SOLR-18284: Load-average and memory circuit breakers no longer stampede or trip on transient pre-GC heap peaks#4549
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markrmiller merged 1 commit intoJun 25, 2026
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…de or trip on transient pre-GC heap peaks Load-average and memory circuit breakers were doing more harm than good under high concurrency. LoadAverageCircuitBreaker called OperatingSystemMXBean.getSystemLoadAverage() on every request. The OS load average is a one-minute moving average, so re-polling it per-request is wasted work - and when many requests arrived concurrently, the syscall stampede hammered the CPU, which is the condition this breaker exists to prevent rather than cause. MemoryCircuitBreaker sampled MemoryMXBean.getHeapMemoryUsage().getUsed() on a 30-second moving average. With a generational collector that signal climbs toward max between collections during normal operation; the breaker would trip on transient pre-GC peaks that GC was about to reclaim.
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Load-average and memory circuit breakers were doing more harm than good under high concurrency.
LoadAverageCircuitBreaker called OperatingSystemMXBean.getSystemLoadAverage() on every request. The OS load average is a one-minute moving average, so re-polling it per-request is wasted work - and when many requests arrived concurrently, the syscall stampede hammered the CPU, which is the condition this breaker exists to prevent rather than cause.
MemoryCircuitBreaker sampled MemoryMXBean.getHeapMemoryUsage().getUsed() on a 30-second moving average. With a generational collector that signal climbs toward max between collections during normal operation; the breaker would trip on transient pre-GC peaks that GC was about to reclaim.
https://issues.apache.org/jira/browse/SOLR-18284