https://lqo.net/tags/guides/ Recent content in Guides on lqo.net Hugo en-us Sun, 18 Oct 2026 00:00:00 +0000 https://lqo.net/what-is-a-learned-query-optimizer-why-postgresql-picks-slow-plans-and-how-to-steer-it/ Sun, 18 Oct 2026 00:00:00 +0000 https://lqo.net/what-is-a-learned-query-optimizer-why-postgresql-picks-slow-plans-and-how-to-steer-it/ <p>A query optimizer turns your SQL into a plan: which table to read first, which index to use, how to join one table to the next. A learned query optimizer is one that improves its choices from what actually happened when queries ran, instead of trusting its own predictions. The idea is older than it sounds, and it&rsquo;s finally practical.</p> <p>To see why it matters, look at how an ordinary optimizer goes wrong.</p>