LISTEN/NOTIFY ultra slow speed

    Hello! I'm having trouble with LISTEN/NOTIFY speed. Now I have about 100-200 (few?) clients who are actively messaging. But recently I started to notice a drop in speed. Changing the log_min_duration_statement parameter did not show slow queries in the log.

    As it turned out, the pg_notify(text ,text) function

          or the

          NOTIFY text, 'text' queries takes an extremely long time (0.7-1.5sec),

    but the select pg_notification_queue_usage() query always returns 0.

Please tell me what's the matter, where did I make a mistake? 

What needs to be done to increase the speed of adding to the message queue?