Databases & queries
Data Vault
Where data lives, why it disagrees with itself, and how queries actually run.
The database is the part of your stack that survives the longest. Frameworks rotate; schemas accumulate. These activities make the mechanics of queries, indexes, transactions, and replication visible — so when a dashboard hits 8 seconds in production at the size where it ran in 80 milliseconds in dev, you can read the explain plan and know which bug you are looking at.
Database performance · ORM trapsN+1 Query Problem
Side-by-side: loop over users and fetch their posts one-at-a-time vs one IN-clause query. Watch query count and elapsed time fan out as users grow. The most common backend performance bug in the world, made impossible to miss.
Teaches: Phase 4 · Backend Engineering