ALTER EXTENSION UPGRADE patch v1

Hi,

Please find attached the patch to support ALTER EXTENSION UPGRADE,
following exchanges made on this list — we can't really speak about
decisions here, apparently, until commit is done :)

The documentation is available online for easy browsing here:

http://pgsql.tapoueh.org/extensions/doc/html/extend-extension.html

The things we might want to discuss are, AFAIUI:

- support for upgrading from pre-9.1 extension, or to get from a bunch
of related pl code to a proper extension in your database

I've done the code for that to work, the idea is pretty simple and
relies on the following points. Please note that the attached patch
only implements support for upgrading some contrib modules from
pre-9.1, that's because I'm willing to get some approvement before
continuing the effort — I foresee no road blocks here.

- CREATE WRAPPER EXTENSION

If you want to upgrade an extension, it first has to exists as an
extension. When you're wanting to switch to extension, you need a
way to bootstrap your extension object, because you want an entry in
the catalogs and you don't want to run the script: it has already
been run before you decided this would make for an extension.

This command allows you to register an extension in the catalogs,
bypassing any script and forcing the version to NULL.

I'm not sold on the 'WRAPPER' keyword here, I just used an existing
one in the grammar that looked like a good candidate. This was the
best I could find, but IANANS (I am not a native speaker).

- ALTER EXTENSION ... UPGRADE

This allows you to upgrade an existing extension, wrapper included.

The extension author needs to prepare the upgrade scripts, and to
setup in the control file which to use. The new extension's version
is static as the upgrade files you distribute depend on this (think
packaging here) and so you pick the upgrade script file to execute
depending only on the currently installed version.

This picking is made by regular expression matching (using the code
backing the ~(text, text) operator), and supports null as a special
case. The first match wins, other candidates are bypassed.

- CREATE EXTENSION ... WITH SYSID ...

Thinking about upgrades, I added support for that too. This might be
necessary for pg_upgrade, but I'm not so sure. It was an experiment
but I though we might as well talk about it before I remove it from
the patch :)

- ALTER OBJECT ... SET EXTENSION ...

This implements the magic behind "upgrading from null", as it allows
the users to add objects to an existing extension. Internally, this
will only record a INTERNAL depedency between the object and the
extension.

This is mainly for use in upgrade scripts when you support pre-9.1
extension upgrade, or for internal PL code that grows into an
extension after the fact.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support