Chung-En Lee created HDDS-15969:
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Summary: Prioritize Ratis Streaming capable DataNodes during
Pipeline creation with graceful fallback
Key: HDDS-15969
URL: https://issues.apache.org/jira/browse/HDDS-15969
Project: Apache Ozone
Issue Type: Improvement
Reporter: Chung-En Lee
During rolling upgrades or in heterogeneous clusters, random node selection
makes forming a 100% Ratis Streaming pipeline rare (e.g., (1/2)^3 = 12.5%
chance when 50% nodes support it), leading to frequent client fallbacks.
To maximize streaming pipeline creation without sacrificing availability, we
introduce a *two-phase node selection* strategy for {{{}THREE{}}}-factor
pipelines:
# *Strict Phase:* Exclude nodes lacking Ratis Streaming support (along with
over-utilized nodes) and attempt allocation.
# *Fallback Phase:* If allocation fails due to insufficient streaming nodes,
fall back to standard allocation with relaxed capability checks.
This prioritizes Ratis Streaming nodes when available while ensuring full
cluster fallback resilience.
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