Triggers to enforce constraints
Sometimes you want to enforce a condition on a table that cannot be implemented by a constraint. In such a case it is tempting to use triggers instead. This article describes how to do this and what to watch out for. It will also familiarize you with the little-known PostgreSQL feature of “constraint triggers”. […]
DECLARE CURSOR in PostgreSQL or how to reduce memory consumption
Have you ever heard about cursors in PostgreSQL or in SQL in general? If not you should definitely read this article in depth and learn how to reduce memory consumption in PostgreSQL easily. Cursors have been around for many years and are in my judgement one of the most underappreciated feature of all times. Therefore […]
Secure PostgreSQL – a reminder on various attack surfaces
Needless to say, security is a topic that nobody in the wider IT industry can ignore nowadays, with a constant flow of reports on data breaches of various scales. Most of such cases don’t result from direct attacks against databases though, but more from targeting Application / API / Webserver problems as database servers are […]
count(*) made fast
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 […]
Speeding up GROUP BY in PostgreSQL
In SQL the GROUP BY clause groups records into summary rows and turns large amounts of data into a smaller set. GROUP BY returns one records for each group. While most people know how to use GROUP BY not many actually know how to squeeze the last couple of percentage points out of the query. […]
Foreign data wrapper for PostgreSQL: Performance Tuning
Foreign data wrappers have been around for quite a while and are one of the most widely used feature in PostgreSQL. People simply like foreign data wrappers and we can expect that the community will add even more features as we speak. As far as the postgres_fdw is concerned there are some hidden tuning options, […]
unaccent: Getting rid of umlauts, accents and special characters
Database people dealing with natural languages are all painfully aware of the fact that encodings, special characters, accents and alike are usually hard to deal with. This is especially true if you want to implement search in a user friendly way. Consider the following example in PostgreSQL: My name contains a couple of of super […]
“LOCK TABLE” can harm your database’s health
Many people know that explicit table locks with LOCK TABLE are bad style and usually a consequence of bad design. The main reason is that they hamper concurrency and hence performance. Through a recent support case I learned that there are even worse effects of explicit table locks. Table locks Before an SQL statement […]
Choose plpgsql variable names wisely
Pavel Stehule recently wrote the post “Don’t use SQL keywords as PLpgSQL variable names” describing the situation when internal stored routine variable names match PostgreSQL keywords. But the problem is not only in keywords. Consider: Output: OK, at least we have no hidden error like in Pavel’s case. Let’s try to fix it specifying an […]
“Exclusive backup” method is deprecated – what now?
The “exclusive backup” method of calling pg_start_backup(‘label’) before backup and pg_stop_backup() afterwards is scheduled for removal in the future. This article describes the problems with the old method and discusses the options for those who still use this backup method. The “exclusive” backup method Before pg_basebackup was invented, there was only one online file-system […]
Looking at MySQL 8 with PostgreSQL goggles on
First off – not trying to kindle any flame wars here, just trying to broaden my (your) horizons a bit, gather some ideas (maybe I’m missing out on something cool, it’s the most used Open Source RDBMS after all) and to somewhat compare the two despite being a difficult thing to do correctly / objectively. […]
Implementing “AS OF”-queries in PostgreSQL
Over the years many people have asked for “timetravel” or “AS OF”-queries in PostgreSQL. Oracle has provided this kind of functionality for quite some time already. However, in the PostgreSQL world “AS OF timestamp” is not directly available. The question now is: How can we implement this vital functionality in user land and mimic Oracle […]