Tag: statistics
Enabling and disabling autovacuum in PostgreSQL
Autovacuum has been part of PostgreSQL for a long time. But how does it really work? Can you simply turn it on and off? People keep asking us these questions about enabling and disabling autovacuum a lot. PostgreSQL relies on MVCC to handle concurrency in a multiuser environment. The problem which arises when handling concurrent […]
Estimating connection pool size with PostgreSQL database statistics
© Laurenz Albe 2021 PostgreSQL v14 has new connection statistics in pg_stat_database. In this article, I want to explore one application for them: estimating the correct size for a connection pool. New connection statistics in v14 Commit 960869da080 introduced some new statistics to pg_stat_database: session_time: total time spent by sessions in the database active_time: time […]
PostgreSQL: CREATE STATISTICS – advanced query optimization
PostgreSQL query optimization with CREATE STATISTICS is an important topic. Usually, the PostgreSQL optimizer (query planner) does an excellent job. This is not only true for OLTP but also for data warehousing. However, in some cases the optimizer simply lacks the information to do its job properly. One of these situations has to do with […]
PostgreSQL: ANALYZE and optimizer statistics
Our PostgreSQL 24×7 support team recently received a request from one of our customers who was facing a performance problem. The solution to the problem could be found in the way PostgreSQL handles query optimization (specifically, statistics). So I thought it would be nice to share some of this knowledge with my beloved readers. The […]
Correlation of PostgreSQL columns explained
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 […]
3 ways to detect slow queries in PostgreSQL
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 weak spots is therefore exactly what this post is all about. There are many ways to approach performance problems. […]