System Design - database
#01 Database
The Database Is the Bottleneck. Always. Premium
CPU is 10%. RAM is fine. But the DB has 8,000 connections and is sweating. One missing index and one N+1 query and the whole system chokes.
Read
#02 Schema Migration
The Migration That Broke Production Premium
ALTER TABLE on 400M rows. It locks. Everything downstream times out. You learn about online schema migration the hard way.
Read