[QUERY] Sampling Ratio Issue: Unexpected Number of Samples

[gensichen]

Library name and version

Azure.Monitor.OpenTelemetry.Exporter, Version=1.3.0.0,

Query/Question

Description

We are using the Azure.Monitor.OpenTelemetry to push OpenTelemetry (OTel) telemetry to Application Insights. When adjusting the Application Insights sampling ratio, we noticed unexpected behavior in the sampling item count.

Steps to Reproduce

1. Send 80 requests with a sampling ratio of 100%.
   • Expected Result: 80 samples shown in Application Insights.
   • Actual Result: 80 samples shown (as expected).
2. Immediately change the sampling ratio to 50% and send another 80 requests.
   • Expected Result: 40 samples shown in Application Insights.
   • Actual Result: 230 samples shown (unexpected).

Observations

• 80 requests with 100% sampling ratio: 80 samples shown (expected).
• 80 requests with 50% sampling ratio: 230 samples shown (unexpected, expected 40 samples).

Request for Explanation

Can you please provide an explanation for this discrepancy in the sampling results?

Environment

.NET 8.0

[github-actions]

Thank you for your feedback. Tagging and routing to the team member best able to assist.

[github-actions]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @cijothomas @rajkumar-rangaraj @reyang @TimothyMothra.

[TimothyMothra]

Hi @gensichen,

80 requests with 50% sampling ratio: 230 samples shown

This is not expected.

Can you share your full config? I'd like to see how you are configuring sampling.

We have a query in our public docs which shows how to count telemetry and we expect this should match your config:
https://learn.microsoft.com/en-us/azure/azure-monitor/app/sampling-classic-api#knowing-whether-sampling-is-in-operation