probabilisticsamplerprocessor: should sampling.priority drop Spans

[shawnsong]

Context

When adding probabilisticsamplerprocessor to our collector, I realized that all Spans with sampling.priority set to 0 are dropped by the processor.

We use a parent-based sampler in our application code and we add sampling.priority=0 to all Spans by default to prevent Spans from starting from everywhere (for example we don't want any traces for health checks and some scheduled jobs).

Is it possible to have this processor respect the decision of a Span's parent if it exists?

[jpkrohling]

Sorry, I'm not sure I understand it. Are you saying that this processor isn't dropping spans with sampling.priority=0? Can you share your config and a couple of spans, with your expectation on what should happen to them? Or better yet, can you create a unit test demonstrating the problem? The suite does seem to have tests covering this case, but I'm really interested in this if you can provide a reproducer.

opentelemetry-collector-contrib/processor/probabilisticsamplerprocessor/probabilisticsampler_test.go

Lines 270 to 298 in 3ba302b

	name: "must_not_sample",
	cfg: &Config{
	ProcessorSettings: config.NewProcessorSettings(config.NewComponentID(typeStr)),
	SamplingPercentage: 100.0,
	},
	td: singleSpanWithAttrib(
	"sampling.priority",
	pcommon.NewValueInt(0)),
	},
	{
	name: "must_not_sample_double",
	cfg: &Config{
	ProcessorSettings: config.NewProcessorSettings(config.NewComponentID(typeStr)),
	SamplingPercentage: 100.0,
	},
	td: singleSpanWithAttrib(
	"sampling.priority",
	pcommon.NewValueDouble(0)),
	},
	{
	name: "must_not_sample_string",
	cfg: &Config{
	ProcessorSettings: config.NewProcessorSettings(config.NewComponentID(typeStr)),
	SamplingPercentage: 100.0,
	},
	td: singleSpanWithAttrib(
	"sampling.priority",
	pcommon.NewValueString("0")),
	},