React on Rails Performance Demo

Desktop reports use 50 ms artificial DB delay to emulate real-world load

This demo app is small and fast — under normal conditions all three rendering strategies score similarly on desktop. PageSpeed Insights does not throttle CPU or network on desktop, so it cannot surface the performance differences that matter in production. Adding ?delay=50 to every page injects a 50 ms sleep after each database query, simulating the heavier queries and higher latency of a real-world application. This makes the RSC streaming advantage clearly visible in Lighthouse scores. The 50 ms delay emulates typical database latency and API response times seen in production applications under load.

Metric Client SSR Δ
Performance score 97 96 -1%
First Contentful Paint 672 ms 626 ms -7%
Largest Contentful Paint 948 ms 847 ms -11%
Total Blocking Time ★ 20 ms 92 ms +372%
Cumulative Layout Shift 0.0 0.0 +0%
Speed Index 1.33 s 1.67 s +26%
Script Bootup 320 ms 354 ms +11%
Total Transfer 790 KB 790 KB +0%

★ Blocking Time has the biggest impact on Google's performance score (30%) — it measures how long users wait before they can tap, scroll, or type (LCP 25%, CLS 25%, FCP 10%, SI 10%).

Client Desktop · product-search_client-desktop
SSR Desktop · product-search_ssr-desktop