicted

   Only keys that have an expiration time are considered for eviction under 'volatile-lru'. Keys without expiration stay safe.

3. Final Answer:

   Only keys with an expiration set -> Option B

4. Quick Check:

   volatile-lru evicts expiring keys = B [OK]

Hint: volatile-lru evicts only keys with expiration [OK]

Common Mistakes:

• Thinking all keys are evicted
• Confusing volatile-lru with allkeys-lru
• Assuming no keys are evicted automatically

4. You set Redis eviction policy to noeviction but Redis still evicts keys when memory is full. What is the likely cause?

medium

A. The policy was not applied correctly or Redis was restarted without saving config

B. Redis always evicts keys regardless of policy

C. noeviction policy evicts keys randomly

D. Redis ignores eviction policies when maxmemory is set

Solution

1. Step 1: Understand 'noeviction' policy behavior

   This policy prevents Redis from evicting keys automatically when memory is full.

2. Step 2: Identify why eviction still happens

   If eviction occurs, likely the policy was not saved or applied properly, or Redis restarted without config persistence.

3. Final Answer:

   The policy was not applied correctly or Redis was restarted without saving config -> Option A

4. Quick Check:

   noeviction means no eviction unless misconfigured = C [OK]

Hint: Check config save and apply for noeviction policy [OK]

Common Mistakes:

• Believing Redis always evicts keys
• Thinking noeviction evicts randomly
• Assuming eviction policies are ignored when maxmemory is set

5. You want Redis to evict the least recently used keys regardless of expiration when memory is full. Which eviction policy should you choose?

hard

A. volatile-lru

B. noeviction

C. allkeys-lru

D. volatile-random

Solution

1. Step 1: Understand eviction policy options

   volatile-lru evicts only keys with expiration; allkeys-lru evicts any key using LRU.

2. Step 2: Match requirement to policy

   Since eviction should ignore expiration and evict least recently used keys, allkeys-lru fits best.

3. Final Answer:

   allkeys-lru -> Option C

4. Quick Check:

   Evict any key LRU = allkeys-lru = D [OK]

Hint: allkeys-lru evicts any key by least recent use [OK]

Common Mistakes:

• Choosing volatile-lru which only evicts expiring keys
• Selecting volatile-random which evicts randomly
• Picking noeviction which disables eviction