PostgreSQL Server Log Configuration

Monitoring and Operations / Guide 40 of 47 / Intermediate

• OSUbuntu 26.04 LTS
• PostgreSQL18.6-0ubuntu0.26.04.1
• Host2 core / 4 GB, 400,000-row test table
• TimeAbout 18 min

log_connections became a list in PostgreSQL 18 - receipt, authentication, authorization. on is still accepted and means all of them. On 17 and earlier it is a plain boolean.

This guide includes

Use this when pg_current_logfile() returns NULL and there is still a log. This matters because the packaging does not use the logging collector - so what matters is the prefix, and the three things actually worth logging.

• finding the log the packaging really uses, with the collector switched off
• reading log_line_prefix, and what each escape in it means
• logging the statements slower than a threshold
• logging connections the PostgreSQL 18 way, and logging lock waits
• putting it back, and meeting a role that will not drop

Before you start

• Shell access as a user who can sudo -u postgres and read /var/log/postgresql/.

1. 1

   Find the log the packaging actually uses

2. 2

   Read the prefix

3. 3

   Log the slow statements

4. 4

   Log who connects, PostgreSQL 18 style

5. 5

   Log the lock waits

6. 6

   Put it back, and hit a role that will not drop

Official sources

• PostgreSQL 18 Documentation - The Statistics Collector
• PostgreSQL 18 Documentation - Viewing Locks
• PostgreSQL 18 Documentation - Explicit Locking
• PostgreSQL 18 Documentation - Error Reporting and Logging
• PostgreSQL 18 Documentation - Connections and Authentication
• PgBouncer Documentation