Hi, On Wed, Nov 09, 2022 at 09:16:40PM -0800, Adrian Klaver wrote: > On 11/9/22 20:57, Ian Lawrence Barwick wrote: > > > > template0 and template1 are the mandatory system databases which > > cannot be dropped. > > Actually that is not strictly true: > > https://www.postgresql.org/docs/current/manage-ag-templatedbs.html > > " > Note > > template1 and template0 do not have any special status beyond the fact that > the name template1 is the default source database name for CREATE DATABASE. > For example, one could drop template1 and recreate it from template0 without > any ill effects. This course of action might be advisable if one has > carelessly added a bunch of junk in template1. (To delete template1, it must > have pg_database.datistemplate = false.) > > The postgres database is also created when a database cluster is > initialized. This database is meant as a default database for users and > applications to connect to. It is simply a copy of template1 and can be > dropped and recreated if necessary. > " And one important thing about template0 is that postgres will assume that it only contains identifiers with plain ASCII characters, so that the on-disk data is compatible with any encoding (at least any supported server encoding, stuff like EBCDIC clearly wouldn't play well with that assumption), and can therefore be used to create a new database with a different encoding from template1 (or another template database). Breaking that assumption is usually a very bad idea.
