Comment by cryptonector

One can replace LISTEN/NOTIFY with logical replication / CDC. And it's funny because somehow, somewhere, PG must be serializing the writing of the WAL to some degree. So it's not clear to me why LISTEN/NOTIFY needs additional serialization. Perhaps PG should turn NOTIFY into INSERTs on a special table that a worker process watches and turns those inserts into notifies (and deletes the inserts).