# Tail-based sampling **URL:** \ **Category:** APM\ **Tags:** dotnet, server\ **Created:** [July 31, 2023, 2:13pm UTC](https://discuss.elastic.co/t/tail-based-sampling/339701 "2023-07-31T14:13:41Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Bertrand67](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bertrand67/32/124123_2.png) [@Bertrand67](https://discuss.elastic.co/u/Bertrand67)\ **Post date:** [July 31, 2023, 2:13pm UTC](https://discuss.elastic.co/t/tail-based-sampling/339701/1 "2023-07-31T14:13:41Z")
**Kibana version** : 8.7.0 **Elasticsearch version** : 8.7.0 **APM Agent language and version** : .NET **Description of the problem including expected versus actual behavior. Please include screenshots (if relevant)**: Hello, I've configured tail-based sampling on server using this configuration : ```auto - sample_rate: 1 trace.outcome: "failure" - sample_rate: .01 ``` But when I look in Kibana, I always see all traces including transactions and spans data for succesful traces. What is a proper configuration client/server side to have only 1% of sampled traces ? I use the .NET Elastic API to start and close transactions. I hope sampling is not based on "IsSampled" property because it's always "true" and it cannot be determined client side if sampling is configured in tail-based mode on server side. Thanks in advance, ---
**Author:** ![simitt](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/simitt/32/106406_2.png) [@simitt](https://discuss.elastic.co/u/simitt)\ **Post date:** [August 1, 2023, 5:54am UTC](https://discuss.elastic.co/t/tail-based-sampling/339701/2 "2023-08-01T05:54:49Z")
With tail based sampling, whether a trace is sampled or not, is decided based on the _root transaction_. The root transaction is the very first transaction in a distributed trace. You can identify root transactions as transactions who do not have a `parent.id` set. The sampling rate is defined for `trace.outcome` , which means `event.outcome` of the root transaction. With the configuration that you shared, all traces (transactions+spans) where the root transaction has a `event.outcome: failure` are going to be 100% sampled, independent of the `event.outcome` of the other transactions in this trace. And traces (transactions+spans) where the root transaction has any other value for `event.outcome`, are sampled with 1%. Can you please verify the sampling again with looking at the `root` transactions? ---
**Author:** ![Bertrand67](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bertrand67/32/124123_2.png) [@Bertrand67](https://discuss.elastic.co/u/Bertrand67)\ **Post date:** [August 1, 2023, 12:25pm UTC](https://discuss.elastic.co/t/tail-based-sampling/339701/3 "2023-08-01T12:25:56Z")
Hello, I've made more than 20 calls where root transactions has `event.outcome` equal to `success` and all traces are visible in Kibana including transactions and spans data. We are using an old version of NuGet Package **Elastic.Apm** : version **1.8.1** , maybe this version doesn't support tail-based sampling ? Thank you for your help, ---
**Author:** ![Bertrand67](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bertrand67/32/124123_2.png) [@Bertrand67](https://discuss.elastic.co/u/Bertrand67)\ **Post date:** [August 1, 2023, 12:40pm UTC](https://discuss.elastic.co/t/tail-based-sampling/339701/4 "2023-08-01T12:40:30Z")
I've got news. It's eventually working today ! I don't know why the situation changed. Maybe applications rebooting solved the problem. Sorry for the disturbance. Thank you for your time, ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [August 29, 2023, 12:40pm UTC](https://discuss.elastic.co/t/tail-based-sampling/339701/5 "2023-08-29T12:40:33Z")
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