52. Naming spans

Picking a span name is not a trivial task. Span name should depict an operation name. The name should be low cardinality (e.g. not include identifiers).

Since there is a lot of instrumentation going on some of the span names will be artificial like:

• controller-method-name when received by a Controller with a method name conrollerMethodName

• async for asynchronous operations done via wrapped Callable and Runnable .

• @Scheduled annotated methods will return the simple name of the class.

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

52.1 @SpanName annotation

You can name the span explicitly via the @SpanName annotation.

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

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

In this case, when processed in the following manner:

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

The span will be named calculateTax .

52.2 toString() method

It’s pretty rare to create separate classes for Runnable or Callable . Typically one creates an anonymous instance of those classes. You can’t annotate such classes thus to override that, if there is no @SpanName annotation present, we’re checking if the class has a custom implementation of the toString() method.

So executing such code:

Runnable runnable = new TraceRunnable(tracer, 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();

will lead in creating a span named calculateTax .