This post shows how to optimize a slow query that came out of the Reproducible Builds project. The Reproducible Builds initiative aims to make software compilation entirely deterministic, with no variation in the output when the build is run again. This makes software supply chain attacks much harder, but has also advantages for software quality […]

© Laurenz Albe 2023 SQL allows you to use subqueries almost anywhere where you could have a table or column name. All you have to do is surround the query with parentheses, like (SELECT …), and you can use it in arbitrary expressions. This makes SQL a powerful language – and one that can be […]

© Laurenz Albe 2023 PostgreSQL uses shared memory for data shared between processes. With the exception of the dynamic shared memory segments used for exchanging data between parallel workers, the server allocates shared memory with a fixed size when it starts. But each PostgreSQL backend process also has to manage private memory to process SQL […]

© Laurenz Albe 2023 Different from many other database systems, PostgreSQL does not support query hints. That makes it difficult to force the hand of the query planner when it comes to a certain join order that you know to be good. This article explains how you can influence execution plans in PostgreSQL. Why no […]

Rewriting OR is not always the best solution © Laurenz Albe 2022 In my article that reviles OR, I showed how in certain cases, it is possible to rewrite OR in a WHERE condition to a longer query with UNION that can perform much better (the “ugly” OR). Now people have asked me repeatedly why […]

Just like any advanced relational database, PostgreSQL uses a cost-based query optimizer that tries to turn your SQL queries into something efficient that executes in as little time as possible. For many people, the workings of the optimizer itself remain a mystery, so we have decided to give users some insight into what is really […]

PostgreSQL query optimization with CREATE STATISTICS is an important topic. Usually, the PostgreSQL optimizer (query planner) does an excellent job. This is not only true for OLTP but also for data warehousing. However, in some cases the optimizer simply lacks the information to do its job properly. One of these situations has to do with […]

Our PostgreSQL 24×7 support team recently received a request from one of our customers who was facing a performance problem. The solution to the problem could be found in the way PostgreSQL handles query optimization (specifically, statistics). So I thought it would be nice to share some of this knowledge with my beloved readers. The […]

© Laurenz Albe 2020 (Updated 2023-02-24) There are three join strategies in PostgreSQL that work quite differently. If PostgreSQL chooses the wrong strategy, query performance can suffer a lot. This article explains the join strategies, how you can support them with indexes, what can go wrong with them and how you can tune your joins […]

By Kaarel Moppel – UPDATED by Laurenz Albe 06.07.2023 – See what progress has been made What are PostgreSQL’s weaknesses? How can PostgreSQL be improved? Usually, in this blog I write about various fun topics around PostgreSQL – like perhaps new cool features, some tricky configuration parameters, performance of particular features or on some “life […]

PostgreSQL 12 is just around the corner and therefore we already want to present some of the new features we like. One important new feature gives users and devops the chance to control the behavior of the PostgreSQL optimizer. Prepared plans are always a major concern (especially people moving from Oracle seem to be most […]

  PostgreSQL commit 74dfe58a5927b22c744b29534e67bfdd203ac028 has added “support functions”. This exciting new functionality that allows the optimizer some insight into functions. This article will discuss how this will improve query planning for PostgreSQL v12. If you are willing to write C code, you can also use this functionality for your own functions. Functions as “black boxes” […]