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Metrics SDK - consolidate the aggregation/aggregator term #2153

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Nov 29, 2021
Merged

Metrics SDK - consolidate the aggregation/aggregator term #2153

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Metrics SDK - consolidate the aggregation/aggregator term
reyang Nov 23, 2021
7112cd5
add a note to reserve aggregator term
reyang Nov 23, 2021
ea50d0b
rewrap
reyang Nov 24, 2021
7278fbb
Merge branch 'main' into reyang/metrics-sdk-aggregation-term
jmacd Nov 29, 2021
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38 changes: 23 additions & 15 deletions specification/metrics/sdk.md
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Original file line number Diff line number Diff line change
Expand Up @@ -277,6 +277,10 @@ informs the SDK on the ways and means to compute
[Aggregated Metrics](./datamodel.md#opentelemetry-protocol-data-model)
from incoming Instrument [Measurements](./api.md#measurement).

Note: the term _aggregation_ is used instead of _aggregator_. It is recommended
that implementors reserve the "aggregator" term for the future when the SDK
allows custom aggregation implementations.

An `Aggregation` specifies an operation
(i.e. [decomposable aggregate function](https://en.wikipedia.org/wiki/Aggregate_function#Decomposable_aggregate_functions)
like Sum, Histogram, Min, Max, Count)
Expand Down Expand Up @@ -387,9 +391,9 @@ This Aggregation informs the SDK to collect:

#### Histogram Aggregation

The Histogram Aggregation informs the SDK to select the best
Histogram Aggregation available.
i.e. [Explicit Bucket Histogram Aggregator](./sdk.md#explicit-bucket-histogram-aggregation).
The Histogram Aggregation informs the SDK to select the best Histogram
Aggregation available. i.e. [Explicit Bucket Histogram
Aggregation](./sdk.md#explicit-bucket-histogram-aggregation).

This Aggregation does not have any configuration parameters.

Expand All @@ -406,8 +410,8 @@ This Aggregation honors the following configuration parameters:
| Boundaries | double\[\] | [ 0, 5, 10, 25, 50, 75, 100, 250, 500, 1000 ] | Array of increasing values representing explicit bucket boundary values.<br><br>The Default Value represents the following buckets:<br>(-&infin;, 0], (0, 5.0], (5.0, 10.0], (10.0, 25.0], (25.0, 50.0], (50.0, 75.0], (75.0, 100.0], (100.0, 250.0], (250.0, 500.0], (500.0, 1000.0], (1000.0, +&infin;) |
| RecordMinMax | true, false | true | Whether to record min and max. |

Note: This aggregator should not fill out `sum` when used with instruments
that record negative measurements, e.g. `UpDownCounter` or `ObservableGauge`.
Note: This aggregation should not fill out `sum` when used with instruments that
record negative measurements, e.g. `UpDownCounter` or `ObservableGauge`.

This Aggregation informs the SDK to collect:

Expand Down Expand Up @@ -440,12 +444,15 @@ information:

A Metric SDK MUST provide a mechanism to sample `Exemplar`s from measurements.

A Metric SDK MUST allow `Exemplar` sampling to be disabled. In this instance the SDK SHOULD not have overhead related to exemplar sampling.
A Metric SDK MUST allow `Exemplar` sampling to be disabled. In this instance
the SDK SHOULD not have overhead related to exemplar sampling.

A Metric SDK MUST sample `Exemplar`s only from measurements within the context of a sampled trace BY DEFAULT.
A Metric SDK MUST sample `Exemplar`s only from measurements within the context
of a sampled trace BY DEFAULT.

A Metric SDK MUST allow exemplar sampling to leverage the configuration of a metric aggregator.
For example, Exemplar sampling of histograms should be able to leverage bucket boundaries.
A Metric SDK MUST allow exemplar sampling to leverage the configuration of a
metric aggregation. For example, Exemplar sampling of histograms should be able
to leverage bucket boundaries.

A Metric SDK SHOULD provide extensible hooks for Exemplar sampling, specifically:

Expand Down Expand Up @@ -507,14 +514,15 @@ The SDK will come with two types of built-in exemplar reservoirs:
1. SimpleFixedSizeExemplarReservoir
2. AlignedHistogramBucketExemplarReservoir

By default, explicit bucket histogram aggregators with more than 1 bucket will
use `AlignedHistogramBucketExemplarReservoir`. All other aggregators will
use `SimpleFixedSizeExemplarReservoir`.
By default, explicit bucket histogram aggregation with more than 1 bucket will
use `AlignedHistogramBucketExemplarReservoir`. All other aggregations will use
`SimpleFixedSizeExemplarReservoir`.

*SimpleExemplarReservoir*
This Exemplar reservoir MAY take a configuration parameter for the size of
the reservoir pool. The reservoir will accept measurements using an equivalent of
the [naive reservoir sampling algorithm](https://en.wikipedia.org/wiki/Reservoir_sampling)
This Exemplar reservoir MAY take a configuration parameter for the size of the
reservoir pool. The reservoir will accept measurements using an equivalent of
the [naive reservoir sampling
algorithm](https://en.wikipedia.org/wiki/Reservoir_sampling)

```
bucket = random_integer(0, num_measurements_seen)
Expand Down