// Module included in the following assemblies:
//
// assembly-distributed tracing.adoc

[id='ref-tracing-span-names-{context}']
= Custom span names

[role="_abstract"]
A tracing __span__ is a logical unit of work in Jaeger, with an operation name, start time, and duration. 
Spans have built-in names, but you can specify custom span names in your Kafka client instrumentation where used. 

Specifying custom span names is optional and only applies when using a decorator pattern xref:proc-instrumenting-producers-consumers-for-opentracing-{context}[in producer and consumer client instrumentation] or xref:proc-instrumenting-kafka-streams-with-tracers-{context}[Kafka Streams instrumentation]. 

== Specifying span names for OpenTelemetry

Custom span names cannot be specified directly with OpenTelemetry.
Instead, you retrieve span names by adding code to your client application to extract additional tags and attributes.

.Example code to extract attributes
[source,java,subs=attributes+]
----
//Defines attribute extraction for a producer
private static class ProducerAttribExtractor implements AttributesExtractor < ProducerRecord < ? , ? > , Void > {
    @Override
    public void onStart(AttributesBuilder attributes, ProducerRecord < ? , ? > producerRecord) {
        set(attributes, AttributeKey.stringKey("prod_start"), "prod1");
    }
    @Override
    public void onEnd(AttributesBuilder attributes, ProducerRecord < ? , ? > producerRecord, @Nullable Void unused, @Nullable Throwable error) {
        set(attributes, AttributeKey.stringKey("prod_end"), "prod2");
    }
}
//Defines attribute extraction for a consumer
private static class ConsumerAttribExtractor implements AttributesExtractor < ConsumerRecord < ? , ? > , Void > {
    @Override
    public void onStart(AttributesBuilder attributes, ConsumerRecord < ? , ? > producerRecord) {
        set(attributes, AttributeKey.stringKey("con_start"), "con1");
    }
    @Override
    public void onEnd(AttributesBuilder attributes, ConsumerRecord < ? , ? > producerRecord, @Nullable Void unused, @Nullable Throwable error) {
        set(attributes, AttributeKey.stringKey("con_end"), "con2");
    }
}
//Extracts the attributes
public static void main(String[] args) throws Exception {
        Map < String, Object > configs = new HashMap < > (Collections.singletonMap(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092"));
        System.setProperty("otel.traces.exporter", "jaeger");
        System.setProperty("otel.service.name", "myapp1");
        KafkaTracing tracing = KafkaTracing.newBuilder(GlobalOpenTelemetry.get())
            .addProducerAttributesExtractors(new ProducerAttribExtractor())
            .addConsumerAttributesExtractors(new ConsumerAttribExtractor())
            .build();
----

== Specifying span names for OpenTracing

To specify custom span names for OpenTracing, pass a `BiFunction` object as an additional argument when instrumenting producers and consumers.

For more information on built-in names and specifying custom span names to instrument client application code in a decorator pattern, see the {OpenTracingKafkaClientDocs}.