Using the Metronome Operator

The Metronome delivers output tuples periodically based on the system clock, at an interval that you specify. In the same way that a musician's metronome can be used to indicate the exact tempo of a piece of music, you can use the StreamBase Metronome operator to control the timing of downstream operations by a connected component.

For example, the following EventFlow shows a Metronome being used to emit a timer tuple every five seconds. In effect, the read operation of the connected Query operator will occur at that interval. The read operation is a lookup of the current share Price from the NameValuePairs Query Table:

A Metronome operator does not receive any input tuples, has zero input ports, and therefore does not pay attention to timestamp fields. Each Metronome operator has one output port. Unlike the related Heartbeat operator, the Metronome operator does not provide a slack property, which means there is no variance in the emit interval for each timer tuple.

You can specify a parameter in the form ${parameter} for the Tuple output interval property.

You might use a Metronome operator to activate one flow in your StreamBase application on a periodic basis, because a consumer of an output stream is unable to keep up with the speed that data enters into, and is processed by, StreamBase.

A StreamBase application can have one or more Metronome operators, each with different timing values. You can also have a StreamBase application that uses one or more Metronome operators plus one or more Heartbeat operators. Think of a StreamBase Heartbeat operator as another type of timing mechanism. Unlike the Metronome operator, a Heartbeat operator's pulse can vary (like a person's beating heart, which can speed up or slow down). You can specify the amount of variance or slack that is allowed by the Heartbeat operator.

Name: Use this field to specify or change the component's name, which must be unique in the application. The name must contain only alphabetic characters, numbers, and underscores, and no hyphens or other special characters. The first character must be alphabetic or an underscore.

Enable Error Output Port: Select this check box to add an Error Port to this component. In the EventFlow canvas, the Error Port shows as a red output port, always the last port for the component. See Using Error Ports and Error Streams to learn about Error Ports.

Description: Optionally enter text to briefly describe the component's purpose and function. In the EventFlow canvas, you can see the description by pressing Ctrl while the component's tooltip is displayed.

The Output Settings tab allows you to specify:

Use the Concurrency tab to specify separate threading for this instance of this component. The own thread check box is a candidate for selection if this component instance is long-running or compute-intensive, can run without data dependencies on other StreamBase components, and would not cause the containing module to block while waiting for a thread to return. In this case, you may be able to improve performance by selecting this option. This option causes StreamBase Server to process this component concurrently with other processing in the application. The operating systems supported by StreamBase automatically distribute the processing of threads across multiple processors.

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