テイルベースサンプリング

public class ParentBasedElseAlwaysRecordSampler : Sampler
{
    private readonly Sampler _rootSampler;

    public ParentBasedElseAlwaysRecordSampler(Sampler rootSampler)
        : base()
    {
        _rootSampler = rootSampler ?? throw new ArgumentNullException(nameof(rootSampler));
    }

    public override SamplingResult ShouldSample(in SamplingParameters samplingParameters)
    {
        // 親がある場合、その親のサンプリング判定を使用する
        if (samplingParameters.ParentContext.TraceId != default)
        {
            if (samplingParameters.ParentContext.TraceFlags.HasFlag(ActivityTraceFlags.Recorded))
            {
                return new SamplingResult(SamplingDecision.RecordAndSample);
            }
            else
            {
                // ドロップする代わりに、プロセッサーで処理できるように
                // このアクティビティを記録する
                return new SamplingResult(SamplingDecision.RecordOnly);
            }
        }

        // これはルートアクティビティ。ルートサンプラーを使用して判定する。
        return _rootSampler.ShouldSample(samplingParameters);
    }

    public override string Description => $"ParentBasedElseAlwaysRecordSampler({_rootSampler.Description})";
}

public class TailSamplingProcessor : BaseProcessor<Activity>
{
    private readonly string _statusTagName;

    public TailSamplingProcessor(string statusTagName = "otel.status_code")
    {
        _statusTagName = statusTagName;
    }

    public override void OnEnd(Activity activity)
    {
        // アクティビティがすでにサンプリング済みの場合、何もする必要はない
        if (activity.ActivityTraceFlags.HasFlag(ActivityTraceFlags.Recorded))
        {
            return;
        }

        // エラーアクティビティかどうかを確認する
        bool isError = false;

        if (activity.Status == ActivityStatusCode.Error)
        {
            isError = true;
        }
        else if (activity.TagObjects != null)
        {
            foreach (var tag in activity.TagObjects)
            {
                if (tag.Key == _statusTagName)
                {
                    if (tag.Value?.ToString() == "ERROR")
                    {
                        isError = true;
                        break;
                    }
                }
            }
        }

        if (isError)
        {
            Console.WriteLine($"Including error activity with id {activity.Id} and status {activity.Status}");
            activity.ActivityTraceFlags |= ActivityTraceFlags.Recorded;
        }
        else
        {
            Console.WriteLine($"Dropping activity with id {activity.Id} and status {activity.Status}");
        }
    }
}

Including error activity with id
00-404ddff248b8f9a9b21e347d68d2640e-035858bc3c168885-01 and status Error
Activity.TraceId:            404ddff248b8f9a9b21e347d68d2640e
Activity.SpanId:             035858bc3c168885
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: SDK.TailSampling.POC
Activity.DisplayName:        SayHello
Activity.Kind:               Internal
Activity.StartTime:          2023-02-09T19:05:32.5563112Z
Activity.Duration:           00:00:00.0028144
Activity.Tags:
    foo: bar
StatusCode: Error
Resource associated with Activity:
    service.name: unknown_service:Examples.TailBasedSamplingAtSpanLevel

Dropping activity with id 00-ea861bda268c58d328ab7cbe49851499-daba29055de80a53-00
and status Ok

Including head-sampled activity with id
00-f3c88010615e285c8f3cb3e2bcd70c7f-f9316215f12437c3-01 and status Ok
Activity.TraceId:            f3c88010615e285c8f3cb3e2bcd70c7f
Activity.SpanId:             f9316215f12437c3
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: SDK.TailSampling.POC
Activity.DisplayName:        SayHello
Activity.Kind:               Internal
Activity.StartTime:          2023-02-09T19:05:32.8519346Z
Activity.Duration:           00:00:00.0000034
Activity.Tags:
    foo: bar
StatusCode: Ok
Resource associated with Activity:
    service.name: unknown_service:Examples.TailBasedSamplingAtSpanLevel