Issue
You have observed some SQL error codes (in the format of sql_error_code = XXXXX) emitted in the logs of Heroku Postgres, and are not sure what they mean.
Resolution
Postgres emits error codes for all operations, including successful operations, that follow the SQLSTATE conventions as part of the SQL standard.
The most common emitted error code is 00000, meaning "successful completion". This is equivalent to an INFO log level. Detailed information on all the error codes can be found here: https://www.postgresql.org/docs/current/static/errcodes-appendix.html