Detect

Finds sequences of events that match a pattern within a maximum duration.

Detect runs an automaton (Trill’s AFA) over the stream. SingleElement(predicate) steps match one event each, in order. A match is reported when its last event arrives, and it lives until the first event of the match plus maxDuration.

In the diagram the pattern is “an a, then a b, within 4”. a at 1 and b at 2 give a match [2,5): it starts at 2, when the b completes it, and ends at 1 + 4. a at 4 and b at 7 give [7,8), ending at 4 + 4. The a at 9 has no b after it.

Drag the b at 7 to 9 and the second match disappears: a match starting with the a at 4 must complete before 4 + 4. Drag it to 10, 11 or 12 and a new match forms instead, with the a at 9. From 13 on, that match has expired too, and only the first match remains.

See also: AlterEventDuration, Join