High Performance PostgreSQL for Rails

Logging Slow Queries

Earlier you saw how to log slow queries to the Rails log. In this section, let’s look at logging them in the postgresql.log.

Open up your postgresql.conf file. Set the following log_min_duration_statement value and save your changes. Reload the config file values by running pg_ctl reload. This assumes you’ve set the PGDATA environment variable (see ​Set PGDATA for pg_ctl​).

Start with a value of one second, with an entry like this:

sh/set_log_min_duration_statement.sh

log_min_duration_statement = 1000

After reloading, tail the PostgreSQL log file to see the output. From psql, run SELECT pg_sleep(1); to create a query that’s one second long and verify it’s logged. Refer to the pg_scripts repo^[177] administration directory ...