CREATE DATABASE will fail if any other connection exists when it starts during the copy operation, new connections to the source database are prevented. The principal limitation is that no other sessions can be connected to the source database while it is being copied. It is important to understand, however, that this is not (yet) intended as a general-purpose “ COPY DATABASE” facility. It is possible to create additional template databases, and indeed one can copy any database in a cluster by specifying its name as the template for CREATE DATABASE. To create a database by copying template0, use:ĬREATE DATABASE dbname TEMPLATE template0 This is because template1 might contain encoding-specific or locale-specific data, while template0 is known not to. This is particularly handy when restoring a pg_dump dump: the dump script should be restored in a pristine database to ensure that one recreates the correct contents of the dumped database, without conflicting with objects that might have been added to template1 later on.Īnother common reason for copying template0 instead of template1 is that new encoding and locale settings can be specified when copying template0, whereas a copy of template1 must use the same settings it does. By instructing CREATE DATABASE to copy template0 instead of template1, you can create a “ pristine” user database (one where no user-defined objects exist and where the system objects have not been altered) that contains none of the site-local additions in template1. template0 should never be changed after the database cluster has been initialized. This database contains the same data as the initial contents of template1, that is, only the standard objects predefined by your version of PostgreSQL. There is a second standard system database named template0. For example, if you install the procedural language PL/Perl in template1, it will automatically be available in user databases without any extra action being taken when those databases are created. This behavior allows site-local modifications to the standard set of objects in databases. If you add objects to template1, these objects will be copied into subsequently created user databases. Thus that database is the “ template” from which new databases are made. By default, it copies the standard system database named template1. CREATE DATABASE actually works by copying an existing database.
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