EVALSHA for cached scripts in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis EVALSHA command?

Given the Lua script SHA1 hash is abcd1234 and the script returns the sum of two keys' integer values, what will be the output of this command if key1=5 and key2=3?

Redis

EVALSHA abcd1234 2 key1 key2

A TypeError

B 8

C Error: NOSCRIPT No matching script. Please use EVAL.

D 5 3

💡 Hint

EVALSHA runs a cached Lua script by its SHA1 hash and returns the script's result.

The script sums the integer values of key1 and key2, which are 5 and 3, so the output is 8.

🧠 Conceptual

intermediate

Why use EVALSHA instead of EVAL in Redis?

Choose the best reason why Redis clients prefer using EVALSHA over EVAL after the script is loaded.

A EVALSHA is faster because it uses the cached script by its SHA1 hash, avoiding re-sending the script code.

B EVALSHA can run scripts without any keys or arguments.

C EVALSHA automatically updates the script if it changes on the server.

D EVALSHA returns the script source code instead of executing it.

💡 Hint

Think about network efficiency and script caching.

EVALSHA uses the cached script identified by its SHA1 hash, so it avoids sending the full script code every time, making it faster.

📝 Syntax

advanced

Which EVALSHA command syntax is correct to run a script with 3 keys and 2 arguments?

Select the correct Redis EVALSHA command syntax to run a cached script with SHA1 hash f1e2d3c4, passing 3 keys and 2 arguments.

A EVALSHA f1e2d3c4 5 key1 key2 key3 arg1 arg2

B EVALSHA f1e2d3c4 key1 key2 key3 3 arg1 arg2

C EVALSHA f1e2d3c4 3 key1 key2 key3 arg1 arg2

D EVALSHA f1e2d3c4 2 key1 key2 key3 arg1 arg2

💡 Hint

Remember the syntax: EVALSHA ... ...

The second argument is the number of keys (3), followed by the keys, then the arguments.

🔧 Debug

advanced

What error occurs if you run EVALSHA with an unknown SHA1 hash?

You run EVALSHA deadbeef 1 key1 arg1 but the script is not cached on the server. What error message will Redis return?

A SyntaxError: invalid command

B OK

C TypeError: missing arguments

D Error: NOSCRIPT No matching script. Please use EVAL.

💡 Hint

Think about what happens when the script is not found in cache.

Redis returns a NOSCRIPT error indicating the script is not cached and suggests using EVAL to load it.

❓ optimization

expert

How to optimize repeated Lua script execution in Redis using EVALSHA?

You have a Lua script that you run many times with different keys and arguments. Which approach best optimizes performance?

A Load the script once with EVAL, then run it repeatedly with EVALSHA using the cached SHA1 hash.

B Run the script every time with EVAL to ensure the latest version is used.

C Use EVALSHA without loading the script first; Redis will auto-load it.

D Store the script in a Redis string and call it by GET command.

💡 Hint

Consider network traffic and script caching benefits.

Loading the script once with EVAL caches it on the server. Subsequent calls with EVALSHA use the cached script, reducing network overhead and improving speed.