Eviction policies overview in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Redis eviction policy: noeviction

What happens when Redis reaches its max memory limit and the eviction policy is set to noeviction?

A Redis increases its memory limit dynamically to accommodate new data.

B Redis removes the least recently used keys automatically to free memory.

C Redis removes random keys to free memory and continues accepting writes.

D Redis stops accepting writes and returns an error until memory is freed.

💡 Hint

Think about what 'no eviction' means for memory management.

With the noeviction policy, Redis refuses write commands when max memory is reached, returning an error. It does not remove any keys automatically.

❓ query_result

intermediate

Result of keys removed with allkeys-lru policy

Assume Redis has maxmemory set and eviction policy allkeys-lru. The database contains keys with varying last access times. Which keys will Redis remove first when memory is full?

A Random keys without considering access time or expiration.

B Only keys with an expiration time that are closest to expiring.

C Keys that were accessed least recently, regardless of expiration.

D Keys that were added most recently to the database.

💡 Hint

LRU means 'Least Recently Used'.

The allkeys-lru policy evicts the least recently used keys from all keys, ignoring expiration times.

📝 Syntax

advanced

Correct Redis config command for volatile-lfu eviction

Which Redis configuration command correctly sets the eviction policy to volatile-lfu?

A CONFIG SET maxmemory-policy volatile-lfu

B CONFIG SET eviction-policy volatile-lfu

C SET maxmemory-policy volatile-lfu

D CONFIG GET maxmemory volatile-lfu

💡 Hint

Check the exact syntax for setting maxmemory policy in Redis.

The correct command to set eviction policy is CONFIG SET maxmemory-policy followed by the policy name.

❓ optimization

advanced

Choosing eviction policy for frequently accessed keys with expiration

You have a Redis cache with many keys that have expiration times and are accessed frequently. You want to optimize memory usage by evicting keys that are least frequently used but only among keys with expiration set. Which eviction policy should you choose?

A allkeys-lru

B volatile-lfu

C volatile-random

D noeviction

💡 Hint

Focus on eviction policies that consider frequency and expiration.

volatile-lfu evicts the least frequently used keys but only among keys with expiration set, which fits the requirement.

🔧 Debug

expert

Why does Redis evict keys unexpectedly with allkeys-random?

A Redis instance is configured with maxmemory and eviction policy allkeys-random. Unexpectedly, keys that are still frequently accessed are being evicted. Why does this happen?

A Because allkeys-random evicts keys randomly without considering usage or expiration.

B Because Redis evicts keys based on least recently used order in allkeys-random.

C Because the maxmemory setting is ignored when eviction policy is allkeys-random.

D Because Redis evicts only expired keys first, ignoring the policy.

💡 Hint

Think about what 'random' means in eviction context.

The allkeys-random policy evicts keys randomly from all keys, so even frequently accessed keys can be removed.