Latency numbers to know

Reading memory takes about 100 ns, an SSD read about 100 µs, a round trip in the same datacenter about 0.5 ms and across a continent 50 to 150 ms. These orders of magnitude decide where data must live.

Where it shows up in real systems

  • CDN

    Images, scripts, styles and videos are cached at the edge, so most requests never reach your servers. Longer TTLs raise the hit ratio but make content updates slower to appear; an origin shield collapses cache misses from all edges into one.

    In production: Amazon CloudFront, Cloudflare, Akamai, Fastly, Azure Front Door

  • Edge function

    Ideal for redirects, A/B tests, authentication checks and personalisation without a round trip to your region. Execution time and memory are tightly limited, and anything that needs your database still pays the trip back to it.

    In production: Cloudflare Workers, AWS Lambda@Edge, CloudFront Functions, Vercel Edge Functions, Fastly Compute

See it break, then fix it

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