Query in PostgreSQL became slow and then got better on its own - why? I want to better understand how to debug and fix performance issues in PostgreSQL.

I have a query that usually costs 1 second to run. However, for some reason, it started taking 30 seconds to run for a period of time! After some minutes and some explain analyze invocations, it went back to normal. I didn't do anything to fix it, nor did I understand why it got better all of a sudden.

How do I debug a problem like this? What kind of logging and instrumentation should I have in place to understand what caused this and how to fix it?
It is a very broad question, even more so as you give absolutely no details about your setup and kind of database (volume, type of queries, active connections, size of RAM, dedicated server or not, etc.)

You can start by enabling PostgreSQL to log slow queries, see the log_min_duration_statement in the configuration. That will give you historical data that you would then be able to analyze and maybe correlate with other things (like from the list of @Vérace)

You will then have various tools to help, as described on https://wiki.postgresql.org/wiki/Logging_Difficult_Queries :


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