opentelemetry-dotnet/docs/trace/building-your-own-sampler/README.md

Building your own Sampler

• Samplers should inherit from Sampler, and implement ShouldSample method.
• ShouldSample should not block or take long time, since it will be called on critical code path.

internal class MySampler : Sampler
{
    public override SamplingResult ShouldSample(in SamplingParameters samplingParameters)
    {
        return new SamplingResult(SamplingDecision.RecordAndSampled);
    }
}