Maxmemory setting in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of the command to check maxmemory?

You run the Redis command CONFIG GET maxmemory. What is the expected output format?

Redis

CONFIG GET maxmemory

A ["maxmemory"]

B "maxmemory 0"

C ["maxmemory", "0"]

D 0

💡 Hint

Remember Redis returns configuration as an array with key and value.

The CONFIG GET command returns an array with the parameter name and its value as strings.

🧠 Conceptual

intermediate

What happens if maxmemory is set to 0 in Redis?

In Redis, if you set maxmemory to 0, what does it mean for memory usage?

A Redis has no memory limit and can use all available memory.

B Redis will limit memory usage to 0 bytes and refuse writes.

C Redis will use a default memory limit of 100MB.

D Redis will automatically evict keys when memory reaches 0.

💡 Hint

Think about what zero means as a limit.

Setting maxmemory to 0 disables memory limits, so Redis can use all available memory.

📝 Syntax

advanced

Which command correctly sets maxmemory to 100 megabytes?

Choose the correct Redis command to set maxmemory to 100MB.

A CONFIG SET maxmemory 100000000

B CONFIG SET maxmemory 100MB

C CONFIG SET maxmemory 100mb

D CONFIG SET maxmemory 104857600

💡 Hint

Redis expects maxmemory in bytes, not with units.

Redis requires maxmemory value in bytes, so 100MB = 100 * 1024 * 1024 = 104857600 bytes.

❓ optimization

advanced

How to configure Redis to evict least recently used keys when maxmemory is reached?

You want Redis to remove least recently used keys automatically when memory limit is reached. Which command sets this behavior?

A CONFIG SET maxmemory-policy volatile-lru

B CONFIG SET maxmemory-policy allkeys-lru

C CONFIG SET maxmemory-policy noeviction

D CONFIG SET maxmemory-policy allkeys-random

💡 Hint

Look for a policy that evicts any key based on usage.

The allkeys-lru policy evicts the least recently used keys from all keys when memory is full.

🔧 Debug

expert

Why does Redis not evict keys despite maxmemory being set and policy configured?

You set maxmemory to 50MB and maxmemory-policy to allkeys-lru, but Redis never evicts keys and memory usage grows beyond 50MB. What is the most likely cause?

A The maxmemory-policy setting is ignored if maxmemory is zero or not set properly.

B Eviction only happens if keys have expiration times set.

C Redis only evicts keys when memory usage reaches maxmemory plus a safety margin.

D The maxmemory setting is not applied because Redis was not restarted.

💡 Hint

Check if maxmemory is properly set and non-zero.

If maxmemory is zero or not set properly, eviction policies are ignored and Redis won't evict keys.