Edge-rendered HTML: TTFB 90ms but LCP +400ms

Edge-rendered HTML: TTFB 90ms but LCP +400ms
Moving SSR to the edge cut TTFB (time to first byte) but the trade wasn't free.
— TTFB 230ms -> 90ms (closer to user, no origin hop)
— But the edge worker fetched data from a single-region database: 280ms added before HTML streamed
— Net document complete was slower until we cached the data layer at the edge too
— After edge KV cache: full LCP 2.1s -> 1.4s
TTFB is a vanity metric if downstream fetches block the body.
Takeaway: TTFB 90ms only helps if the data is also at the edge.