Prepared transactions are disabled in PostgreSQL by default, since the parameter max_prepared_transactions has the default value 0. You don’t need prepared transactions in most cases. However, they can cause nasty problems, so I think that everybody who runs a PostgreSQL database should understand them. To illustrate these problems, I’ll show you how to use prepared […]

The ability to run transactions is the core of every modern relational database system. The idea behind a transaction is to allow users to control the way data is written to PostgreSQL. However, a transaction is not only about writing – it is also important to understand the implications on reading data for whatever purpose […]

If you happen to be an SQL developer, you will know that joins are really at the core of the language. Joins come in various flavors: Inner joins, left joins, full joins, natural joins, self joins, semi-joins, lateral joins, and so on. However, one of the most important distinctions is the difference between implicit and […]

Machine Learning in 10 Lines Every person that reads newspapers, magazines or any other media of general interest has at least a basic idea of what Machine Learning is. And this is not only a fashion, Machine Learning is already part of our everyday life and will be much more in the future: from personalized […]

  Since I only recently learned about the concept of “killed index tuples”, I thought there might be some others who are not yet familiar with this interesting PostgreSQL concept. This may give you an explanation the next time you encounter wildly varying execution times for the same execution plan of the same PostgreSQL query. […]

  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 […]

After you ANALYZE a PostgreSQL table to collect value distribution statistics, you will find the gathered statistics for each column in the pg_stats system view. This article will explain the meaning of the correlation column and its impact on index scans. Physical vs. logical ordering Most common PostgreSQL data types have an ordering: they support […]

PostgreSQL will shortly be released and it is therefore time to take a look at one of the most important new features provided by PostgreSQL 11: The ability to create indexes in parallel. For many years various commercial database vendors have already offered this feature and we are glad that PostgreSQL has become part of […]

Many of you out there using PostgreSQL streaming replication might wonder what this hot_standby_feedback parameter in postgresql.conf really does. Support customers keep asking this question so it might be useful to share this knowledge with a broader audience of PostgreSQL users out there. What VACUUM does in PostgreSQL VACUUM is an essential command in PostgreSQL […]

Sorting is a very important aspect of PostgreSQL performance tuning. However, tuning sorts is often misunderstood or simply overlooked by many people. So I decided to come up with a PostgreSQL blog showing, how sorts can be tuned in PostgreSQL. Creating sample data To show how sorting works, I created a couple of million rows […]

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 weakspots is therefore exactly what this post is all about. There are many ways to approach performance problems. However, […]

  Inspired by my co-worker’s recent blog post, I decided to revisit the old question of rules vs. triggers and run a little benchmark to see which one does better. About rules While triggers are well known to most application developers and database administrators, rules are less well known. The full name “query rewrite rule” […]