HOT updates in PostgreSQL for better performance
© 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 […]
Tuning PostgreSQL autovacuum
© Laurenz Albe 2020 In many PostgreSQL databases, you never have to think or worry about tuning autovacuum. It runs automatically in the background and cleans up without getting in your way. But sometimes the default configuration is not good enough, and you have to tune autovacuum to make it work properly. This article presents […]
Understanding recursive queries in PostgreSQL
© Laurenz Albe 2020 Many people consider recursive queries a difficult topic. Still, they enable you to do things that would otherwise be impossible in SQL. This articles gives a simple introduction with examples and shows the differences to Oracle’s implementation of recursive queries. Common table expressions (WITH clauses) A common table expression (CTE) can […]
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 […]
Deduplication in PostgreSQL v13 B-tree indexes
© 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 […]
Binary data performance in PostgreSQL
© 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 […]
PostgreSQL v13 new feature: tuning autovacuum on insert-only tables
© 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”). […]
Tuning max_connections in PostgreSQL
© 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 […]
Embedded SQL in C for PostgreSQL with ecpg
© Laurenz Albe 2020 Embedded SQL is by no means a new feature — in fact it is so old-fashioned that many people may not know about it at all. Still, it has lots of advantages for client code written in C. So I’d like to give a brief introduction and talk about its […]
Subtransactions and performance in PostgreSQL
© 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 […]
recovery.conf is gone in PostgreSQL v12
© Laurenz Albe 2019 The biggest change in PostgreSQL v12 from the viewpoint of backward compatibility is that recovery.conf has been absorbed into postgresql.conf. This article describes the changes and how you can adapt to them. Getting rid of recovery.conf Up to now, the presence of the file recovery.conf was the trigger for PostgreSQL to […]
B-tree index improvements in PostgreSQL v12
Image © Laurenz Albe 2019 If you thought that the B-tree index is a technology that was perfected in the 1980s, you are mostly right. But there is still room for improvement, so PostgreSQL v12 (in the tradition of v11) has added some new features in this field. Thanks, Peter Geoghegan! In this article, I […]