Performance
Memory Leaks: How They Happen and How to Find Them
What memory leaks actually are in garbage-collected languages, the common patterns that cause them, and how to use heap profiling to track down and fix them.
Performance
Database Query Performance: EXPLAIN and What It Tells You
How to read a Postgres EXPLAIN ANALYZE output, what sequential scans and index scans mean, and how to identify and fix slow queries before they become incidents.
Performance
Profile First, Optimize Second
Why guessing at performance bottlenecks wastes time, and how to use profiling tools to find what actually needs fixing before you touch the code.
Performance
Caching Strategies: Where to Cache and What to Invalidate
Caches speed things up until they serve stale data. Understanding the tradeoffs at each caching layer - and how invalidation actually works - is what keeps them from becoming bugs.