Static DATABASE_TEMPLATE1 

pub static DATABASE_TEMPLATE1: &str

template1 is always present in a PostgreSQL cluster.

This database is used as the default template for creating new databases.

Connecting to a database prevents other sessions from creating new databases using that database as a template; see PostgreSQL’s Template Databases page to learn more about this limitation. Since template1 is the default template, connecting to this database prevents other sessions from using a plain CREATE DATABASE command. In other words, it may be a good idea to connect to this database only when modifying it, not as a default.