Refactor and optimize the aggregation part of grouping stages

[zhaih]

Description

Similar approach as #43 (using a fixed size array instead of hashmap), but apply to general grouping stages as well as reduce phase

Benchmark

Showing roughly 15 - 30% gain
Baseline

Benchmark                                       (cardinality)  (labelCount)  (method)  (sampleCount)  Mode  Cnt    Score    Error  Units
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       sum            100  avgt    3    0.376 ±  0.040  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       sum           1000  avgt    3    2.264 ±  0.695  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       avg            100  avgt    3    0.386 ±  0.040  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       avg           1000  avgt    3    2.296 ±  1.805  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       sum            100  avgt    3   25.300 ±  9.160  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       sum           1000  avgt    3  209.194 ± 20.337  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       avg            100  avgt    3   26.020 ±  6.213  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       avg           1000  avgt    3  206.281 ± 35.858  ms/op

PR

Benchmark                                       (cardinality)  (labelCount)  (method)  (sampleCount)  Mode  Cnt    Score    Error  Units
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       sum            100  avgt    3    0.291 ±  0.038  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       sum           1000  avgt    3    1.320 ±  0.072  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       avg            100  avgt    3    0.333 ±  0.025  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping            100            20       avg           1000  avgt    3    1.708 ±  0.263  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       sum            100  avgt    3   15.921 ±  1.266  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       sum           1000  avgt    3  119.415 ±  4.327  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       avg            100  avgt    3   20.678 ±  2.058  ms/op
GroupingSampleStageBenchmark.benchmarkGrouping          10000            20       avg           1000  avgt    3  170.672 ± 10.899  ms/op

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[codecov]

Codecov Report

❌ Patch coverage is 93.26923% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.16%. Comparing base (8cdcce1) to head (4232d45).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...va/org/opensearch/tsdb/lang/m3/stage/AvgStage.java	83.33%	0 Missing and 1 partial ⚠️
...va/org/opensearch/tsdb/lang/m3/stage/MaxStage.java	83.33%	0 Missing and 1 partial ⚠️
...va/org/opensearch/tsdb/lang/m3/stage/MinStage.java	83.33%	0 Missing and 1 partial ⚠️
...g/opensearch/tsdb/lang/m3/stage/MultiplyStage.java	83.33%	0 Missing and 1 partial ⚠️
...ch/tsdb/lang/m3/stage/PercentileOfSeriesStage.java	91.66%	0 Missing and 1 partial ⚠️
.../org/opensearch/tsdb/lang/m3/stage/RangeStage.java	83.33%	0 Missing and 1 partial ⚠️
...va/org/opensearch/tsdb/lang/m3/stage/SumStage.java	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #100      +/-   ##
============================================
+ Coverage     89.13%   89.16%   +0.03%     
+ Complexity     5035     5030       -5     
============================================
  Files           322      324       +2     
  Lines         15518    15547      +29     
  Branches       2337     2344       +7     
============================================
+ Hits          13832    13863      +31     
+ Misses         1017     1009       -8     
- Partials        669      675       +6     

Flag	Coverage Δ
unittests	89.16% <93.26%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...g/m3/stage/AbstractGroupingDoubleBucketsStage.java	100.00% <100.00%> (ø)
...g/m3/stage/AbstractGroupingSampleBucketsStage.java	100.00% <100.00%> (ø)
...sdb/lang/m3/stage/AbstractGroupingSampleStage.java	100.00% <100.00%> (+1.14%)	⬆️
...va/org/opensearch/tsdb/lang/m3/stage/AvgStage.java	94.11% <83.33%> (-2.76%)	⬇️
...va/org/opensearch/tsdb/lang/m3/stage/MaxStage.java	95.45% <83.33%> (+0.21%)	⬆️
...va/org/opensearch/tsdb/lang/m3/stage/MinStage.java	95.45% <83.33%> (+0.21%)	⬆️
...g/opensearch/tsdb/lang/m3/stage/MultiplyStage.java	95.45% <83.33%> (+0.21%)	⬆️
...ch/tsdb/lang/m3/stage/PercentileOfSeriesStage.java	93.10% <91.66%> (-0.65%)	⬇️
.../org/opensearch/tsdb/lang/m3/stage/RangeStage.java	97.05% <83.33%> (-2.95%)	⬇️
...va/org/opensearch/tsdb/lang/m3/stage/SumStage.java	95.45% <83.33%> (+0.21%)	⬆️

... and 3 files with indirect coverage changes

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