Script loading and caching in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of SCRIPT LOAD command

What does the SCRIPT LOAD command return when you load a Lua script into Redis?

Redis

SCRIPT LOAD "return redis.call('PING')"

A An integer representing the number of commands in the script

B A SHA1 hash string representing the loaded script

C The output of the script execution, e.g., 'PONG'

D The string 'OK' indicating the script loaded successfully

💡 Hint

Think about what Redis returns to identify a script uniquely after loading.

SCRIPT LOAD returns the SHA1 hash of the script, which can be used later to execute the script by reference.

❓ query_result

intermediate

Result of EVALSHA with missing script

What happens when you run EVALSHA with a SHA1 hash that is not loaded in Redis?

Redis

EVALSHA <nonexistent_sha1> 0

A Redis returns an error indicating the script is not found

B Redis automatically loads the script from the last executed scripts

C Redis returns nil without error

D Redis executes the script anyway by fetching it from disk

💡 Hint

Consider what Redis does if the script hash is unknown.

If the script SHA1 is not found in Redis cache, EVALSHA returns a NOSCRIPT error.

📝 Syntax

advanced

Identify the correct SCRIPT FLUSH usage

Which of the following commands correctly flushes all cached Lua scripts in Redis?

A SCRIPT DELETE ALL

B SCRIPT CLEAR

C SCRIPT FLUSH

D SCRIPT REMOVE

💡 Hint

Check the official Redis command for clearing scripts.

SCRIPT FLUSH clears all cached scripts from Redis memory.

❓ optimization

advanced

Best practice for script execution performance

To optimize performance when running the same Lua script multiple times in Redis, which approach is best?

A Use MULTI/EXEC transactions to run the script multiple times

B Run the script each time with EVAL to avoid caching issues

C Store the script in a Redis key and retrieve it before each execution

D Load the script once with SCRIPT LOAD, then run it multiple times with EVALSHA

💡 Hint

Think about how Redis caches scripts and how to reuse them efficiently.

Loading the script once and running it by SHA1 hash avoids repeated parsing and improves performance.

🧠 Conceptual

expert

Understanding script caching behavior on Redis restart

What happens to cached Lua scripts in Redis after a server restart?

A All cached scripts are lost and must be reloaded

B Cached scripts persist automatically across restarts

C Scripts are saved to disk and reloaded on startup

D Scripts remain cached if Redis is configured with AOF persistence

💡 Hint

Consider Redis memory and persistence behavior for scripts.

Cached scripts are stored in memory only and are lost on restart; they must be reloaded.