Thread: BUG #16698: Create extension and search path

The following bug has been logged on the website:

Bug reference:      16698
Logged by:          Miha Vrhovnik
Email address:      miha.vrhovnik@gmail.com
PostgreSQL version: 13.0
Operating system:   Linux
Description:

The documentation states, that I can use search_path to define in which
schema the extension is going to be created, but this is clearly not
true..

postgres=# CREATE DATABASE test;
CREATE DATABASE
postgres=# CREATE SCHEMA foo1;
CREATE SCHEMA
postgres=# SET search_path = 'foo1';
SET
postgres=# CREATE EXTENSION ltree;
CREATE EXTENSION
postgres=# CREATE SCHEMA foo2;
CREATE SCHEMA
postgres=# SET search_path = 'foo2';
SET
postgres=# CREATE EXTENSION ltree;
ERROR:  extension "ltree" already exists
postgres=# SHOW search_path;
 search_path 
-------------
 foo2
(1 row)

It's the same with example from the documentation.(This continues in the
same session, so search_path is set to foo2 at first create extension)

postgres=# CREATE EXTENSION hstore;
CREATE EXTENSION
postgres=# SET search_path = 'foo1';
SET
postgres=# CREATE EXTENSION hstore;
ERROR:  extension "hstore" already exists

It's a shame that this doesn't work as documented as creating migrations or
tests where each test is run in different schema is more difficult.

BR,
Miha

On 03/11/2020 09:57, PG Bug reporting form wrote:
> The following bug has been logged on the website:
> 
> Bug reference:      16698
> Logged by:          Miha Vrhovnik
> Email address:      miha.vrhovnik@gmail.com
> PostgreSQL version: 13.0
> Operating system:   Linux
> Description:
> 
> The documentation states, that I can use search_path to define in which
> schema the extension is going to be created, but this is clearly not
> true..

To be precise, the documentation for CREATE EXTENSION 
(https://www.postgresql.org/docs/current/sql-createextension.html) says:

> schema_name
> 
> The name of the schema in which to install the extension's objects,
> given that the extension allows its contents to be relocated. The
> named schema must already exist. If not specified, and the
> extension's control file does not specify a schema either, the
> current default object creation schema is used.
> 
> If the extension specifies a schema parameter in its control file,
> then that schema cannot be overridden with a SCHEMA clause. Normally,
> an error will be raised if a SCHEMA clause is given and it conflicts
> with the extension's schema parameter. However, if the CASCADE clause
> is also given, then schema_name is ignored when it conflicts. The
> given schema_name will be used for installation of any needed
> extensions that do not specify schema in their control files.
> 
> Remember that the extension itself is not considered to be within any
> schema: extensions have unqualified names that must be unique
> database-wide. But objects belonging to the extension can be within
> schemas.
The first paragraph says "schema in which to install the extension's 
*objects*" (emphasis mine). And the last paragraph explains this more 
explicitly.

- Heikki

Miha Vrhovnik <miha.vrhovnik@gmail.com> writes:
> I'm so sorry, but I do not understand... Even if I force the schema in
> CREATE EXTENSION it still says that it already exists. (Tested on 12.4, but
> it's the same with 13, as I have tested it before)
> I'm missing something but the documentation doesn't state that I can only
> install extension once per database.

Extensions are not schema-qualified objects, so no, you cannot have
more than one instance per database.

            regards, tom lane

Miha Vrhovnik <miha.vrhovnik@gmail.com> writes:
> What are then extensions.. They live in some sort of limbo.. as they don't
> behave like a natural extension of the database... As they behave
> differently (because they "require" public shema in path if extensions are
> created while in public schema ).

You've got the wrong mental model.  Extensions are containers, which
may *contain* objects that live within schemas, but the extension itself
does not.  The key reason for doing it that way is that an extension might
itself contain a schema, or more than one schema.

            regards, tom lane