Add benchmark for log sdk

[jack-berg]

The typical usage for logs presents the opportunity for hotspots that don't exist in traces or metrics.

The main use case we want to support is writing log appenders, which bridge other log APIs / frameworks into opentelemetry. Its very typical for these frameworks to have the notion of named loggers, which maps nicely to OpenTelemetry instrumentation scope name. However, this requires that appender implementations obtain a Logger instance for each log record processed. Here's an example. Its not typical to obtain a new tracer or meter for each span / measurement, so optimizing this area has not been a priority.

This code path is currently suboptimal, particularly in terms of allocations, since it requires creating a new SdkLoggerBuilder, which creates a new InstrumentationScopeInfoBuilder and a new InstrumentationScopeInfo.

There are a couple of obvious ways to optimize this. This PR establishes a benchmark representative of the typical appender use case to evaluate potential performance improvements.

Baseline performance on my machine:

Benchmark                                                  Mode  Cnt     Score     Error   Units
LogsBenchmarks.emitSimpleLog                               avgt   10    35.035 ±   0.732   ns/op
LogsBenchmarks.emitSimpleLog:·gc.alloc.rate                avgt   10  2173.006 ±  43.649  MB/sec
LogsBenchmarks.emitSimpleLog:·gc.alloc.rate.norm           avgt   10   120.000 ±   0.001    B/op
LogsBenchmarks.emitSimpleLog:·gc.churn.G1_Eden_Space       avgt   10  2191.457 ± 429.679  MB/sec
LogsBenchmarks.emitSimpleLog:·gc.churn.G1_Eden_Space.norm  avgt   10   120.983 ±  23.200    B/op
LogsBenchmarks.emitSimpleLog:·gc.count                     avgt   10    37.000            counts
LogsBenchmarks.emitSimpleLog:·gc.time                      avgt   10    30.000                ms

[codecov]

Codecov Report

Base: 90.83% // Head: 90.83% // No change to project coverage 👍

Coverage data is based on head (f4d0f70) compared to base (21d5597).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
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  Coverage     90.83%   90.83%           
  Complexity     4857     4857           
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  Files           556      556           
  Lines         14475    14475           
  Branches       1410     1410           
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  Hits          13149    13149           
  Misses          908      908           
  Partials        418      418           

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[jkwatson]

Can you paste the current benchmark results into the PR description, so we have a historical record? Thanks!

[jack-berg]

Done!