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Add basic ExemplarFilter doc. (#4246) 

Co-authored-by: Utkarsh Umesan Pillai <utpilla@microsoft.com>
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Cijo Thomas 2023-02-28 21:05:50 -08:00 committed by GitHub
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9
docs/metrics/customizing-the-sdk/README.md
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@ -447,6 +447,15 @@ using var meterProvider = Sdk.CreateMeterProviderBuilder()
> As of today, there is no separate toggle for enable/disable Exemplar
feature. It can be turned off by using `AlwaysOffExemplarFilter`.
If the built-in `ExemplarFilter`s are not meeting the needs, one may author
custom `ExemplarFilter` as shown
[here](../extending-the-sdk/README.md#exemplarfilter). A custom filter, which
eliminates all un-interesting measurements from becoming Exemplar is a
recommended way to control performance overhead associated with collecting
Exemplars. See
[benchmark](../../../test/Benchmarks/Metrics/ExemplarBenchmarks.cs) to see how
much impact can `ExemplarFilter` have on performance.
#### ExemplarReservoir
`ExemplarReservoir` receives the measurements sampled in by the `ExemplarFilter`

46
docs/metrics/extending-the-sdk/README.md
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@ -2,7 +2,8 @@
* [Building your own exporter](#exporter)
* [Building your own reader](#reader)
* [Building your own exemplar](#exemplar)
* [Building your own exemplar filter](#exemplarfilter)
* [Building your own exemplar reservoir](#exemplarreservoir)
* [References](#references)
## Exporter
@ -70,7 +71,48 @@ to the `MeterProvider` as shown in the example [here](./Program.cs).
Not supported.
## Exemplar
## ExemplarFilter
OpenTelemetry .NET SDK has provided the following built-in `ExemplarFilter`s:
* [AlwaysOnExemplarFilter](../../../src/OpenTelemetry/Metrics/Exemplar/AlwaysOnExemplarFilter.cs)
* [AlwaysOffExemplarFilter](../../../src/OpenTelemetry/Metrics/Exemplar/AlwaysOffExemplarFilter.cs)
* [TraceBasedExemplarFilter](../../../src/OpenTelemetry/Metrics/Exemplar/TraceBasedExemplarFilter.cs)
Custom exemplar filters can be implemented to achieve filtering based on other criterion:
* `ExemplarFilter` should derive from `OpenTelemetry.ExemplarFilter` (which
belongs to the [OpenTelemetry](../../../src/OpenTelemetry/README.md) package)
and implement the `ShouldSample` method.
One example is a filter, which filters all measurements of value lower
than given threshold is given below. Such a filter prevents any measurements
below the given threshold from ever becoming a `Exemplar`. Such filters could
also incorporate the `TraceBasedExemplarFilter` condition as well, as storing
exemplars for non-sampled traces may be undesired.
```csharp
public sealed class HighValueFilter : ExemplarFilter
{
private readonly double maxValue;
public HighValueFilter(double maxValue)
{
this.maxValue = maxValue;
}
public override bool ShouldSample(long value, ReadOnlySpan<KeyValuePair<string, object>> tags)
{
return Activity.Current?.Recorded && value > this.maxValue;
}
public override bool ShouldSample(double value, ReadOnlySpan<KeyValuePair<string, object>> tags)
{
return Activity.Current?.Recorded && value > this.maxValue;
}
}
```
## ExemplarReservoir
Not supported.