Technologies/Express/express.eventloop.lag
ExpressExpressMetric

express.eventloop.lag

Event loop lag
Dimensions:None
Available on:PrometheusPrometheus (1)
Interface Metrics (1)
PrometheusPrometheus
Lag of event loop in seconds, indicating how long tasks are waiting in the event queue
Dimensions:None
Sources
nodejs_eventloop_lag_secondsgithub.com

Technical Annotations (105)

Configuration Parameters (11)
prisma.transaction.timeoutrecommended: 5000
Default Prisma transaction timeout in milliseconds
trace.logs.limitrecommended: 25000
Maximum number of logs to display in trace view
THRESHOLD_NSrecommended: 100000000
100ms threshold in nanoseconds for event loop monitoring
alert.eventloop.lag.thresholdrecommended: 1000
Alert threshold in milliseconds for event loop lag
chunkSizerecommended: 10000
Process 10,000 iterations at a time when chunking heavy calculations
package-lock.jsonrecommended: properly locked versions
prevents version drift and ensures consistent dependency performance
UV_THREADPOOL_SIZErecommended: 8
Increase from default 4 for heavy I/O on multi-core systems
wsEnginerecommended: uWebSockets
Use C++-based uWebSockets engine instead of default Socket.IO engine
perMessageDeflaterecommended: true
Enable per-message compression to reduce bandwidth
--max-semi-space-sizerecommended: larger than 4MB default
Increase to reduce GC frequency and use available RAM
tcp_nodelayrecommended: true
Disable Nagle's algorithm to prevent packet batching in real-time apps
Error Signatures (3)
Transaction already closed: A query cannot be executed on an expired transactionexception
Invalid `prisma.taskAttempt.create()` invocation: Transaction API errorexception
fs.readFileSynclog pattern
CLI Commands (24)
ssh -L 9221:localhost:9229 user@hostdiagnostic
node --trace-sync-io app.jsdiagnostic
npx clinic doctor -- node app.jsdiagnostic
npm install -g 0xdiagnostic
0x app.jsdiagnostic
node --inspect your_app.jsdiagnostic
clinic doctor -- node your_app.jsdiagnostic
npm install event-loop-lagmonitoring
function processInChunks(data, chunkSize = 1000) { let index = 0; function nextChunk() { const end = Math.min(index + chunkSize, data.length); for (; index < end; index++) { processData(data[index]); } if (index < data.length) { setImmediate(nextChunk); } } nextChunk(); }remediation
const { Worker } = require('worker_threads'); function runWorker() { return new Promise((resolve, reject) => { const worker = new Worker('./heavy-task.js'); worker.on('message', resolve); worker.on('error', reject); worker.on('exit', code => { if (code !== 0) reject(new Error(`Worker stopped with exit code ${code}`)); }); }); }remediation
const fs = require('fs'); const readStream = fs.createReadStream('large-file.txt'); readStream.on('data', chunk => { console.log(`Received ${chunk.length} bytes`); });remediation
npm lsdiagnostic
npm auditdiagnostic
npm deduperemediation
clinic doctor -- node your-app.jsdiagnostic
const { monitorEventLoopDelay } = require('perf_hooks'); const h = monitorEventLoopDelay(); h.enable(); setInterval(() => { console.log(`Event Loop Lag: ${Math.round(h.mean / 1e6)} ms`); }, 1000);monitoring
node --inspect your-app.jsdiagnostic
clinic.jsdiagnostic
0xdiagnostic
clinic doctor - node main.jsdiagnostic
clinic flame — node main.jsdiagnostic
node --trace-event-categories v8,node,node.async_hooks,node.perfdiagnostic
clinic doctordiagnostic
--trace-gcmonitoring
Technical References (67)
PinocomponentWinstoncomponentPM2componentfs.readFileSynccomponentevent loopconceptcrypto.pbkdf2SynccomponentPrismacomponentO(n^2) complexityconceptBig O notationconceptZodcomponentBuffer.byteLengthcomponentstream-jsoncomponentContent-Lengthprotocolnode:async_hookscomponentOpenTelemetrycomponentprocess.hrtimecomponentV8 profilercomponentprocess.hrtime.bigint()componentWorker ThreadscomponentsetImmediateconceptworker_threadscomponentfs.readFilecomponentasync/awaitconceptN+1 queriesconceptconnection poolingconceptcluster modulecomponentsetTimeoutcomponentWorkercomponentstreamcomponentfs.createReadStreamcomponentbackpressureconceptdebounceconceptthrottleconceptWebSocketsprotocolmoment.jscomponentdate-fnscomponentdayjscomponentfast-json-stringifycomponentclinic.jscomponentclinic doctorcomponentperf_hookscomponentmonitorEventLoopDelaycomponent--inspectcomponentChrome DevToolscomponentheap snapshotsconceptcallback queuecomponentJavaScript threadcomponentCPU profilercomponentreplicacomponentsingle-threadedconceptdistributed tracingcomponentSSRconceptChild Processescomponentfs.readFileSync()componentgarbage collectionconceptfs.promisescomponentPromise.allcomponentp-limitcomponentprom-clientcomponentClinic.jscomponentsetImmediate()componentSocket.IO cluster adaptercomponentWebRTC data channelsprotocolPeerJScomponentSocket.IOcomponentuWebSocketscomponentNagle's algorithmprotocol
Related Insights (48)
Synchronous logging blocks event loop in productionwarning
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Live debugging with Inspector pauses event loop and halts trafficcritical
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Event loop lag exceeds 10-20ms thresholdwarning
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Synchronous file system calls block event loopwarning
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Synchronous operations block event loop and tank throughputcritical
