Bug: Sampling Include & Exclude

[TimothyMothra]

Problem

When configuring Sampling, we allow users to set both the Include and Exclude properties.
This is a logical fallacy because this is a binary decision. An item cannot be both included and excluded.

In our current implementation, the Excluded types will always win over the Included types.
(we actually have a test to guarantee this behavior).

Exclude:

ApplicationInsights-dotnet/src/ServerTelemetryChannel/SamplingTelemetryProcessor.cs

Lines 80 to 84 in 981feb7

	set
	{
	this.excludedTypesString = value;
	this.excludedTypesFlags = this.PopulateSamplingFlagsFromTheInput(value);
	}

Include:

ApplicationInsights-dotnet/src/ServerTelemetryChannel/SamplingTelemetryProcessor.cs

Lines 99 to 103 in 981feb7

	set
	{
	this.includedTypesString = value;
	this.includedTypesFlags = this.PopulateSamplingFlagsFromTheInput(value);
	}

Evaluation:

ApplicationInsights-dotnet/src/ServerTelemetryChannel/SamplingTelemetryProcessor.cs

Lines 282 to 296 in 981feb7

	private bool IsSamplingApplicable(SamplingTelemetryItemTypes telemetryItemTypeFlag)
	{
	if (this.excludedTypesFlags.HasFlag(telemetryItemTypeFlag))
	{
	return false;
	}
	if (this.includedTypesFlags != SamplingTelemetryItemTypes.None && !this.includedTypesFlags.HasFlag(telemetryItemTypeFlag))
	{
	return false;
	}
	return true;
	}
	}

Test:

ApplicationInsights-dotnet/Test/ServerTelemetryChannel.Test/Shared.Tests/SamplingTelemetryProcessorTest.cs

Lines 327 to 339 in 981feb7

	[TestMethod]
	public void IncludedDoNotOverrideExcludedFromSampling()
	{
	TelemetryTypeDoesNotSupportSampling(
	telemetryProcessors =>
	{
	telemetryProcessors.Process(new PageViewTelemetry());
	telemetryProcessors.Process(new RequestTelemetry());
	return 2;
	},
	"pageview;request",
	"exception;request");
	}

Proposal

I want to simplify our internal types and codify the assumptions we're making in our evaluation method.

• Store only one list of includedTypes
• If a user sets Include or Exclude, no change. (This is correct.)
• If a user sets both Include and Exclude in their config (This is incorrect.)
  • Setting Exclude will always take priority over Include (no change to behavior).
  • New: emit a new event source warning: "Configuration Error: Exclude will take precedence over Include.".