ddsketch from histogram seems inaccurate

[tony-resendiz]

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Problem

hello, not sure if this is a bug or the intended behavior so i apologize if this is categorized incorrectly.

this issue is related to this discussion. the tl;dr is that when i record histograms of value 1 i see those averages around ~1.5 in datadog. it seems a result of this code where the dd sketch is built from bucket boundaries.

id like to propose updating the sketch sum, count, and avg fields from the histogram sum and count fields and would be happy to make a PR.

thanks for your time.

Configuration

[log_schema]
level_key = "status"
level = "info"

[api]
enabled = true
address = "0.0.0.0:8787"
playground = false

[sources.opentelemetry]
type = "opentelemetry"
grpc.address = "0.0.0.0:4317"
http.address = "0.0.0.0:4318"

[sinks.datadog_metrics_sink]
type = "datadog_metrics"
inputs = ["opentelemetry.metrics"]
default_api_key = "${DD_API_KEY}"
endpoint = "https://metrics.agent.datadoghq.com"

Version

0.51.1

Debug Output

Example Data

vector tap histogram event (sum = 2, count = 2, avg should be 1)

{
  "name": "test.default.vector.histogram",
  "tags": {
    "resource.service.name": "unknown_service",
    "resource.telemetry.sdk.language": "python",
    "resource.telemetry.sdk.name": "opentelemetry",
    "resource.telemetry.sdk.version": "1.38.0",
    "scope.name": "my-meter"
  },
  "timestamp": "2025-11-17T19:05:45.509186114Z",
  "kind": "incremental",
  "aggregated_histogram": {
    "buckets": [
      {
        "upper_limit": 0.0,
        "count": 0
      },
      {
        "upper_limit": 5.0,
        "count": 2
      },
      {
        "upper_limit": 10.0,
        "count": 0
      },
      {
        "upper_limit": 25.0,
        "count": 0
      },
      {
        "upper_limit": 50.0,
        "count": 0
      },
      {
        "upper_limit": 75.0,
        "count": 0
      },
      {
        "upper_limit": 100.0,
        "count": 0
      },
      {
        "upper_limit": 250.0,
        "count": 0
      },
      {
        "upper_limit": 500.0,
        "count": 0
      },
      {
        "upper_limit": 750.0,
        "count": 0
      },
      {
        "upper_limit": 1000.0,
        "count": 0
      },
      {
        "upper_limit": 2500.0,
        "count": 0
      },
      {
        "upper_limit": 5000.0,
        "count": 0
      },
      {
        "upper_limit": 7500.0,
        "count": 0
      },
      {
        "upper_limit": 10000.0,
        "count": 0
      },
      {
        "upper_limit": "inf",
        "count": 0
      }
    ],
    "count": 2,
    "sum": 2.0
  }
}

instead of avg=1 i see a dd-sketch request like this:

[22/Nov/2025 00:49:53] "POST /api/beta/sketches HTTP/1.1" 200 -

==== /api/beta/sketches ====
Sketch[0] metric=test.default.vector.histogram
  host=''
  tags=['resource.service.name:unknown_service', 'resource.telemetry.sdk.language:python', 'resource.telemetry.sdk.name:opentelemetry', 'resource.telemetry.sdk.version:1.38.0', 'scope.name:my-meter']
    dogsketch[0]: ts=1763772591, cnt=2, sum=2.5351459064147286, avg=1.2675729532073643, min=0.0, max=2.5351459064147286, k_len=2, n_len=2

Additional Context

No response

References

#24282