23 lines
1.0 KiB
Markdown
23 lines
1.0 KiB
Markdown
---
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id: function-duration-io-and-after
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title: Function duration, I/O, and post-response work
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status: active
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candidateKinds: ["slow_route"]
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frameworks: ["next@>=15.0.0"]
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priority: 75
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citations: ["https://nextjs.org/docs/app/api-reference/functions/after", "vercel-react-best-practices:async-parallel", "vercel-react-best-practices:server-after-nonblocking"]
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maxBriefChars: 850
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---
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## Investigation Brief
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When wall-clock latency is much higher than CPU time, check critical-path awaits before blaming rendering or compute.
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## Evidence To Check
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Compare `cpu.p95`, `ttfb.p95`, and `latency.p95`. In source, separate dependent awaits from independent awaits, and identify analytics, logging, or notification work that can run after the response.
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## Do Not Recommend When
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Do not wrap dependent operations in `Promise.all`. Do not replace `Promise.allSettled` when partial failure handling is intentional.
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## Verification
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Name the awaits that can move, the work that can run post-response, and the observed CPU-vs-wall-clock gap.
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