10BC0 Fix adaptive metrics decay when provider metrics are not updated by SURYAS1306 · Pull Request #16048 · apache/dubbo · GitHub
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Fix adaptive metrics decay when provider metrics are not updated #16048

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Fix adaptive metrics decay when provider metrics are not updated #16048

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@SURYAS1306 SURYAS1306 commented Jan 25, 2026

What is the purpose of the change?

This PR fixes an issue in AdaptiveLoadBalance / AdaptiveMetrics where latency decay behaves incorrectly when provider metrics are not updated for a period of time.

Currently, when no new provider metrics arrive, getLoad() may repeatedly apply the penalty branch or aggressively right-shift lastLatency, which can result in stale or extreme values dominating EWMA. This makes adaptive load balancing unstable, especially in low-QPS or intermittent-update scenarios.

This PR ensures that latency decays safely and progressively instead of collapsing or being stuck at penalty values.

Fixes #15810

What is changed?

1. Improved decay logic in AdaptiveMetrics#getLoad()

  • Prevents lastLatency from collapsing to zero.
  • Ensures decay happens smoothly when provider metrics are not refreshed.
  • Avoids repeatedly applying the penalty path when timestamps are equal.

2. Added unit test

Added testAdaptiveMetricsDecayWithoutProviderUpdate

Verifies that when provider metrics are not updated:

  • latency decays over time
  • penalty value is not stuck
  • EWMA continues to evolve

Why is this needed?

Adaptive load balancing relies on EWMA latency to reflect recent performance trends.

Without this fix:

  • old latency values can dominate indefinitely
  • penalty values may be repeatedly re-applied
  • low-traffic services become unfairly weighted

This change makes adaptive load balancing more stable, realistic, and robust under real-world traffic patterns.

Verifying this change

  • Added new unit test covering the decay scenario
  • All tests pass locally:
mvn -pl dubbo-cluster -am test

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codecov-commenter commented Jan 25, 2026 •
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Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 60.73%. Comparing base (f5d6436) to head (2113910).

Files with missing lines Patch % Lines
...ain/java/org/apache/dubbo/rpc/AdaptiveMetrics.java 50.00% 0 Missing and 1 partial ⚠️
Additional details and impacted files 
@@             Coverage Diff              @@
##                3.3   #16048      +/-   ##
============================================
- Coverage     60.75%   60.73%   -0.03%     
+ Complexity    11757    11752       -5     
============================================
  Files          1952     1952              
  Lines         89012    89012              
  Branches      13421    13421              
============================================
- Hits          54079    54059      -20     
- Misses        29367    29382      +15     
- Partials       5566     5571       +5
Flag Coverage Δ
integration-tests-java21 32.19% <0.00%> (+0.01%) ⬆️
integration-tests-java8 32.32% <0.00%> (-0.02%) ⬇️
samples-tests-java21 32.06% <0.00%> (-0.06%) ⬇️
samples-tests-java8 29.71% <0.00%> (-0.01%) ⬇️
unit-tests-java11 59.01% <50.00%> (-0.01%) ⬇️
unit-tests-java17 58.52% <50.00%> (+0.01%) ⬆️
unit-tests-java21 58.51% <50.00%> (-0.02%) ⬇️
unit-tests-java25 58.46% <50.00%> (-0.02%) ⬇️
unit-tests-java8 59.01% <50.00%> (-0.01%) ⬇️

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@SURYAS1306
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SURYAS1306 commented Jan 25, 2026

Hi maintainers,

This PR fixes the adaptive metrics decay issue when provider metrics are not updated and adds a unit test covering the scenario.

All checks are green. I’d really appreciate your review when you have time.

Thanks!

@SURYAS1306 SURYAS1306 mentioned this pull request Jan 25, 2026
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@zrlw
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zrlw commented Jan 27, 2026

you'd better add a comparison test to ensure applying this PR also does well under high QPS circumstance.

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SURYAS1306 commented Jan 27, 2026

Hi @zrlw , thanks for the suggestion.
That makes sense. I’ll add a comparison test to cover high QPS scenarios and update the PR soon

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SURYAS1306 commented Jan 27, 2026

Hi @zrlw , thanks for the suggestion.
I’ve added a high frequency style test to cover the adaptive metrics decay behavior and verified it by running the dubbo-cluster module tests locally.
All tests are passing now. Appreciate it if you could take another look.


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zrlw approved these changes Jan 28, 2026
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LGTM

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[BUG] Questions about Dubbo Adaptive Load Balance

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