Histogram.record() producing inaccurate start_time_unix_nano value

[williamdoddsb365]

Describe your environment

OS: CentOS 7
Python version: Python3.11
SDK version: 1.26.0
API version: 1.26.0

What happened?

When using Python OpenTelemetry (OTel) to record histogram metrics with unique integer attributes, all recorded histograms are showing a static start_time_unix_nano value in the OpenTelemetry logs. Despite different timestamps being recorded for each metric point, the start_time_unix_nano remains constant across all data points, which is not expected behavior. This issue does not occur when static attribute values are used.

Steps to Reproduce

There is an easy to follow MRE here:
https://github.com/williamdoddsb365/otel_histogram_issue

Expected Result

The start_time_unix_nano value should increment for each recorded histogram data point, regardless of whether the attributes are static or dynamic.

Actual Result

The start_time_unix_nano remains constant across all data points when dynamic attributes are sent.

Additional context

No response

Would you like to implement a fix?

None

[emdneto]

tested with this small snippet against the main branch to reproduce the behavior;

pip install opentelemetry-api opentelemetry-sdk

import time

from opentelemetry.metrics import (
    get_meter_provider,
    set_meter_provider,
)
from opentelemetry.sdk.metrics import MeterProvider, Histogram
from opentelemetry.sdk.metrics.export import (
    ConsoleMetricExporter,
    PeriodicExportingMetricReader,
    AggregationTemporality
)

temporality = {
    Histogram: AggregationTemporality.DELTA,
}

reader = PeriodicExportingMetricReader(exporter=ConsoleMetricExporter(preferred_temporality=temporality), export_interval_millis=1_000)
provider = MeterProvider(metric_readers=[reader,])
set_meter_provider(provider)

meter = get_meter_provider().get_meter(__name__)
hist = meter.create_histogram("my_histogram", description="duration", unit="s")

if __name__ == "__main__":
    i = 0
    while True:
        time.sleep(1)
        hist.record(1, {"foo": f"bar{i}"}) # constant start_time_unix_nano
        # hist.record(1, {"foo": f"bar"}) # incremental start_time_unix_nano
        i += 1

example return python example.py | grep time

"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166783605785000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166784618787000,
"start_time_unix_nano": 1724166782606866000,
"time_unix_nano": 1724166784618787000,

[williamdoddsb365]

Thanks for reporting. Also tested with this small snippet against the main branch to reproduce the issue;

pip install opentelemetry-api opentelemetry-sdk

import time

from opentelemetry.metrics import (
    get_meter_provider,
    set_meter_provider,
)
from opentelemetry.sdk.metrics import MeterProvider, Histogram
from opentelemetry.sdk.metrics.export import (
    ConsoleMetricExporter,
    PeriodicExportingMetricReader,
    AggregationTemporality
)

temporality = {
    Histogram: AggregationTemporality.DELTA,
}

reader = PeriodicExportingMetricReader(exporter=ConsoleMetricExporter(preferred_temporality=temporality), export_interval_millis=1_000)
provider = MeterProvider(metric_readers=[reader,])
set_meter_provider(provider)

meter = get_meter_provider().get_meter(__name__)
hist = meter.create_histogram("my_histogram", description="duration", unit="s")

if __name__ == "__main__":
    i = 0
    while True:
        time.sleep(1)
        hist.record(1, {"foo": f"bar{i}"}) # constant start_time_unix_nano
        hist.record(1, {"foo": f"bar"}) # incremental start_time_unix_nano
        i += 1

Thanks for providing a more concise example.