链路采样减少数据量，但不会固定成本上限

import json
from collections import Counter

from opentelemetry.context import Context
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import SimpleSpanProcessor
from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
from opentelemetry.sdk.trace.id_generator import IdGenerator
from opentelemetry.sdk.trace.sampling import ParentBased, TraceIdRatioBased
from opentelemetry.trace import Status, StatusCode
from opentelemetry.trace.propagation.tracecontext import TraceContextTextMapPropagator


class TestIds(IdGenerator):
    # Controlled test inputs only; production IDs need suitable randomness.
    def __init__(self):
        self.trace_index = 0
        self.span_index = 0

    def generate_trace_id(self):
        index = self.trace_index
        self.trace_index += 1
        return ((index + 1) << 64) | (index * (1 << 60) + 1)

    def generate_span_id(self):
        self.span_index += 1
        return self.span_index


exporter = InMemorySpanExporter()
provider = TracerProvider(sampler=ParentBased(TraceIdRatioBased(0.5)),
                          id_generator=TestIds())
provider.add_span_processor(SimpleSpanProcessor(exporter))
tracer = provider.get_tracer("sampling-lab")
executed_children = 0
late_error_recording = None
for index in range(16):
    with tracer.start_as_current_span(f"root-{index}", context=Context()) as root:
        for child in range(2):
            with tracer.start_as_current_span(f"child-{index}-{child}"):
                executed_children += 1
        if index == 15:
            late_error_recording = root.is_recording()
            root.set_status(Status(StatusCode.ERROR, "error discovered after start"))
assert provider.force_flush()
spans = exporter.get_finished_spans()
counts = Counter(span.context.trace_id for span in spans)
assert len(counts) == 8 and set(counts.values()) == {3} and len(spans) == 24
assert {s.name for s in spans if s.parent is None} == {f"root-{i}" for i in range(8)}
assert executed_children == 32 and late_error_recording is False
assert not any(span.name == "root-15" for span in spans)

exporter.clear()
propagator = TraceContextTextMapPropagator()
for flag, label in (("01", "sampled"), ("00", "unsampled")):
    # High trace-ID bits do not override an accepted remote parent's flag.
    header = f"00-1111111111111111ffffffffffffffff-2222222222222222-{flag}"
    context = propagator.extract({"traceparent": header}, context=Context())
    with tracer.start_as_current_span(label, context=context):
        with tracer.start_as_current_span(label + "-child"):
            pass
assert provider.force_flush()
remote_spans = exporter.get_finished_spans()
assert {span.name for span in remote_spans} == {"sampled", "sampled-child"}
assert next(span for span in remote_spans if span.name == "sampled").parent.is_remote
print(json.dumps({"controlled_roots": 16, "exported_traces": len(counts),
                  "exported_spans": len(spans), "executed_child_operations": executed_children,
                  "late_error_was_recording": late_error_recording,
                  "remote_parent_exported_spans": len(remote_spans)}, indent=2))
provider.shutdown()