Why configuration matters in Redis - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is configuring maxmemory important in Redis?

Redis allows setting a maxmemory limit. What happens if you do not configure maxmemory in a Redis instance?

A Redis will automatically delete old keys to free memory without any configuration.

B Redis will use unlimited memory until the system runs out of RAM, possibly causing crashes.

C Redis refuses to start without a <code>maxmemory</code> setting.

D Redis will store data only on disk and not use RAM.

💡 Hint

Think about what happens when a program uses more memory than the system has.

If maxmemory is not set, Redis can consume all available RAM, which may cause the system to become unstable or crash. Setting maxmemory helps control memory usage.

❓ query_result

intermediate

What is the output of CONFIG GET maxmemory after setting it?

After running CONFIG SET maxmemory 1048576 in Redis, what will CONFIG GET maxmemory return?

Redis

CONFIG SET maxmemory 1048576
CONFIG GET maxmemory

A ["maxmemory", "1mb"]

B ["maxmemory", "0"]

C Error: maxmemory is read-only

D ["maxmemory", "1048576"]

💡 Hint

Remember Redis stores memory sizes in bytes internally.

Redis stores maxmemory as bytes. Setting it to 1048576 means 1MB. The CONFIG GET command returns the setting as a two-element array: the name and the value as a string.

📝 Syntax

advanced

Which CONFIG SET command correctly sets maxmemory-policy to allkeys-lru?

Choose the correct Redis command to set the eviction policy to allkeys-lru.

A CONFIG SET maxmemory-policy allkeys-lru

B CONFIG SET maxmemory_policy allkeys-lru

C CONFIG SET maxmemory policy allkeys-lru

D CONFIG SET maxmemory-policy='allkeys-lru'

💡 Hint

Redis configuration keys use hyphens, not underscores or spaces.

The correct syntax uses the exact configuration key name maxmemory-policy without spaces or underscores. Quotes or equals signs are not used in Redis commands.

❓ optimization

advanced

How does setting maxmemory-policy to volatile-lru affect Redis behavior?

If Redis is configured with maxmemory-policy volatile-lru, what happens when memory limit is reached?

A Redis evicts only keys with an expiration set, using least recently used order.

B Redis evicts any keys regardless of expiration, using least recently used order.

C Redis refuses to evict keys and returns errors on writes.

D Redis deletes keys randomly without considering expiration.

💡 Hint

Consider what 'volatile' means in Redis eviction policies.

The 'volatile-lru' policy evicts only keys that have an expiration set, choosing the least recently used among them. Keys without expiration are never evicted under this policy.

🔧 Debug

expert

Why does Redis reject CONFIG SET maxmemory 0 in some versions?

In some Redis versions, running CONFIG SET maxmemory 0 causes an error. Why?

A Because 0 disables maxmemory, which is invalid in those versions.

B Because 0 is interpreted as unlimited memory, which is not allowed.

C Because maxmemory must be set to a positive integer or -1 to disable.

D Because the command syntax requires quotes around 0.

💡 Hint

Check Redis documentation on valid maxmemory values.

Redis requires maxmemory to be a positive integer or -1 to disable the limit. Setting it to 0 is invalid and causes an error in some versions.