record_min_max=False exports histogram min=+Infinity and max=-Infinity

Describe your environment

Labels: bug, sdk, metrics, exporter
Affected packages: opentelemetry-sdk
Found on: main @ 0a5d76b6
Environment: CPython 3.12

What happened?

Both histogram aggregations seed _min/_max with math.inf and -math.inf and never consult self._record_min_max in collect(). With min/max recording disabled the sentinels are handed straight to the data point, and the OTLP encoder sets both optional fields as present - so a backend receives a histogram whose minimum is +Infinity and maximum is -Infinity.

to_json has the same problem and emits the bare literals Infinity and -Infinity, which are not valid JSON.

Steps to Reproduce

from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.metrics.export import InMemoryMetricReader
from opentelemetry.sdk.metrics.view import ExplicitBucketHistogramAggregation, View

reader = InMemoryMetricReader()
provider = MeterProvider(
    metric_readers=[reader],
    views=[View(instrument_name="hist",
                aggregation=ExplicitBucketHistogramAggregation(record_min_max=False))],
)
histogram = provider.get_meter("m").create_histogram("hist")
histogram.record(5)
histogram.record(50)

point = reader.get_metrics_data().resource_metrics[0].scope_metrics[0].metrics[0].data.data_points[0]
print(point.min, point.max)
print(point.to_json())

Expected Result

min and max are absent from the data point and from the encoded OTLP message, since OTLP declares them optional double.

Actual Result

--- ExplicitBucketHistogram(record_min_max=False) ---
  SDK data point : min=inf  max=-inf  sum=55  count=2
  OTLP protobuf  : HasField(min)=True min=inf   HasField(max)=True max=-inf
--- ExponentialBucketHistogram(record_min_max=False) ---
  OTLP protobuf  : HasField(min)=True min=inf   HasField(max)=True max=-inf

# to_json, parsed by a strict RFC 8259 reader
to_json() emits: "min": Infinity, "max": -Infinity
strict JSON parse: non-JSON constant 'Infinity'

# and the data-model invariant is violated outright
min=inf  max=-inf  ->  min > max

Additional context

Corrupt histogram data for anyone who disables min/max recording - a reasonable thing to do, since it is exactly the knob you reach for to cut per-series cost. A backend charting minimum latency reads +Infinity; anything computing max - min gets nonsense; and the min > max invariant that consumers are entitled to rely on is violated.

Separately, to_json produces output that a conformant JSON parser rejects, which affects ConsoleMetricExporter and anything else built on the SDK's own serialisation.

Would you like to implement a fix?

Yes

Tip

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Start with ExplicitBucketHistogramAggregation and ExponentialBucketHistogram, then trace collect(), the OTLP encoding path, and to_json(). Reproduce the case with InMemoryMetricReader and record_min_max=False. Done means min and max are absent when disabled, the OTLP optional fields are unset, and to_json() is accepted by a strict JSON parser.