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Legacy Node.js versions reduce event loop efficiencywarning
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Prisma transaction timeouts due to event loop blockingcritical
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Nested loop over large datasets blocks event loopcritical
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Large unpaginated datasets cause resource exhaustioncritical
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Synchronous JSON parsing causes event loop lagwarning
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Monitor event loop blocking with async_hooksinfo
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High event loop lag degrades API responsivenesswarning
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Synchronous CPU-bound operations block event loopcritical
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Synchronous file I/O blocks event loop in productioncritical
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Poorly optimized database queries delay callback executionwarning
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100% CPU utilization prevents event loop processingcritical
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Synchronous loops block event loop causing application unresponsivenesscritical
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CPU-intensive tasks starve event loop requiring worker threadswarning
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Large file processing causes memory exhaustion and event loop lagwarning
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Request floods from APIs or WebSockets overload serverwarning
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Heavy third-party dependencies bloat application and degrade performancewarning
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Event loop lag detection requires monitoring toolinginfo
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Memory leaks indirectly cause event loop lagwarning
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Event loop blocking causes request latency spikes under concurrent loadcritical
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Event loop 100% utilization causes request latency spikes and timeoutscritical
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Synchronous CPU-intensive operations block event loop and cause latencycritical
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Horizontal scaling mitigates event loop starvation when under-provisionedwarning
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Event loop blocking misdiagnosed as downstream service latencywarning
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Response timer includes event loop wait time in observed latencyinfo
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Callback queue flooding from high request volume causes event loop starvationwarning
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Synchronous middleware operations block event loop causing throughput degradationwarning
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CPU-intensive tasks block event loop causing request delayscritical
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Synchronous file system calls stall event loopcritical
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Memory leaks cause garbage collection pauses and event loop latencywarning
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Event loop lag indicates delayed task executionwarning
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Poorly written dependencies introduce blocking operationswarning
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Event loop congestion causes severe response time degradation at scalecritical
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Synchronous file I/O blocks event loopwarning
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Unbatched concurrent promises cause event loop delayswarning
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CPU-intensive operations block event loop for secondscritical
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Event loop blocking causes health check failures and pod restartscritical
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Event loop lag over 300ms causes API response time degradationcritical
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Single-threaded Node.js process saturates one core despite multi-core availabilitycritical
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High-frequency real-time broadcasts flood event loop with micro-taskswarning
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Socket.IO abstraction overhead reduces throughput under high loadwarning
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Small default semi-space heap size causes frequent GC pauseswarning
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Nagle's algorithm batches TCP packets causing latency spikeswarning
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Node.js struggles to use more than 50% of single CPU before event loop laginfo
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