One row per hop, and the id that links them — parent span ids and read-time assembly

1def start_span(name, ctx, kind = INTERNAL):
2    span = Span()
3    span.name = name          # the only required argument
4    span.start_time = now()
5    parent = ctx.current_span
6    span.trace_id = parent.trace_id if parent else new_id()
7    span.span_id = new_span_id()
8    span.parent_span_id = parent.span_id if parent else ""
9    span.kind = kind          # SERVER, CLIENT, PRODUCER, …
10    span.status = UNSET       # Ok is asserted, not inferred
11    return span

1def end(span):
2    span.end_time = now()
3    span.duration = span.end_time - span.start_time
4    # nothing is nested here: no child is attached,
5    # no parent is notified, no sibling is waited for
6    exporter.enqueue(span)
7 
8def on_batch(batch):            # BatchSpanProcessor
9    for span in batch:
10        collector.send(span)    # each record travels alone

1def build_tree(trace_id):
2    rows = store.scan(trace_id = trace_id)
3    children = defaultdict(list)
4    root = None
5    for row in rows:
6        if row.parent_span_id == "":   # empty => root
7            root = row
8        else:
9            children[row.parent_span_id].append(row)
10    # no timestamp, host or arrival index is ever read here
11    # a parent id naming a row that is absent matches nothing
12    return render(root, children)