PUBSUB command is useful to view the state of the Pub/Sub system in Yugabyte. These commands only provide information regarding the specific YEDIS
server that is queried. 3 subcommands are supported:
PUBSUB channels [pattern]
Lists the currently active channels (optionally matching the given pattern) on the YEDIS server that is queried -- i.e. channels with one or more
subscribers on the node that the client is connected to.
PUBSUB NUBSUB [channel-1 .. channel-n]
Returns the number of subscribers for the specified channels (not counting the clients that are subscribed to patterns) on the YEDIS server that is queried.
Returns the number of patterns that are subscribed to on the YEDIS server that is queried.