How to Fix an AI-Built App That Is Slow Under Real Load

What is actually happening

AI tools optimize for code that works, not code that scales. The default patterns generate are fine for 10 users and fall apart at 100. The performance issues compound: a slow query causes a slow page, which keeps the user's browser open longer, which holds open more database connections, which makes the next query slower.

The fix, in order

Try these in sequence. Most apps are fixed by the first or second step.

1. 1

   Find and add the missing database indexes

   In Supabase, go to Database then Query Performance. Look at the slowest queries. For each one, identify the columns in the WHERE clause and add an index. Run: CREATE INDEX idx_table_column ON public.table_name(column_name); This single step usually drops query times from seconds to milliseconds.

2. 2

   Stop fetching all the data when you only need some

   AI-generated code often does .select('*') on every query. Replace with .select('only,the,columns,you,need'). Also: if you are paginating, use .range(start, end) instead of fetching all rows and slicing in JavaScript.

3. 3

   Cache the things that do not change often

   If your app calls the same API route 100 times to get the same data, add caching. In Next.js, use 'export const revalidate = 60' on the route or fetch with { next: { revalidate: 60 } } to cache responses for 60 seconds. For static data, set revalidate = 3600 or longer.

4. 4

   Move work to the server where it belongs

   AI tools love client components because they are easier to scaffold. But anything that fetches data, does heavy computation, or queries a database should be a server component or server action. Look for 'use client' directives and move data-fetching logic out of them.

5. 5

   Run Lighthouse and fix the top three issues

   In Chrome DevTools, open the Lighthouse tab and run a Performance audit on a deployed page. Lighthouse gives you specific issues with specific fixes. Focus on the top three: usually they are unoptimized images, render-blocking JS, and bad LCP (largest contentful paint).

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