[dynamic control] only change the sampling rate if it has changed value

[jackshirazi]

Description:

The policy aggregator spec doesn't require already applied policy changes to be eliminated, it delegates that optimization to the implementation. I've added the optimization that if there is no effective change to the sampling rate, then no actual change is applied

Existing Issue(s):

#2868

Testing:

added

Documentation:

n/a

Outstanding items:

#2868

[Copilot]

Pull request overview

Optimizes the dynamic-control trace sampling policy application path by avoiding reapplying an equivalent sampling probability, reducing unnecessary sampler churn and log noise when policy updates repeat the same effective value.

Changes:

• Update TraceSamplingRatePolicyImplementer to apply sampling probability changes via DelegatingSampler.setSamplingProbability(...) and only log when an effective change occurs.
• Add probability tracking to DelegatingSampler to atomically skip repeated equivalent probability updates.
• Add a unit test to verify that repeated equivalent probability updates do not cause repeated delegate changes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRatePolicyImplementer.java	Applies sampling probability updates via a helper that only logs when the delegate actually changes.
dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/DelegatingSampler.java	Tracks last-applied probability and adds setSamplingProbability to skip equivalent updates.
dynamic-control/src/test/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRatePolicyImplementerTest.java	Adds coverage ensuring repeated equivalent probability updates only apply once.