UNLINK

Introduction and Use Case(s)

The UNLINK command in Redis is used to delete one or more keys. Unlike the traditional DEL command, UNLINK is non-blocking: it runs in constant time by delegating the actual removal of the keys to a background thread. This makes it particularly useful in scenarios where you need to delete large datasets without impacting the performance of your Redis server.

Syntax

UNLINK key [key ...]

Parameter Explanations

• key: The name of the key to be removed. You can specify multiple keys in a single UNLINK command. If a key does not exist, it is ignored.

Return Values

The UNLINK command returns an integer representing the number of keys that were successfully unlinked.

Example Outputs

• (integer) 1 — One key was successfully unlinked.
• (integer) 0 — No keys were unlinked, possibly because they did not exist.

Code Examples

dragonfly> SET mykey "value"
OK
dragonfly> UNLINK mykey
(integer) 1
dragonfly> EXISTS mykey
(integer) 0
dragonfly> SET key1 "value1"
OK
dragonfly> SET key2 "value2"
OK
dragonfly> UNLINK key1 key2 key3
(integer) 2

Best Practices

• Use UNLINK instead of DEL for deleting large keys or multiple keys to avoid blocking the Redis event loop.
• Regularly monitor and clean up keys that are no longer needed to optimize memory usage.

Common Mistakes

• Attempting to UNLINK keys that do not exist will not generate an error but will count as non-unlinked keys in the return value.
• Misunderstanding that UNLINK immediately frees memory. The memory cleanup happens asynchronously, which can lead to temporary memory spikes if large datasets are unlinked frequently.

FAQs

What is the difference between DEL and UNLINK?

DEL is a blocking command that deletes keys in a synchronous manner, whereas UNLINK is non-blocking and delegates the deletion process to a background thread for faster performance.

Can UNLINK be used with any type of key?

Yes, UNLINK can be used with any type of key including strings, lists, sets, hashes, and more.