PostgreSQL Appendix A. PostgreSQL Error Codes

https://www.postgresql.org/docs/current/errcodes-appendix.html

• FATAL 53300 remaining connection slots are reserved for non-replication superuser connections

See also

• FATAL
• PostgreSQL: psql, .psqlrc, .pgpass, $HOME/.pg service.conf, -U, -W, -d, meta-commands: \du, \dg, \ddp, \dp, \list, \dn, \dt, \c, \l, \di, \q, show users, show, su - postgres, psql -c, \?, \connect, --version, --help, PL/pgSQL