Technologies/Express/express.eventloop.lag.p99
ExpressExpressMetric

express.eventloop.lag.p99

99th percentile event loop lag
Dimensions:None
Available on:PrometheusPrometheus (1)
Interface Metrics (1)
PrometheusPrometheus
99th percentile of event loop lag in seconds
Dimensions:None
Sources
nodejs_eventloop_lag_p99_secondsgithub.com

Technical Annotations (27)

Configuration Parameters (3)
thresholdrecommended: 100
Event loop delay threshold in ms for warning alerts
resolutionrecommended: 10
Resolution for monitorEventLoopDelay histogram in ms
UV_THREADPOOL_SIZErecommended: 8
Increase from default 4 for heavy I/O on multi-core systems
CLI Commands (8)
node --trace-sync-io app.jsdiagnostic
node --inspect your_app.jsdiagnostic
clinic doctor -- node your_app.jsdiagnostic
npm install event-loop-lagmonitoring
clinic.jsdiagnostic
0xdiagnostic
node --inspect app.jsdiagnostic
node --trace-event-categories v8,node,node.async_hooks,node.perfdiagnostic
Technical References (16)
PM2componentevent loopconceptV8 profilercomponentprocess.hrtime.bigint()componentperf_hookscomponentmonitorEventLoopDelaycomponentworker_threadscomponentPiscinacomponentchild_processcomponentdebugcomponentPinocomponentTTFBconceptWorker ThreadscomponentChild Processescomponentblocked-atcomponentsetImmediate()component
Related Insights (16)
Event loop lag exceeds 10-20ms thresholdwarning
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Legacy Node.js versions reduce event loop efficiencywarning
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High event loop lag degrades API responsivenesswarning
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Event loop blocking causes complete application unresponsivenesscritical
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Event loop delay exceeding 100ms indicates blockingwarning
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Event loop blocking causes request latency spikes under concurrent loadcritical
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High p99 latency from event loop blocking patternswarning
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CPU-intensive operations block main event loop threadwarning
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Synchronous middleware operations block event loop causing throughput degradationwarning
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Synchronous console.log blocks production app on file/terminal outputwarning
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Event-loop stalls invisible without direct lag measurementcritical
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Event-loop stalls cause timeouts without error rate increasecritical
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CPU-intensive tasks block event loop causing request delayscritical
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Event loop lag indicates delayed task executionwarning
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Event loop lag exceeding 50ms indicates blocking operationswarning
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Event loop lag over 300ms causes API response time degradationcritical
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