PostgreSQL

In the late 1970s, Jim Gray and his colleagues at IBM Research were working on transaction processing systems that needed to guarantee data integrity even when power failed mid-operation. His solution was elegant in its simplicity: never write data to the main store until you’ve first written it to a log. This principle, formalized in his 1981 paper “The Transaction Concept: Virtues and Limitations,” became known as Write-Ahead Logging, and decades later, it remains the foundation of every major database system. ...

In 2012, a team of database researchers published a paper that would reshape how engineers think about transaction isolation. The paper, titled “Serializable Snapshot Isolation in PostgreSQL,” described a subtle anomaly that had been hiding in plain sight for decades: two transactions could both execute correctly in isolation, yet produce an incorrect result when run concurrently. The anomaly wasn’t a dirty read or a phantom—it was something called write skew, and it exposed a fundamental truth about the ANSI SQL isolation levels: the names don’t always mean what developers think they mean. ...

The Oracle Real-World Performance group published a demonstration that should have changed how every developer thinks about connection pools. They took a system struggling with ~100ms average response times and reduced those times to ~2ms—a 50x improvement. They didn’t add hardware. They didn’t rewrite queries. They reduced the connection pool size from 2048 connections down to 96. Most developers configure connection pools based on intuition: more users means more connections, right? A typical production configuration sets the pool to 100, 200, or even 500 connections “just to be safe.” This intuition is precisely backwards. The correct question isn’t how to make your pool bigger—it’s how small you can make it while still handling your load. ...