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 6 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.