INCRBY and DECRBY in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of INCRBY on a key with an integer value?

Given a Redis key counter with value 10, what will be the value of counter after running INCRBY counter 5?

Redis

SET counter 10
INCRBY counter 5
GET counter

A 15

B 5

C 10

D Error: value is not an integer

💡 Hint

INCRBY adds the given number to the current integer value stored at the key.

The INCRBY command increases the integer value stored at the key by the specified amount. Since the initial value is 10, adding 5 results in 15.

❓ query_result

intermediate

What happens when DECRBY is used on a non-existing key?

What will be the value of key score after running DECRBY score 3 if score does not exist before?

Redis

DEL score
DECRBY score 3
GET score

A 3

B 0

C -3

D Error: key does not exist

💡 Hint

Redis treats non-existing keys as 0 for increment/decrement commands.

If the key does not exist, Redis treats its value as 0. Then DECRBY score 3 subtracts 3, resulting in -3.

📝 Syntax

advanced

Which command syntax is correct for incrementing a key by 10?

Choose the correct Redis command to increase the value of key visits by 10.

A INCRBY visits 10

B INCR visits 10

C INCRBY 10 visits

D INCRBY(visits, 10)

💡 Hint

The syntax is INCRBY key increment.

The correct syntax for incrementing a key by a specific number is INCRBY key increment. Options B, C, and D are invalid syntax.

❓ query_result

advanced

What error occurs when INCRBY is used on a key holding a string?

If key name holds the string value "Alice", what happens when running INCRBY name 1?

Redis

SET name "Alice"
INCRBY name 1

A Value becomes 0

B Value becomes "Alice1"

C Value becomes 1

D Error: value is not an integer or out of range

💡 Hint

INCRBY only works on keys holding integer values.

Redis throws an error if you try to increment a key holding a non-integer string value.

🧠 Conceptual

expert

How does Redis handle concurrent INCRBY and DECRBY commands on the same key?

Consider multiple clients running INCRBY counter 2 and DECRBY counter 1 concurrently on the same key counter. What guarantees does Redis provide about the final value?

A Redis queues commands but applies only increments or only decrements, ignoring the other.

B Redis guarantees atomicity; all increments and decrements are applied without race conditions, so the final value is consistent.

C Redis may lose some increments or decrements due to race conditions, so the final value is unpredictable.

D Redis locks the key permanently after the first command, blocking others indefinitely.

💡 Hint

Redis commands like INCRBY and DECRBY are atomic operations.

Redis processes commands sequentially and atomically, so concurrent INCRBY and DECRBY commands on the same key do not cause race conditions. The final value reflects all operations applied in some order.