Day: February 20, 2026

Radim Marek takes us through the structure of a page:

If you read previous post about buffers, you already know PostgreSQL might not necessarily care about your rows. You might be inserting a user profile, or retrieving payment details, but all that Postgres works with are blocks of data. 8KB blocks, to be precise. You want to retrieve one tiny row? PostgreSQL hauls an entire 8,192-byte page off the disk just to give it to you. You update a single boolean flag? Same thing. The 8KB page is THE atomic unit of I/O.

But knowing those pages exist isn’t enough. To understand why the database behaves the way it does, you need to understand how it works. Every time you execute INSERT, PostgreSQL needs to figure out how to fit it into one of those 8,192-byte pages.

It is a little wild how three of the largest relational database systems use 8KB pages. I know that, on the SQL Server side, they’ve experimented with different page sizes internally and have repeatedly said that, even recently (the last time I heard this was maybe about 3 years ago at a SQL Saturday), there just isn’t a benefit from moving away from 8KB. But what’s in those 8KB differ, and Radim goes into details on what’s in PostgreSQL.

Paul Randal re-continues a series:

In the first part of this series I introduced basic terminology around logging so I recommend you read that before continuing with this post. Everything else I’ll cover in the series requires knowing some of the architecture of the transaction log, so that’s what I’m going to discuss this time. Even if you’re not going to follow the series, some of the concepts I’m going to explain below are worth knowing for everyday tasks that DBAs handle in production.

Note: as I progress through this series and talk about aspects of the log, there are often little edge-cases or weird behaviors in niche circumstances that have been added or changed over the years. I’ll ignore those unless I specifically want to call them out, otherwise the posts would be riddled with rat-holes and mazes of twisty-turny little passages (yes, I loved ’80s text-based adventure games 🙂 that would distract from the main things to learn about in each post.

Click through for a primer on virtual log files, log blocks, and log sequence numbers.