MSET and MGET for bulk operations in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this MGET command?

Given the following Redis commands executed in order:

1. MSET user:1 "Alice" user:2 "Bob" user:3 "Charlie"
2. MGET user:1 user:2 user:4

What is the output of the MGET command?

Redis

MSET user:1 "Alice" user:2 "Bob" user:3 "Charlie"
MGET user:1 user:2 user:4

A ["Alice", "Bob", null]

B ["Alice", "Bob", ""]

C ["Alice", "Bob", "Charlie"]

D [null, null, null]

💡 Hint

MGET returns values for keys in order; missing keys return null.

MGET returns the values for the requested keys in the same order. Since user:4 does not exist, its value is null.

📝 Syntax

intermediate

Which MSET command is syntactically correct?

Choose the syntactically correct MSET command to set keys 'a' to '1' and 'b' to '2'.

A MSET [a,1,b,2]

B MSET {a:1, b:2}

C MSET (a=1, b=2)

D MSET a 1 b 2

💡 Hint

MSET expects key and value pairs as separate arguments.

MSET requires keys and values as separate arguments, not as objects or arrays.

❓ optimization

advanced

Why use MSET instead of multiple SET commands?

Which is the main advantage of using MSET over multiple individual SET commands in Redis?

A MSET encrypts keys and values for security.

B MSET executes all sets atomically and reduces network overhead.

C MSET allows setting keys with expiration times.

D MSET automatically compresses values to save memory.

💡 Hint

Think about network calls and atomicity.

MSET sends all key-value pairs in one command, reducing network round-trips and ensuring atomicity.

🔧 Debug

advanced

Identify the error in this MGET usage

What error occurs when running this command?

MGET user:1 user:2 user:3 user:4 user:5 user:6 user:7 user:8 user:9 user:10 user:11 user:12 user:13 user:14 user:15 user:16 user:17 user:18 user:19 user:20 user:21 user:22 user:23 user:24 user:25 user:26 user:27 user:28 user:29 user:30 user:31 user:32 user:33 user:34 user:35 user:36 user:37 user:38 user:39 user:40 user:41 user:42 user:43 user:44 user:45 user:46 user:47 user:48 user:49 user:50 user:51 user:52 user:53 user:54 user:55 user:56 user:57 user:58 user:59 user:60 user:61 user:62 user:63 user:64 user:65 user:66 user:67 user:68 user:69 user:70 user:71 user:72 user:73 user:74 user:75 user:76 user:77 user:78 user:79 user:80 user:81 user:82 user:83 user:84 user:85 user:86 user:87 user:88 user:89 user:90 user:91 user:92 user:93 user:94 user:95 user:96 user:97 user:98 user:99 user:100 user:101

Redis

MGET user:1 user:2 user:3 user:4 user:5 user:6 user:7 user:8 user:9 user:10 user:11 user:12 user:13 user:14 user:15 user:16 user:17 user:18 user:19 user:20 user:21 user:22 user:23 user:24 user:25 user:26 user:27 user:28 user:29 user:30 user:31 user:32 user:33 user:34 user:35 user:36 user:37 user:38 user:39 user:40 user:41 user:42 user:43 user:44 user:45 user:46 user:47 user:48 user:49 user:50 user:51 user:52 user:53 user:54 user:55 user:56 user:57 user:58 user:59 user:60 user:61 user:62 user:63 user:64 user:65 user:66 user:67 user:68 user:69 user:70 user:71 user:72 user:73 user:74 user:75 user:76 user:77 user:78 user:79 user:80 user:81 user:82 user:83 user:84 user:85 user:86 user:87 user:88 user:89 user:90 user:91 user:92 user:93 user:94 user:95 user:96 user:97 user:98 user:99 user:100 user:101

A Returns null for keys beyond 100

B Error: MGET supports a maximum of 100 keys per call

C No error, returns values for all keys

D SyntaxError: Too many arguments for MGET

💡 Hint

Redis MGET has no hard limit of 100 keys; it is limited practically by memory, network buffers, and performance considerations.

Redis MGET supports more than 100 keys per call. There is no error for 101 keys; it returns an array with values or null for each key in order.

🧠 Conceptual

expert

What happens if MSET is interrupted mid-operation?

Consider a Redis server crash occurring during an MSET command that sets multiple keys.

Which statement best describes the state of the keys after the server restarts?

A Either all keys are set or none are set, due to atomicity of MSET.

B Some keys may be set while others remain unchanged, partial update possible.

C Redis rolls back all changes automatically on crash.

D All keys are set but with empty string values.

💡 Hint

Think about atomicity guarantees of MSET in Redis.

MSET is atomic in Redis, so either all keys are set or none are set, even if interrupted.