All the spans of one request share a blank. Each span has its own blank and records its blank's, which is how the tracing system rebuilds the call tree.

Answer

All the spans of one request share a trace id. Each span has its own span id and records its parent's, which is how the tracing system rebuilds the call tree.

Also accepted: trace ID for trace id; span ID for span id; parent span for parent.

Why

A span covers one unit of work (an HTTP call, a query) with its start, duration and attributes. Laid out as a tree on a timeline, the spans show where the time went and which calls ran in sequence that could run in parallel.

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