To use Latency, the Latency Feature must be installed.
Latency describes the time how long it takes for an event from entering the system until it triggers a result. In Odysseus, latency time stamps are added to each event (if latency mode is activated). This is the system time in nano seconds, when the event is received. As long as only one event is involved in the creation of a result, the latency is not manipulated. If the result is the combination of dierent events (as for the aggregation or for the join), the latency is typically dened as the latency of the last participating event. This is because the waiting time of an event for its corresponding event in another stream depends not on the processing capability of the system but the data distribution. Although, for some applications it might be interesting how long the oldest participating event is been processed. For this issue, Odysseus keeps both values as meta data.
In Odysseus, a special CALCLATENCY operator is needed to get the real latency values where ever the current latency should be calculated. For most queries, this should always done before the last operation (e.g., before writing the result to sinks).