© 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 […]

SQL and PostgreSQL are perfect tools to analyze data. However, they can also be used to create sample data which has to possess certain statistical properties. One thing many people need quite often is a normal distribution. The main question therefore is: How can one create this kind of sample data? Tablefunc: Creating normal distributions […]

Is it Postgre, PostGreSQL, Postgres or PostgreSQL? We have all seen a couple of wrong ways to spell “PostgreSQL”. The question therefore is: How can one find data even if there are typos? In PostgreSQL there are various solutions to the problem. Depending on what kind of search you need you can choose between various […]

© 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 […]

GROUP BY is nothing new and is available in any relational database I am aware of. It is an integral part of SQL and PostgreSQL but what many people might not know is the fact that GROUP BY can do more than just group by simple fields. You can use expressions to group in an […]

© 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 […]

An introductory story (with some slight “drama” added for fun) from those good old days of on-site consulting 🙂 So…I’m at a client where the database is not behaving nicely among other things…what a crappy DB product indeed I hear, it gets cranky every morning although there should be a constant workload and is saturating […]

A lot has been written about effective_cache_size in postgresql.conf and about PostgreSQL performance in general. However, few people know what this famous parameter really does. Let me share some more insights. What the PostgreSQL optimizer does The idea behind SQL is actually quite simple: The end user sends a query and the optimizer is supposed […]

Recently I was asked if there’s a rule of thumb / best practice for setting the fillfactor in Postgres – and the only answer I could give was to decrease it “a bit” if you’re doing lots and lots of updates on some table. Good advice? Well it could be better of course – this […]

LIKE and ILIKE are two fundamental SQL features. People use those things all over the place in their application and therefore it makes sense to approach the topic from a performance point of view. What can PostgreSQL do to speed up those operations and what can be done in general to first understand the problem […]

After exactly half a year (seems to be a pattern already) since the last major release of pgwatch2 Open Source PostgreSQL monitoring tool, I’m glad to announce that another set of useful features and improvements have found their way into the pgwatch2 code repository! New version is incremented to v1.8.0 and content wise it’s mostly […]

SQL and especially PostgreSQL provide a nice set of general purpose data types you can use to model your data. However, what if you want to store fewer generic data? What if you want to have more advanced server side check constraints? The way to do that in SQL and in PostgreSQL in particular is […]