[chore][exporter/splunkhec] reuse metric buffer

[atoulme]

Description:
Reuse the byte buffer used when encoding metrics to HEC events JSON.

Before:

goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/splunkhecexporter
Benchmark_pushMetricData_10_10_1024-10                                      7065            160183 ns/op          188811 B/op       1908 allocs/op
Benchmark_pushMetricData_10_10_8K-10                                        4526            261482 ns/op          906868 B/op       1909 allocs/op
Benchmark_pushMetricData_10_10_2M-10                                          91          14968551 ns/op        209815280 B/op      1919 allocs/op
Benchmark_pushMetricData_10_200_2M-10                                          2         659743354 ns/op        4196565376 B/op    38200 allocs/op
Benchmark_pushMetricData_100_200_2M-10                                         1        4331601167 ns/op        41966510248 B/op          380454 allocs/op
Benchmark_pushMetricData_100_200_5M-10                                         1        7943292125 ns/op        104884261848 B/op         380888 allocs/op
Benchmark_pushMetricData_compressed_10_10_1024-10                           3387            327217 ns/op          190565 B/op       1908 allocs/op
Benchmark_pushMetricData_compressed_10_10_8K-10                             2617            472772 ns/op          911666 B/op       1910 allocs/op
Benchmark_pushMetricData_compressed_10_10_2M-10                              100          10008019 ns/op        209853305 B/op      1915 allocs/op
Benchmark_pushMetricData_compressed_10_200_2M-10                               6         195419910 ns/op        4196171762 B/op    38060 allocs/op
Benchmark_pushMetricData_compressed_100_200_2M-10                              1        3452146542 ns/op        41961539632 B/op          380322 allocs/op
Benchmark_pushMetricData_compressed_100_200_5M-10                              1        8482437541 ns/op        104876172816 B/op         380973 allocs/op
Benchmark_pushMetricData_10_10_1024_MultiMetric-10                          3534            342315 ns/op          249470 B/op       3933 allocs/op
Benchmark_pushMetricData_10_10_8K_MultiMetric-10                            3778            341417 ns/op          249446 B/op       3933 allocs/op
Benchmark_pushMetricData_10_10_2M_MultiMetric-10                            3476            349783 ns/op          249450 B/op       3933 allocs/op
Benchmark_pushMetricData_10_200_2M_MultiMetric-10                            160           8013584 ns/op         4999122 B/op      78080 allocs/op
Benchmark_pushMetricData_100_200_2M_MultiMetric-10                            18          66614023 ns/op        49834769 B/op     780374 allocs/op
Benchmark_pushMetricData_100_200_5M_MultiMetric-10                            18          67741248 ns/op        49833329 B/op     780364 allocs/op
Benchmark_pushMetricData_compressed_10_10_1024_MultiMetric-10               2313            518090 ns/op          249862 B/op       3934 allocs/op
Benchmark_pushMetricData_compressed_10_10_8K_MultiMetric-10                 2253            521544 ns/op          250608 B/op       3934 allocs/op
Benchmark_pushMetricData_compressed_10_10_2M_MultiMetric-10                 2320            523312 ns/op          250555 B/op       3934 allocs/op
Benchmark_pushMetricData_compressed_10_200_2M_MultiMetric-10                  96          10784471 ns/op         4994520 B/op      78077 allocs/op
Benchmark_pushMetricData_compressed_100_200_2M_MultiMetric-10                 10         105036258 ns/op        49735663 B/op     780372 allocs/op
Benchmark_pushMetricData_compressed_100_200_5M_MultiMetric-10                 10         104137875 ns/op        49735001 B/op     780366 allocs/op

After:

goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/splunkhecexporter
Benchmark_pushMetricData_10_10_1024-10                                      8067            137939 ns/op           87229 B/op       1809 allocs/op
Benchmark_pushMetricData_10_10_8K-10                                        8440            147844 ns/op           94443 B/op       1809 allocs/op
Benchmark_pushMetricData_10_10_2M-10                                        3724            278429 ns/op         2184478 B/op       1811 allocs/op
Benchmark_pushMetricData_10_200_2M-10                                        392           3076075 ns/op         3825066 B/op      36012 allocs/op
Benchmark_pushMetricData_100_200_2M-10                                        38          28106033 ns/op        21429249 B/op     360033 allocs/op
Benchmark_pushMetricData_100_200_5M-10                                        37          28211490 ns/op        27723782 B/op     360034 allocs/op
Benchmark_pushMetricData_compressed_10_10_1024-10                           3838            304303 ns/op           87560 B/op       1809 allocs/op
Benchmark_pushMetricData_compressed_10_10_8K-10                             3948            318874 ns/op           95140 B/op       1809 allocs/op
Benchmark_pushMetricData_compressed_10_10_2M-10                             2132            499910 ns/op         2184845 B/op       1811 allocs/op
Benchmark_pushMetricData_compressed_10_200_2M-10                             176           6691759 ns/op         3816367 B/op      36012 allocs/op
Benchmark_pushMetricData_compressed_100_200_2M-10                             18          64509919 ns/op        19294689 B/op     360015 allocs/op
Benchmark_pushMetricData_compressed_100_200_5M-10                             16          64694784 ns/op        22449746 B/op     360015 allocs/op
Benchmark_pushMetricData_10_10_1024_MultiMetric-10                          3382            347123 ns/op          249432 B/op       3933 allocs/op
Benchmark_pushMetricData_10_10_8K_MultiMetric-10                            3392            350381 ns/op          249390 B/op       3933 allocs/op
Benchmark_pushMetricData_10_10_2M_MultiMetric-10                            3488            349640 ns/op          249388 B/op       3933 allocs/op
Benchmark_pushMetricData_10_200_2M_MultiMetric-10                            156           7492550 ns/op         4999467 B/op      78080 allocs/op
Benchmark_pushMetricData_100_200_2M_MultiMetric-10                            15          68214128 ns/op        49880567 B/op     780369 allocs/op
Benchmark_pushMetricData_100_200_5M_MultiMetric-10                            16          68479602 ns/op        49862135 B/op     780361 allocs/op
Benchmark_pushMetricData_compressed_10_10_1024_MultiMetric-10               2286            521065 ns/op          249857 B/op       3934 allocs/op
Benchmark_pushMetricData_compressed_10_10_8K_MultiMetric-10                 2230            533990 ns/op          250965 B/op       3934 allocs/op
Benchmark_pushMetricData_compressed_10_10_2M_MultiMetric-10                 2216            519334 ns/op          251729 B/op       3934 allocs/op
Benchmark_pushMetricData_compressed_10_200_2M_MultiMetric-10                 100          10730782 ns/op         4994400 B/op      78079 allocs/op
Benchmark_pushMetricData_compressed_100_200_2M_MultiMetric-10                 10         102336283 ns/op        49735569 B/op     780370 allocs/op
Benchmark_pushMetricData_compressed_100_200_5M_MultiMetric-10                 10         103345238 ns/op        49736361 B/op     780377 allocs/op

Benchstat results:

goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/splunkhecexporter
                                                     │   before.txt   │               after.txt               │
                                                     │     sec/op     │    sec/op     vs base                 │
_pushMetricData_10_10_1024-10                            160.2µ ± ∞ ¹   137.9µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_8K-10                              261.5µ ± ∞ ¹   147.8µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_2M-10                            14968.6µ ± ∞ ¹   278.4µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_200_2M-10                           659.743m ± ∞ ¹   3.076m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_2M-10                          4331.60m ± ∞ ¹   28.11m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_5M-10                          7943.29m ± ∞ ¹   28.21m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_1024-10                 327.2µ ± ∞ ¹   304.3µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_8K-10                   472.8µ ± ∞ ¹   318.9µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_2M-10                 10008.0µ ± ∞ ¹   499.9µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_200_2M-10                195.420m ± ∞ ¹   6.692m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_2M-10               3452.15m ± ∞ ¹   64.51m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_5M-10               8482.44m ± ∞ ¹   64.69m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_1024_MultiMetric-10                342.3µ ± ∞ ¹   347.1µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_8K_MultiMetric-10                  341.4µ ± ∞ ¹   350.4µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_2M_MultiMetric-10                  349.8µ ± ∞ ¹   349.6µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_200_2M_MultiMetric-10                 8.014m ± ∞ ¹   7.493m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_2M_MultiMetric-10                66.61m ± ∞ ¹   68.21m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_5M_MultiMetric-10                67.74m ± ∞ ¹   68.48m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_1024_MultiMetric-10     518.1µ ± ∞ ¹   521.1µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_8K_MultiMetric-10       521.5µ ± ∞ ¹   534.0µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_2M_MultiMetric-10       523.3µ ± ∞ ¹   519.3µ ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_200_2M_MultiMetric-10      10.78m ± ∞ ¹   10.73m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_2M_MultiMetric-10     105.0m ± ∞ ¹   102.3m ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_5M_MultiMetric-10     104.1m ± ∞ ¹   103.3m ± ∞ ¹        ~ (p=1.000 n=1) ²
geomean                                                  13.98m         3.061m        -78.11%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05

