CREATE EXTENSION pg_statviz;
SELECT 1 FROM pgstatviz.snapshot();
NOTICE:  created pg_statviz snapshot
 ?column? 
----------
        1
(1 row)

SELECT count(*)
    FROM pgstatviz.conn t
    JOIN pgstatviz.snapshots s USING (snapshot_tstamp);
 count 
-------
     1
(1 row)