Support keyspace notifications

[Cylkal]

Redis support keyspace notifications by command CONFIG SET notify-keyspace-events xE, but dragonfly does not support it:

CONFIG SET notify-keyspace-events xE
(error) ERR CONFIG SET failed (possibly related to argument 'notify-keyspace-events').

I'd like to subscribe to timeout key events. Is there any solution?

[romange]

Dragonfly does not support key events. Specifically, timeout events is not designed well in Redis and does not guarantee accurate events for all the keys. Can you please describe your use-case for this ?

[Cylkal]

@romange My scenario is to monitor which key expires in real time, which was previously achieved by subscribing to redis's key expiration event. In my system, key expiration means that the tasks corresponding to this key may not be handled in a timely manner, and a mechanism is needed to monitor these tasks that are not handled in time. It is true that the redis key event is not a reliable method, but it does not need to implement too many functions alone, so it is convenient.

[glad2os]

@romange My scenario is to monitor which key expires in real time, which was previously achieved by subscribing to redis's key expiration event. In my system, key expiration means that the tasks corresponding to this key may not be handled in a timely manner, and a mechanism is needed to monitor these tasks that are not handled in time. It is true that the redis key event is not a reliable method, but it does not need to implement too many functions alone, so it is convenient.

Are there other methods besides the one you mentioned? Because I'm using the same thing in my project

[ostlerc]

We cannot convert redis to dragonflydb in some scenarios due to this limitation. Happy to answer any other questions about this use case. But it does seem like a necessary feature of redis to support.

[Guillermogsjc]

Hi @romange,

The lack of support for key space notification events is a blocker in some cases, such as real-time applications where a WebSocket endpoint receives Pub/Sub messages triggered by key changes to send updated key data to clients, among other use cases.

As you mentioned, timeout events pose challenges for porting this functionality, which has hindered the development of this feature.

My question is: Could the part of the API that supports other key operations—such as hset, hdel, del, set, etc.—be developed for DragonflyDB, as these would be very useful? (e.g. develop partially and support only the events that fit nicely into DragonflyDB so far)

[romange]

https://github.com/dragonflydb/dragonfly/pull/3154/files fixes the specific usecase, i.e. Ex notifications.

Please open a separate issue for notification use-cases that are not covered by Ex.