How to log ALL PostgreSQL SQL happening

When you're using PostgreSQL for local development it's sometimes important to get an insight into ALL SQL that happens on the PostgreSQL server. Especially if you're trying to debug all the transaction action too.

To do this on OSX where you have PostgreSQL installed with Homebrew you have to do the following:

1. Locate the right postgresql.conf file. On my computer this is in /opt/boxen/homebrew/var/postgres/ but that might vary depending on how you set up Homebrew. Another easier way is to just start psql and ask there:

$ psql
psql (9.4.0)
Type "help" for help.

peterbe=# show config_file;
                   config_file
--------------------------------------------------
 /opt/boxen/homebrew/var/postgres/postgresql.conf
(1 row)

peterbe=#

Open that file in your favorite editor.

2. Look for a line that looks like this:

#log_statement = 'all'                   # none, ddl, mod, all

Uncomment that line.

3. Now if you can't remember how to restart PostgreSQL on your system you can ask brew:

$ brew info postgresql

Towards the end you'll see some files that look something like this:

$ launchctl unload ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
$ launchctl load ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

4. To locate where PostgreSQL dumps all logging, you have to look to how Homebrew set it up. You can do that by opening ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist. You'll find something like this:

<key>StandardErrorPath</key>
  <string>/opt/boxen/homebrew/var/postgres/server.log</string>

That's it. You can now see all SQL going on by running:

$ tail -f /opt/boxen/homebrew/var/postgres/server.log

Remember to reverse this config change when you're done debugging because that server.log file can quickly grow to an insane size since it's probably not log rotated.

Happy SQL debuggin'!

UPDATE Dec 2018

Another way to use Homebrew to restart PostgreSQL is with the command:

$ brew services restart postgresql

UPDATE Apr 2025

Use pg_stat_statements instead.

Great intro here: "Query Optimization in Postgres with pg_stat_statements".