Redis keyspace notifications with StackExchange.Re

Question

I've looking around and I'm unable to find how to perform a subscription to keyspace notifications on Redis using StackExchange.Redis library.

Checking available tests I've found pubsub using channels, but this is more to work like a service bus/queueing rather than subscribing to specific Redis key events.

Is it possible to take advantage of this Redis feature using StackExchange.Redis?

Answer 1

Just to extend what the selected answer already describes:

using (ConnectionMultiplexer connection = ConnectionMultiplexer.Connect("localhost"))
{
    IDatabase db = connection.GetDatabase();
    ISubscriber subscriber = connection.GetSubscriber();

    subscriber.Subscribe($"__keyspace@0__:{channel}", (channel, value) =>
        {
          // Do whatever channel specific handling you need to do here, in my case I used exact Key name that I wanted expiration event for.  
        }
    );
}

Another important thing, I had to subscribe KEx (CONFIG SET notify-keyspace-events KEx ) to get channel based updates for expiration notifications.

Answer 2

The regular subscriber API should work fine - there is no assumption on use-cases, and this should work fine.

However, I do kinda agree that this is inbuilt functionality that could perhaps benefit from helper methods on the API, and perhaps a different delegate signature - to encapsulate the syntax of the keyapace notifications so that people don't need to duplicate it. For that: I suggest you log an issue so that it doesn't get forgotten.

Simple sample of how to subscribe to a keyspace event

First of all, it's important to check that Redis keyspace events are enabled. For example, events should be enabled on keys of type Set. This can be done using CONFIG SET command:

CONFIG SET notify-keyspace-events KEs

Once keyspace events are enabled, it's just about subscribing to the pub-sub channel:

using (ConnectionMultiplexer connection = ConnectionMultiplexer.Connect("localhost"))
{
    IDatabase db = connection.GetDatabase();
    ISubscriber subscriber = connection.GetSubscriber();

    subscriber.Subscribe("__keyspace@0__:*", (channel, value) =>
        {
            if ((string)channel == "__keyspace@0__:users" && (string)value == "sadd")
            {
                // Do stuff if some item is added to a hypothethical "users" set in Redis
            }
        }
    );
}

Learn more about keyspace events here.