INCRBY and DECRBY in Redis - Step-by-Step Execution

Concept Flow - INCRBY and DECRBY

Start with a key holding a number

↓

Receive INCRBY or DECRBY command

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Add or subtract the given amount

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Update the key with new value

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Return the new value

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End

The flow shows how Redis takes a key with a number, changes it by adding or subtracting a specified amount, updates the key, and returns the new value.

Execution Sample

Redis

SET counter 10
INCRBY counter 5
DECRBY counter 3

This sequence sets a counter to 10, increases it by 5, then decreases it by 3.

Execution Table

Step	Command	Key Value Before	Operation	Key Value After	Returned Value
1	SET counter 10	N/A	Set to 10	10	OK
2	INCRBY counter 5	10	10 + 5	15	15
3	DECRBY counter 3	15	15 - 3	12	12
4	END	12	No more commands	12	N/A

💡 No more commands to execute; final value of 'counter' is 12.

Variable Tracker

Variable	Start	After 1	After 2	Final
counter	N/A	10	15	12

Key Moments - 2 Insights

Why does INCRBY return the new value instead of the old one?

INCRBY returns the updated value after adding the increment, as shown in step 2 of the execution_table where the returned value is 15, reflecting the new state.

What happens if the key does not exist before INCRBY or DECRBY?

If the key does not exist, Redis treats it as 0 before applying INCRBY or DECRBY, so the operation still works and sets the key to the increment or decrement value.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'counter' after step 2?

A 15

B 10

C 12

D 5

💡 Hint

Check the 'Key Value After' column in row for step 2.

At which step does the 'counter' value become 12?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Key Value After' column and find when it changes to 12.

If we changed INCRBY counter 5 to INCRBY counter 2, what would be the new value after step 2?

A 17

B 12

C 10

D 7

💡 Hint

Add 2 to the initial value 10 as shown in the variable_tracker.

Concept Snapshot

INCRBY key increment
DECRBY key decrement

Both commands change the integer value stored at key by adding or subtracting the given number.
If key does not exist, it is treated as 0.
They return the new value after the operation.

Full Transcript

This visual execution shows how Redis commands INCRBY and DECRBY work. We start with a key 'counter' set to 10. Then INCRBY adds 5, making it 15, and DECRBY subtracts 3, making it 12. Each step updates the key and returns the new value. If the key did not exist, Redis would treat it as zero before changing it. This helps understand how these commands modify numeric values stored in Redis keys.