Tag: optimizer
Rewrite OR to UNION in PostgreSQL queries
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 […]
How the PostgreSQL query optimizer works
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: CREATE STATISTICS – advanced query optimization
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 […]
PostgreSQL: ANALYZE and optimizer statistics
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 […]
Join strategies and performance in PostgreSQL
© Laurenz Albe 2020 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 for better […]
PostgreSQL v12 new feature: optimizer support for functions
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” […]
Join pruning – Cool stuff in PostgreSQL
The PostgreSQL optimizer is really a wonderful piece of software, which is capable of doing great things. One of those great things is so called “join pruning”. In case PostgreSQL is able to detect a join which is actually not needed for execution, it will automatically remove it from the plan. Removing joins from the […]