opentelemetry-sdk: cache tracer configs in Tracer

[xrmx]

Description

Instead of creating the TracerConfig at each start_span call, just compute it on change. This changes an internal interface. This also introduces a change in behavior where only a tracer for the same instrumentation scope will be created and then cached.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[xrmx]

Benchmarks

-------------------------------------------------------------------------------------------------------- benchmark: 6 tests -------------------------------------------------------------------------------------------------------
Name (time in us)                                                 Min                 Max               Mean            StdDev             Median               IQR            Outliers  OPS (Kops/s)            Rounds  Iterations
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
test_simple_start_span_with_tracer_configurator_rules[None]     12.7530 (1.0)      39.7900 (1.53)     14.0253 (1.0)      0.9216 (1.46)     13.8770 (1.0)      0.7010 (1.17)      744;279       71.3000 (1.0)        8740           1
test_simple_start_span_with_tracer_configurator_rules[10]       12.8790 (1.01)     25.9930 (1.0)      14.2303 (1.01)     0.6878 (1.09)     14.1430 (1.02)     0.5973 (1.0)        374;75       70.2724 (0.99)       2909           1
test_simple_start_span_with_tracer_configurator_rules[1]        13.0920 (1.03)     28.6730 (1.10)     14.3815 (1.03)     0.6356 (1.01)     14.3170 (1.03)     0.6070 (1.02)     1181;152       69.5339 (0.98)       7239           1
test_simple_start_span_with_tracer_configurator_rules[0]        13.1550 (1.03)     30.4540 (1.17)     14.3915 (1.03)     0.6302 (1.0)      14.3320 (1.03)     0.6125 (1.03)     2882;316       69.4855 (0.97)      17352           1
test_simple_start_span_with_tracer_configurator_rules[50]       13.2760 (1.04)     27.8670 (1.07)     14.3546 (1.02)     0.8041 (1.28)     14.2400 (1.03)     0.6080 (1.02)        49;18       69.6643 (0.98)        727           1

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

after

-------------------------------------------------------------------------------------------------------- benchmark: 6 tests -------------------------------------------------------------------------------------------------------
Name (time in us)                                                 Min                 Max               Mean            StdDev             Median               IQR            Outliers  OPS (Kops/s)            Rounds  Iterations
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
test_simple_start_span_with_tracer_configurator_rules[0]      12.7130 (1.0)       34.4780 (1.0)      13.9008 (1.0)      0.6829 (1.0)      13.8050 (1.0)      0.5950 (1.14)     1285;287       71.9383 (1.0)        9127           1
test_simple_start_span_with_tracer_configurator_rules[50]     12.8570 (1.01)      85.8870 (2.49)     14.1029 (1.01)     1.0369 (1.52)     13.9990 (1.01)     0.5490 (1.05)      429;429       70.9077 (0.99)      14893           1
test_simple_start_span_with_tracer_configurator_rules[10]     12.8640 (1.01)      57.6480 (1.67)     14.0218 (1.01)     1.1011 (1.61)     13.9040 (1.01)     0.5220 (1.0)       459;583       71.3176 (0.99)      20711           1
test_simple_start_span_with_tracer_configurator_rules[1]      12.9070 (1.02)     186.0220 (5.40)     14.4462 (1.04)     2.6857 (3.93)     14.0930 (1.02)     0.6400 (1.23)     593;1007       69.2222 (0.96)      19222           1
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

[pmcollins]

Looks like a positive change overall, thanks for doing this.

[pmcollins]

LGTM, thanks

[lzchen]

Would returning a cached Tracer instead of a new instance be considered breaking in anyway (even though Tracers don't really have state)?

[lzchen]

Oh just saw your comment here. I guess this is ok?

[xrmx]

I won't bet on not having any downstream users with unexpected assumptions 😅 Anyway I think this is a positive change on its own since we are now removing an unbounded way to allocate objects.