This stream function emits a row at a regular interval.
SYS_BOOT.UTIL.PING(intervalMillisecs)
select stream rowtime,* from stream(PING(2000));
'ROWTIME','PING'
'2021-04-12 08:00:23.918','Ping'
'2021-04-12 08:00:25.918','Ping'
'2021-04-12 08:00:27.918','Ping'
'2021-04-12 08:00:29.918','Ping'
'2021-04-12 08:00:31.918','Ping'
'2021-04-12 08:00:33.918','Ping'
'2021-04-12 08:00:35.918','Ping'
This stream can be joined with data streams to help to identify (for example) periods where no data is received.
NOTE: In the example above, the pings do not appear on rounded 2 second boundaries from 08:00:24.000 - they appear immediately at 08:00:23.918 (the time the SELECT started) and every 2 seconds from then.