Issue
sql_error_code = 00000 LOG: checkpoint starting: time is appearing in the logs for professional tier Heroku Postgres databases.
Resolution
This can be a source of confusion, but sql_error_code = 00000 LOG actually translates to "No error here".
The checkpoint log is part of the automatic WAL archiving activity that allows us to protect your database from catastrophic failures and is used in continuous protection and features like database forks and followers.