[feat][broker] PIP-264: Enable OpenTelemetry reusable data memory mode

[dragosvictor]

PIP: https://github.com/apache/pulsar/blob/master/pip/pip-264.md

Motivation

The recently added OpenTelemetry 'reusable data' memory mode allows the OpenTelemetry SDK to reduce the number of memory allocations in between collector runs, at the expense of parallel collection. This is a fair compromise given Pulsar's use-case, and it promises to significantly improve the performance of the metric pipeline.

Modifications

Enables, by default, the OpenTelemetry 'reusable data' export mode. This can be overridden by the user at runtime via Java system property otel.java.experimental.exporter.memory_mode or environment variable OTEL_JAVA_EXPERIMENTAL_EXPORTER_MEMORY_MODE. See https://opentelemetry.io/docs/languages/java/configuration/#exporters for a few more details on the config.

Verifying this change

• Make sure that the change passes the CI checks.

This change is already covered by existing tests, such as:

• Integration test org.apache.pulsar.tests.integration.metrics.OpenTelemetrySanityTest

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations: As described above
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: dragosvictor#32

[lhotari]

LGTM