[unchar1]

We did an A/B test of an old SPA app, and a modern re-write using SSR and server-rendered pages.

By every performance metric, the new app was faster.

But we kept getting user feedback that the new site was "clunky" and "slow", even though we saw that the p90 was much lower on the new site. Most of our users asked us to enable a toggle to let them go back to the old "fast" site.

I'm not sure if this is a universal experience, but I think a lot of other sites that tried the CSR -> SSR move had similar experiences. It's just harder to talk about, since it goes against the usual narrative.

[bob1029]

SSR can feel worse than SPA if you don't get the end-to-end latency under a certain threshold. If your SSR pages are taking upward of 100ms to render on average, it's going to start to feel like shit once you factor in the network latency.

My design goal for modern SSR pages is 500 microseconds render time on the server. A modern CPU can crank through several gigabytes of UTF8 text per second. There really isn't any excuse from a technology perspective. SSR pages being perceived as clunky & slow boils down to a skill / people / organizational problem. The computers and associated networks can definitely do it well.

[nfw2]

Every single action should have no perceivable latency between the action and the feedback that the action was received. You can implement that with SSR but it is clunky and also requires a lot of JS generally.

[nfw2]

I am curious to identify what your users are perceiving that isn't be being captured by your metric. If it is accurate and not just rhetoric that MOST of your users are asking for a rollback for purely performance reasons, that is a very extreme outcome.

Are your p90 metrics testing:

- navigation after first load?

- users who are going to the app after it is cached on their browser?

Are your actions going through server actions or rest apis? Do you have metrics on those?