57. Naming spans

Picking a span name is not a trivial task. A span name should depict an operation name. The name should be low cardinality, so it should not include identifiers.

Since there is a lot of instrumentation going on, some span names are artificial:

• controller-method-name when received by a Controller with a method name of controllerMethodName

• async for asynchronous operations done with wrapped Callable and Runnable interfaces.

• Methods annotated with @Scheduled return the simple name of the class.

Fortunately, for asynchronous processing, you can provide explicit naming.

57.1 @SpanName Annotation

You can name the span explicitly by using the @SpanName annotation, as shown in the following example:

@SpanName("calculateTax")
class TaxCountingRunnable implements Runnable {

	@Override public void run() {
		// perform logic
	}
}

In this case, when processed in the following manner, the span is named calculateTax :

Runnable runnable = new TraceRunnable(tracing, spanNamer,
		new TaxCountingRunnable());
Future<?> future = executorService.submit(runnable);
// ... some additional logic ...
future.get();

57.2 toString() method

It is pretty rare to create separate classes for Runnable or Callable . Typically, one creates an anonymous instance of those classes. You cannot annotate such classes. To overcome that limitation, if there is no @SpanName annotation present, we check whether the class has a custom implementation of the toString() method.

Running such code leads to creating a span named calculateTax , as shown in the following example:

Runnable runnable = new TraceRunnable(tracing, spanNamer, new Runnable() {
	@Override public void run() {
		// perform logic
	}

	@Override public String toString() {
		return "calculateTax";
	}
});
Future<?> future = executorService.submit(runnable);
// ... some additional logic ...
future.get();