Type specific exemplar reservoirs

[jack-berg]

I'm not completely satisfied with #7742.

Its awkward that a single implementation of ExemplarReservoir has to be responsible for both longs and double, and collecting longs and doubles. In actuality, because each aggregation handle has its own reservoir instance, a particular reservoir is only responsible for recording / collecting longs OR recording / collecting doubles.

This (optional) followup to #7742 teases ExemplarReservoir apart into DoubleExemplarReservoir and LongExemplarReservoir. It also introduces a new ExemplarReservoirFactory with two methods: createLongExemplarReservoir(), createDoubleExemplarReservoir(). This would be the interface that we would ultimately add to View for user configuration.

[codecov]

Codecov Report

❌ Patch coverage is 94.20290% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.16%. Comparing base (6056b05) to head (2d2b22a).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
.../metrics/internal/aggregator/AggregatorHandle.java	76.00%	5 Missing and 1 partial ⚠️
...cs/internal/exemplar/ExemplarReservoirFactory.java	92.30%	1 Missing ⚠️
...try/sdk/metrics/internal/view/DropAggregation.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## main #7758 +/- ## ============================================ - Coverage 90.18% 90.16% -0.03%  + Complexity 7196 7189 -7  ============================================ Files 814 814 Lines 21722 21730 +8 Branches 2125 2129 +4 ============================================ + Hits 19590 19592 +2  - Misses 1465 1469 +4  - Partials 667 669 +2 

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[jkwatson]

I'm fine with this approach, too. I'll trust your judgement on which direction to go.

[jack-berg]

I'm fine with this approach, too. I'll trust your judgement on which direction to go.

I prefer this. Fortunately, we actually don't need to rush to stabilize anything related to ExemplarReservoir since there is currently no user facing configuration available around this. For the immediate future, we just need to focus on ExemplarFilter, which will have a very limited public API surface area.