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Add doc about metric limits (#2645)

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Cijo Thomas 2021-11-19 15:17:13 -08:00 committed by GitHub
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docs/metrics/customizing-the-sdk/README.md
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@ -64,7 +64,10 @@ instruments must be explicitly added to the meter provider.
`AddMeter` method on `MeterProviderBuilder` can be used to add a `Meter` to the
provider. The name of the `Meter` (case-insensitive) must be provided as an
argument to this method. `AddMeter` can be called multiple times to add more
than one meters. It also supports wild-card subscription model.
than one meters. It also supports wildcard subscription model. It is important
to note that *all* the instruments from the meter will be enabled, when a
`Meter` is added. To selectively drop some instruments from a `Meter`, use the
[View](#view) feature, as shown [here](#drop-an-instrument).
It is **not** possible to add meters *once* the provider is built by the
`Build()` method on the `MeterProviderBuilder`.
@ -268,6 +271,48 @@ for Views.
See [Program.cs](./Program.cs) for a complete example.
### Changing maximum Metric Streams
Every instrument results in the creation of a single Metric stream. With Views,
it is possible to produce more than one Metric stream from a single instrument.
To protect the SDK from unbounded memory usage, SDK limits the maximum number of
metric streams. All the measurements from the instruments created after reaching
this limit will be dropped. The default is 1000, and `SetMaxMetricStreams` can
be used to override the default.
```csharp
using OpenTelemetry;
using OpenTelemetry.Metrics;
using var meterProvider = Sdk.CreateMeterProviderBuilder()
.AddMeter("*")
.SetMaxMetricStreams(100)
.Build();
```
### Changing maximum MetricPoints per MetricStream
A Metric stream can contain as many Metric points as the number of unique
combination of keys and values. To protect the SDK from unbounded memory usage,
SDK limits the maximum number of metric points per metric stream, to a default
of 2000. Once the limit is hit, any new key/value combination for that metric is
ignored. `SetMaxMetricPointsPerMetricStream` can be used to override the
default.
```csharp
using OpenTelemetry;
using OpenTelemetry.Metrics;
using var meterProvider = Sdk.CreateMeterProviderBuilder()
.AddMeter("*")
.SetMaxMetricPointsPerMetricStream(10000)
.Build();
```
**NOTE:** The above limit is *per* metric stream, and applies to all the metric
streams. There is no ability to apply different limits for each instrument at
this moment.
### Instrumentation
// TODO