Database Systems

PostgreSQL, MySQL, Redis, MongoDB, and the architecture decisions behind choosing the right database for the right job. Query optimization, replication, migrations, and the stuff nobody teaches you until something breaks.

Database Systems | banditz

How to Diagnose and Fix MySQL Replication Lag

Your replica is 300 seconds behind. Reads return stale data and users see ghost records. Here's how to find the cause and fix it without breaking replication.

Jan 7, 2026

MySQL SHOW REPLICA STATUS showing high Seconds_Behind_Master

Database Systems | banditz

How to Find and Fix Slow Queries in PostgreSQL — Read EXPLAIN ANALYZE Before You Add Random Indexes

Your API endpoint takes 4 seconds to respond. Your dashboard loads like it's 2003. Someone suggests "just add an index" without even looking at the query plan. Stop. The problem might not be a missing index at all — it could be stale statistics, a bad join order, an ORM generating garbage SQL.

Jan 1, 2026

PostgreSQL EXPLAIN ANALYZE output showing sequential scan bottleneck with actual time highlighted