© Laurenz Albe 2020 HOT updates are not a new feature. They were introduced by commit 282d2a03dd in 2007 and first appeared in PostgreSQL 8.3. But since HOT is not covered by the PostgreSQL documentation (although there is a README.HOT in the source tree), it is not as widely known as it should be: Hence […]

© 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 […]

© Laurenz Albe 2020 A while ago, I wrote about B-tree improvements in v12. PostgreSQL v13, which will come out later this year, will feature index entry deduplication as an even more impressive improvement. So I thought it was time for a follow-up. Deduplication for B-tree indexes If the indexed keys for different table rows […]

© Laurenz Albe 2020 A frequently asked question in this big data world is whether it is better to store binary data inside or outside of a PostgreSQL database. Also, since PostgreSQL has two ways of storing binary data, which one is better? I decided to benchmark the available options to have some data points […]

© Laurenz Albe 2020 Most people know that autovacuum is necessary to get rid of dead tuples. These dead tuples are a side effect of PostgreSQL’s MVCC implementation. So many people will be confused when they read that from PostgreSQL v13 on, commit b07642dbc adds support for autovacuuming insert-only tables (also known as “append-only tables”). […]

© Laurenz Albe 2020 In my daily work, I see many databases with a bad setting for max_connections. There is little advice out there for setting this parameter correctly, even though it is vital for the health of a database. So I decided to write up something. What is max_connections? According to the documentation, max_connections […]

© Laurenz Albe 2020   Recently, while troubleshooting PostgreSQL performance problems, I ran into problems with subtransactions twice. So I thought this was a nice topic for another blog post. What are subtransactions? Everybody knows database transactions. In PostgreSQL, which is operating in autocommit mode, you have to start a transaction that spans multiple statements […]

  With the latest major version freshly released, it’s again time to gauge its performance. I’ve already been doing this for years, and I have my scripts ready, so it’s not too much work for me – but rather, for the machines. The v12 release, as always, adds quite a lot of nice stuff. Some […]

  It is a frequent complaint that count(*) is so slow on PostgreSQL. In this article I want to explore the options you have get your result as fast as possible. Why is count(*) so slow? Most people have no trouble understanding that the following is slow: After all, it is a complicated query, and […]

  Foreign key constraints are an important tool to keep your database consistent while also documenting relationships between tables. A fact that is often ignored is that foreign keys need proper indexing to perform well. This article will explain that and show you how to search for missing indexes. Index at the target of a […]

When digging into PostgreSQL performance it is always good to know, which option one has to spot performance problems and to figure out, what is really going on on a server. Finding slow queries and performance weak spots is therefore exactly what this post is all about. There are many ways to approach performance problems. […]

  We all know that you have to pay a price for a new index you create — data modifying operations will become slower, and indexes use disk space. That’s why you try to have no more indexes than you actually need. But most people think that SELECT performance will never suffer from a new […]