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https://issues.apache.org/jira/browse/SOLR-18284?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18091657#comment-18091657
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ASF subversion and git services commented on SOLR-18284:
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Commit 636880bbf883e01039c6cff831b0ec02a4566fe5 in solr's branch
refs/heads/branch_9x from Mark Robert Miller
[ https://gitbox.apache.org/repos/asf?p=solr.git;h=636880bbf88 ]
SOLR-18284: Load-average and memory circuit breakers no longer stampede or trip
on transient pre-GC heap peaks (#4550)
> Fix load-average and memory circuit breakers
> --------------------------------------------
>
> Key: SOLR-18284
> URL: https://issues.apache.org/jira/browse/SOLR-18284
> Project: Solr
> Issue Type: Bug
> Reporter: Mark Robert Miller
> Priority: Major
> Labels: pull-request-available
> Time Spent: 6h 10m
> Remaining Estimate: 0h
>
> 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.
> * I extracted these from the experimental circuit breaker overhaul PR.
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