Explain Periodic_flush in logsatsh common fields

Hi,

Under Logstash common fields, I see a field names Periodic_flush. Could you please explain whats is used for and also give an example with respect to translate plugin

https://www.elastic.co/guide/en/logstash/current/plugins-filters-translate.html#plugins-filters-translate-periodic_flush

https://www.elastic.co/guide/en/logstash/current/plugins-filters-http.html#plugins-filters-http-periodic_flush

periodic_flush is a configuration item that filters inherit from the base filter class. For a translate filter it has no use. For an aggregate filter it is used to trigger the flushing of events based on timeouts. Whenever the flush method is called (every 3 seconds?) the filter checks to see if any items in the map have expired.