As a rule, you should listen for only those events or streams that you are interested in now. Apama applications typically define monitors that spawn to handle a new situation, for example, to automatically manage the trading of a new large order. Each monitor instance is usually interested in only one particular substream of a larger stream, for example, Tick events for a particular stock rather than all Tick events.

Consequently, the common pattern is to create a new monitor instance and for that instance to set up stream queries that process the events of interest, for example, to calculate the average price. This is more efficient than defining a monitor that processes all events (for example, all Tick events for all stocks), generates added-value items and then forwards these items to client monitors. However, there are situations when the latter approach is required. You should decide which solution approach is best in which circumstances.