Using UNLINK instead of DEL in the MIGRATE command

[afshinsa]

As you might know Redis already provides config knobs to replace DEL with UNLINK in different situations like eviction, expiration and user delete.

Key migration (MIGRATE) is also using DEL internally to delete a key after copying it to the destination node:

"The command internally uses DUMP to generate the serialized version of the key value, and RESTORE in order to synthesize the key in the target instance. The source instance acts as a client for the target instance. If the target instance returns OK to the RESTORE command, the source instance deletes the key using DEL."

My question for the community is that if you see any downsides in replacing DEL with UNLINK in the key migration function. In other words, is there a reason that there is no config knob for this particular DEL use case.

I want to convert only DEL command issued by MIGRATE to UNLINK, not all DEL commands.

[stockholmux]

Since Valkey 8.0. the default config for lazyfree-lazy-user-del is 'yes' meaning that any an DEL is run as UNLINK under the hood across the board.

There is very little value in ever using a synchronous DEL in Valkey, so the knob isn't really needed beyond 'yes'/'no'

[afshinsa]

This is very helpful to know, but in this specific case the DEL is Valkey internal i.e. issued by the MIGRATE command so it won't be covered by lazyfree-lazy-user-del.