Ignore reader preferred aggregations incompatible with async instruments

[Eason09053360]

No existing issue — found by reading the code.

MetricReaderStorage warns and skips a View that configures a histogram
aggregation for an asynchronous instrument. The same aggregation set through
MetricReader(preferred_aggregation=...) skips that check and silently produces
no data at all: histogram aggregations only implement the DELTA instrument
temporality path, so asynchronous instruments (always CUMULATIVE) return None
from every collect().

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

reader = InMemoryMetricReader(
    preferred_aggregation={ObservableCounter: ExplicitBucketHistogramAggregation()}
)
meter = MeterProvider(metric_readers=[reader]).get_meter("repro")
meter.create_observable_counter("my_counter", callbacks=[lambda options: [Observation(7)]])

print(reader.get_metrics_data())  # None, and nothing logged

Both histogram aggregations and all three asynchronous instrument classes are
affected. Synchronous instruments are not, so the OTLP exporter's
OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION handling (which maps
Histogram) is unchanged.

This warns and keeps the instrument's default aggregation, matching what the
View path already does.

Related: #5461 fixes the matching gap on the View path. Different file and
function, so the two can be reviewed independently.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• New test_configure_aggregation_asynchronous_histogram_incompatibility
  (3 async instrument classes × both histogram aggregations) and
  test_configure_aggregation_synchronous_histogram_allowed.
• opentelemetry-sdk/tests/metrics/ — 309 passed, 1 skipped.

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

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Waiting on reviewers · refreshed 2026-08-21 01:46 UTC

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