                                                     │    before.txt     │               after.txt                │
                                                     │       B/op        │     B/op       vs base                 │
_pushMetricData_10_10_1024-10                             184.39Ki ± ∞ ¹   85.18Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_8K-10                               885.61Ki ± ∞ ¹   92.23Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_2M-10                              200.095Mi ± ∞ ¹   2.083Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_200_2M-10                            4002.157Mi ± ∞ ¹   3.648Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_2M-10                           40022.38Mi ± ∞ ¹   20.44Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_5M-10                          100025.43Mi ± ∞ ¹   26.44Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_1024-10                  186.10Ki ± ∞ ¹   85.51Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_8K-10                    890.30Ki ± ∞ ¹   92.91Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_2M-10                   200.132Mi ± ∞ ¹   2.084Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_200_2M-10                 4001.781Mi ± ∞ ¹   3.640Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_2M-10                40017.64Mi ± ∞ ¹   18.40Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_5M-10               100017.71Mi ± ∞ ¹   21.41Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_1024_MultiMetric-10                  243.6Ki ± ∞ ¹   243.6Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_8K_MultiMetric-10                    243.6Ki ± ∞ ¹   243.5Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_10_2M_MultiMetric-10                    243.6Ki ± ∞ ¹   243.5Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_10_200_2M_MultiMetric-10                   4.768Mi ± ∞ ¹   4.768Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_2M_MultiMetric-10                  47.53Mi ± ∞ ¹   47.57Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_100_200_5M_MultiMetric-10                  47.52Mi ± ∞ ¹   47.55Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_1024_MultiMetric-10       244.0Ki ± ∞ ¹   244.0Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_8K_MultiMetric-10         244.7Ki ± ∞ ¹   245.1Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_2M_MultiMetric-10         244.7Ki ± ∞ ¹   245.8Ki ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_200_2M_MultiMetric-10        4.763Mi ± ∞ ¹   4.763Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_2M_MultiMetric-10       47.43Mi ± ∞ ¹   47.43Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_5M_MultiMetric-10       47.43Mi ± ∞ ¹   47.43Mi ± ∞ ¹        ~ (p=1.000 n=1) ²
geomean                                                    25.43Mi         1.990Mi        -92.18%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05

                                                     │  before.txt  │              after.txt               │
                                                     │  allocs/op   │  allocs/op    vs base                │
_pushMetricData_10_10_1024-10                          1.908k ± ∞ ¹   1.809k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_10_10_8K-10                            1.909k ± ∞ ¹   1.809k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_10_10_2M-10                            1.919k ± ∞ ¹   1.811k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_10_200_2M-10                           38.20k ± ∞ ¹   36.01k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_100_200_2M-10                          380.5k ± ∞ ¹   360.0k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_100_200_5M-10                          380.9k ± ∞ ¹   360.0k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_1024-10               1.908k ± ∞ ¹   1.809k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_8K-10                 1.910k ± ∞ ¹   1.809k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_2M-10                 1.915k ± ∞ ¹   1.811k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_200_2M-10                38.06k ± ∞ ¹   36.01k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_2M-10               380.3k ± ∞ ¹   360.0k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_5M-10               381.0k ± ∞ ¹   360.0k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_10_10_1024_MultiMetric-10              3.933k ± ∞ ¹   3.933k ± ∞ ¹       ~ (p=1.000 n=1) ³
_pushMetricData_10_10_8K_MultiMetric-10                3.933k ± ∞ ¹   3.933k ± ∞ ¹       ~ (p=1.000 n=1) ³
_pushMetricData_10_10_2M_MultiMetric-10                3.933k ± ∞ ¹   3.933k ± ∞ ¹       ~ (p=1.000 n=1) ³
_pushMetricData_10_200_2M_MultiMetric-10               78.08k ± ∞ ¹   78.08k ± ∞ ¹       ~ (p=1.000 n=1) ³
_pushMetricData_100_200_2M_MultiMetric-10              780.4k ± ∞ ¹   780.4k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_100_200_5M_MultiMetric-10              780.4k ± ∞ ¹   780.4k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_10_10_1024_MultiMetric-10   3.934k ± ∞ ¹   3.934k ± ∞ ¹       ~ (p=1.000 n=1) ³
_pushMetricData_compressed_10_10_8K_MultiMetric-10     3.934k ± ∞ ¹   3.934k ± ∞ ¹       ~ (p=1.000 n=1) ³
_pushMetricData_compressed_10_10_2M_MultiMetric-10     3.934k ± ∞ ¹   3.934k ± ∞ ¹       ~ (p=1.000 n=1) ³
_pushMetricData_compressed_10_200_2M_MultiMetric-10    78.08k ± ∞ ¹   78.08k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_2M_MultiMetric-10   780.4k ± ∞ ¹   780.4k ± ∞ ¹       ~ (p=1.000 n=1) ²
_pushMetricData_compressed_100_200_5M_MultiMetric-10   780.4k ± ∞ ¹   780.4k ± ∞ ¹       ~ (p=1.000 n=1) ²
geomean                                                26.34k         25.62k        -2.74%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05
³ all samples are equal