TTFB p75 540ms -> 110ms via cache HIT ratio

TTFB p75 540ms -> 110ms via cache HIT ratio
TTFB (time to first byte) was dominated by origin round-trips, not server compute.
— CDN HIT ratio was 61%; the 39% MISS traffic dragged the p75 up
— Raised ratio to 94% by normalizing query strings and stripping tracking params before the cache key
— MISS TTFB stayed ~480ms; HIT TTFB was 40-90ms — the percentile moved because fewer requests fell into the slow bucket
Field data confirmed: p75 dropped but p95 only moved to 380ms (logged-in users bypass cache).
Takeaway: 94% HIT ratio = -430ms at p75, untouched at p95.