# Tail latency: why the slowest requests matter most

DevFeed: [Tail latency: why the slowest requests matter most](<https://devfeed.tech/articles/tail-latency-why-the-slowest-requests-matter-most-4852.md>)

Original publisher: [Read original article](<https://redis.io/blog/tail-latency-why-slowest-requests-matter-most/>)

Author: Jim Allen Wallace

Published: 2026-07-04T00:00:00Z

Content type: article

Language: en

Sources: [Redis Blog](<https://devfeed.tech/sources/redis-blog.md>)

Topics: [Latency](<https://devfeed.tech/topics/latency.md>), [Back end](<https://devfeed.tech/topics/backend.md>), [servers](<https://devfeed.tech/topics/servers.md>), [API](<https://devfeed.tech/topics/api.md>), [App](<https://devfeed.tech/topics/app.md>)

Tags: [app](<https://devfeed.tech/tags/app.md>), [architecture](<https://devfeed.tech/tags/architecture.md>), [article](<https://devfeed.tech/tags/article.md>), [backend](<https://devfeed.tech/tags/backend.md>), [latency](<https://devfeed.tech/tags/latency.md>), [performance](<https://devfeed.tech/tags/performance.md>), [responses](<https://devfeed.tech/tags/responses.md>), [server](<https://devfeed.tech/tags/server.md>), [tech-de](<https://devfeed.tech/tags/tech-de.md>)

## AI overview

Explains tail latency, the slowest requests hidden by averages, and why percentile measurements such as p95, p99, and p99.9 better reveal user-impacting performance problems. It also describes how fan-out across backend servers amplifies the effect of a single slow sub-response.

## Source excerpt

Tail latency is the handful of requests that take far longer than the rest, hiding inside an average that looks perfectly fine. Your dashboard shows a 50ms average, everyone seems happy, and then support tickets start piling up about the app feeling s...