DEL and UNLINK for deletion in Redis - Step-by-Step Execution

Concept Flow - DEL and UNLINK for deletion

Start

↓

Receive DEL or UNLINK command

↓

Check if key exists

Yes No↓

DEL: Remove key synchronously

↓

UNLINK: Remove key asynchronously

↓

Return number of keys deleted

↓

End

The flow shows how Redis processes DEL and UNLINK commands: it checks if the key exists, then deletes it either synchronously (DEL) or asynchronously (UNLINK), and returns the count of deleted keys.

Execution Sample

Redis

DEL mykey
UNLINK mykey

Illustrates deletion of key 'mykey' using DEL (synchronous) and UNLINK (asynchronous).

Execution Table

Step	Command	Key Exists?	Action	Result	Notes
1	DEL mykey	Yes	Remove key synchronously	1	Key 'mykey' deleted immediately
2	DEL mykey	No	No action	0	Key 'mykey' does not exist
3	UNLINK mykey	Yes	Schedule key removal asynchronously	1	Key 'mykey' marked for async deletion
4	UNLINK mykey	No	No action	0	Key 'mykey' does not exist

💡 Execution stops after command returns number of keys deleted or 0 if key not found

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
mykey existence	Varies	Does not exist	Does not exist	Deleted (async removal scheduled)	Does not exist

Key Moments - 2 Insights

Why does DEL delete the key immediately but UNLINK does not?

DEL removes the key synchronously during the command execution (see Step 1), while UNLINK schedules the key for asynchronous deletion to avoid blocking Redis (see Step 3).

What happens if the key does not exist when DEL or UNLINK is called?

Both commands return 0 and do nothing if the key does not exist (see Steps 2 and 4 in the execution table).

Visual Quiz - 3 Questions

Look at the execution table, what is the result of DEL when the key exists?

A 1

B 0

C Error

D Key remains

💡 Hint

Check Step 1 in the execution_table under the Result column

At which step does UNLINK schedule the key for asynchronous deletion?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the Action column for UNLINK commands in the execution_table

If the key does not exist, what do both DEL and UNLINK return?

A 1

B 0

C Error

D Null

💡 Hint

See Steps 2 and 4 in the execution_table Result column

Concept Snapshot

DEL and UNLINK remove keys in Redis.
DEL deletes keys immediately and blocks until done.
UNLINK schedules keys for asynchronous deletion to avoid blocking.
Both return the number of keys deleted (0 if none).
Use DEL for immediate removal, UNLINK for non-blocking deletion.

Full Transcript

This visual execution shows how Redis handles the DEL and UNLINK commands for deleting keys. When a command is received, Redis checks if the key exists. If it does, DEL removes the key immediately and returns 1, indicating one key deleted. UNLINK, on the other hand, schedules the key for asynchronous deletion to avoid blocking Redis, also returning 1. If the key does not exist, both commands return 0 and do nothing. The variable tracker shows the key's existence changing from present to deleted after DEL, and marked for async removal after UNLINK. Key moments clarify why DEL blocks and UNLINK does not, and what happens when keys are missing. The quiz tests understanding of these steps and results.