spanId property

The ID of the Cloud Trace (https://cloud.google.com/trace) span associated with the current operation in which the log is being written.

For example, if a span has the REST resource name of "projects/some-project/traces/some-trace/spans/some-span-id", then the span_id field is "some-span-id".A Span (https://cloud.google.com/trace/docs/reference/v2/rest/v2/projects.traces/batchWrite#Span) represents a single operation within a trace. Whereas a trace may involve multiple different microservices running on multiple different machines, a span generally corresponds to a single logical operation being performed in a single instance of a microservice on one specific machine. Spans are the nodes within the tree that is a trace.Applications that are instrumented for tracing (https://cloud.google.com/trace/docs/setup) will generally assign a new, unique span ID on each incoming request. It is also common to create and record additional spans corresponding to internal processing elements as well as issuing requests to dependencies.The span ID is expected to be a 16-character, hexadecimal encoding of an 8-byte array and should not be zero. It should be unique within the trace and should, ideally, be generated in a manner that is uniformly random.Example values: 000000000000004a 7a2190356c3fc94b 0000f00300090021 d39223e101960076

Optional.