Bug Hunt
How a Timezone Bug Silently Corrupted Three Months of Analytics
The dashboard looked right. The numbers were wrong by a few percent every day, and the reason was one implicit conversion in a reporting query.
Networking
Your Webhook Handler Will Be Called Twice; Plan For It
At-least-once delivery means duplicates are normal operation, not an edge case. Here is how to build a handler that survives them.
Databases
Your Cache Serves Stale Data and the Bug Is Invalidation
Reading from cache is easy. Knowing when to remove something is where the bugs live, and most of them are races.
PostgreSQL
The Database Migration That Locked the Table for Nine Minutes
Adding a column should be instant. Sometimes it is not, and the difference is worth knowing before you run it in production.
Databases
Finding the N+1 Queries You Do Not Know You Have
The code reads beautifully and issues four thousand queries. Here is how to detect them automatically instead of discovering them in production.
PostgreSQL
FATAL: sorry, too many clients already
Connection pooling explained through the failure it prevents, and why raising max_connections is usually the wrong fix.