CDN edge cache vs origin cache: TTFB math

CDN edge cache vs origin cache: TTFB math
Both cut TTFB. They cut different parts of it.
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Origin cache (Redis/page cache): skips DB + render. TTFB at origin ~600ms -> ~80ms. But the byte still crosses the ocean.
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CDN edge cache: serves from the nearest POP. Removes ~100-250ms of RTT for distant users.
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Stacked: edge HIT ~20-40ms TTFB globally; edge MISS falls back to your cached origin.
For a US origin and EU users, CDN alone removes the latency origin cache cannot.
Takeaway: edge HIT TTFB ~30ms vs cached-origin ~80ms + 150ms RTT.