[coreinternal/pdatautil] Reduce allocations in Map/ValueHash functions

[dmitryax]

Use a buffer pool instead of making allocations each time. The remaining allocations are caused by sort.Strings and pdata.BytesSlice.AsRaw.

Before:

goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal/pdatautil
BenchmarkMapHashFourItems
BenchmarkMapHashFourItems-10                  	 3136358	       383.7 ns/op	     288 B/op	      11 allocs/op
BenchmarkMapHashEightItems
BenchmarkMapHashEightItems-10                 	 1588498	       777.5 ns/op	     456 B/op	      19 allocs/op
BenchmarkMapHashWithEmbeddedSliceAndMap
BenchmarkMapHashWithEmbeddedSliceAndMap-10    	  933703	      1295 ns/op	     784 B/op	      32 allocs/op
PASS

After:

pkg: github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal/pdatautil
BenchmarkMapHashFourItems
BenchmarkMapHashFourItems-10                  	 5163958	       226.0 ns/op	      24 B/op	       1 allocs/op
BenchmarkMapHashEightItems
BenchmarkMapHashEightItems-10                 	 2389960	       502.4 ns/op	      32 B/op	       2 allocs/op
BenchmarkMapHashWithEmbeddedSliceAndMap
BenchmarkMapHashWithEmbeddedSliceAndMap-10    	 1497609	       799.8 ns/op	      56 B/op	       3 allocs/op
PASS

[runforesight]

Foresight Summary

    
Major Impacts

TestValueHash ❌ failed 1 times in 4 runs (25% fail rate).

TestValueHash/empty_bytes ❌ failed 1 times in 4 runs (25% fail rate).

build-and-test-windows duration(5 seconds) has decreased 42 minutes 27 seconds compared to main branch avg(42 minutes 32 seconds).

View More Details

⭕  changelog workflow has finished in 3 seconds (2 minutes 1 second less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
changelog	-     🔗	N/A	See Details

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⭕  build-and-test-windows workflow has finished in 5 seconds (42 minutes 27 seconds less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
windows-unittest-matrix	-     🔗	N/A	See Details
windows-unittest	-     🔗	N/A	See Details

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✅  check-links workflow has finished in 39 seconds (57 seconds less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
changed files	-     🔗	N/A	See Details
check-links	-     🔗	N/A	See Details

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✅  telemetrygen workflow has finished in 55 seconds (1 minute 19 seconds less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
publish-latest	-     🔗	N/A	See Details
build-dev	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details

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✅  tracegen workflow has finished in 1 minute (1 minute 11 seconds less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
build-dev	-     🔗	N/A	See Details
publish-latest	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details

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✅  prometheus-compliance-tests workflow has finished in 3 minutes 14 seconds (4 minutes 15 seconds less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
prometheus-compliance-tests	-     🔗	✅ 21  ❌ 0  ⏭ 0    🔗	See Details

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✅  build-and-test workflow has finished in 37 minutes 8 seconds (10 minutes 4 seconds less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
unittest-matrix (1.19, internal)	-     🔗	✅ 651  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, internal)	-     🔗	✅ 651  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, processor)	-     🔗	✅ 1481  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, processor)	-     🔗	✅ 1481  ❌ 0  ⏭ 0    🔗	See Details
correctness-metrics	-     🔗	✅ 2  ❌ 0  ⏭ 0    🔗	See Details
correctness-traces	-     🔗	✅ 17  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, extension)	-     🔗	✅ 528  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, extension)	-     🔗	✅ 528  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-0)	-     🔗	✅ 2565  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, receiver-0)	-     🔗	✅ 2565  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, exporter)	-     🔗	✅ 2468  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, exporter)	-     🔗	✅ 2468  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, other)	-     🔗	✅ 4454  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, other)	-     🔗	✅ 4454  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-1)	-     🔗	✅ 1894  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, receiver-1)	-     🔗	✅ 1894  ❌ 0  ⏭ 0    🔗	See Details
integration-tests	-     🔗	✅ 55  ❌ 0  ⏭ 0    🔗	See Details
setup-environment	-     🔗	N/A	See Details
checks	-     🔗	N/A	See Details
check-codeowners	-     🔗	N/A	See Details
check-collector-module-version	-     🔗	N/A	See Details
lint-matrix (receiver-0)	-     🔗	N/A	See Details
lint-matrix (receiver-1)	-     🔗	N/A	See Details
lint-matrix (processor)	-     🔗	N/A	See Details
lint-matrix (exporter)	-     🔗	N/A	See Details
lint-matrix (extension)	-     🔗	N/A	See Details
lint-matrix (internal)	-     🔗	N/A	See Details
lint-matrix (other)	-     🔗	N/A	See Details
build-examples	-     🔗	N/A	See Details
lint	-     🔗	N/A	See Details
unittest (1.19)	-     🔗	N/A	See Details
unittest (1.18)	-     🔗	N/A	See Details
cross-compile (darwin, amd64)	-     🔗	N/A	See Details
cross-compile (darwin, arm64)	-     🔗	N/A	See Details
cross-compile (linux, 386)	-     🔗	N/A	See Details
cross-compile (linux, amd64)	-     🔗	N/A	See Details
cross-compile (linux, arm)	-     🔗	N/A	See Details
cross-compile (linux, arm64)	-     🔗	N/A	See Details
cross-compile (windows, 386)	-     🔗	N/A	See Details
cross-compile (linux, ppc64le)	-     🔗	N/A	See Details
cross-compile (windows, amd64)	-     🔗	N/A	See Details
build-package (deb)	-     🔗	N/A	See Details
build-package (rpm)	-     🔗	N/A	See Details
windows-msi	-     🔗	N/A	See Details
publish-check	-     🔗	N/A	See Details
publish-dev	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details

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✅  load-tests workflow has finished in 7 minutes 54 seconds (6 minutes 25 seconds less than main branch avg.) and finished at 16th Jan, 2023.

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Job	Failed Steps	Tests
loadtest (TestTraceAttributesProcessor)	-     🔗	✅ 3  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestIdleMode)	-     🔗	✅ 1  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetric10kDPS|TestMetricsFromFile)	-     🔗	✅ 6  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceNoBackend10kSPS|TestTrace1kSPSWithAttrs)	-     🔗	✅ 8  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetricResourceProcessor|TestTrace10kSPS)	-     🔗	✅ 12  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceBallast1kSPSWithAttrs|TestTraceBallast1kSPSAddAttrs)	-     🔗	✅ 10  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestBallastMemory|TestLog10kDPS)	-     🔗	✅ 19  ❌ 0  ⏭ 0    🔗	See Details
setup-environment	-     🔗	N/A	See Details

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[MovieStoreGuy]

This looks fine, the only concern I had which I checked isn't the case is trying to borrow the underlying slice which can lead to some weirdness on Reset.