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Subject: Re: RFC: Additional Directory for Extensions
From: "David E. Wheeler" <david@justatheory.com>
In-Reply-To: <04235387-120e-4bf6-b5c8-645d869222b9@eisentraut.org>
Date: Tue, 12 Nov 2024 09:44:52 -0500
Cc: Craig Ringer <craig.ringer@enterprisedb.com>,
 Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>,
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To: Peter Eisentraut <peter@eisentraut.org>
Archived-At: <https://www.postgresql.org/message-id/DA13F479-6587-4841-AD53-F3D08BBBA08B%40justatheory.com>
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On Nov 12, 2024, at 08:25, Peter Eisentraut <peter@eisentraut.org> =
wrote:

> No, you can also install them into a common directory and mount that =
one.  For example, you install the extension at build time into =
/tmp/foo/{lib,share/extension}, you package that up as a disk image, =
mount it at /opt/extensions/myext, and then you can point =
extension_control_path at /opt/extensions/myext/lib and =
dynamic_library_path at /opt/extensions/myext/share/extension.

Ah, I see, then you just have to set both GUCs to subdirectories of the =
one volume.

>> Since that=E2=80=99s set at build/install time, couldn=E2=80=99t the =
definition of `$libdir` here be changed to mean =E2=80=9Cthe directory =
into which it=E2=80=99s being installed right now?=E2=80=9D. Doesn=E2=80=99=
t seem necessary to search a path if the specific location is set at =
install time.
>=20
> No, this is not set at build or install time.  This is for typical =
extensions hardcoded, and $libdir is resolved by the PostgreSQL server =
at run time.

I see, so that they could be moved and, as long as dynamic_library_path =
is updated, would still be findable.

So back to your original caveat:

>>> - The biggest problem is that many extensions set in their control =
file
>>>=20
>>>    module_pathname =3D '$libdir/foo'
>>>=20
>>> This disables the use of dynamic_library_path, so this whole idea of =
installing an extension elsewhere won't work that way.  The obvious =
solution is that extensions change this to just 'foo'.  But this will =
require a lot updating work for many extensions, or a lot of patching by =
packagers.

Yeah, '$libdir/foo' has been the documented way to do it for quite some =
time, as I recall. Perhaps the behavior of the MODULE_PATHNAME =
replacement function could be changed to omit $libdir when writing the =
SQL files?

>> Perhaps I misunderstand, but I would like to talk through the =
implications of a more radical rethinking of extension file location =
along the lines of the other thread[2] and the RFC I=E2=80=99m working =
up based on them both[1], especially since there are a few other use =
cases that inform it.
>=20
> I'm aware of that thread, but I think that is looking like a much =
larger project than what I'm proposing here.

Fair enough. Once we get to some consensus on a design there (and I=E2=80=99=
ve continued to iterate on it elsewhere[1]), I doubt it=E2=80=99d take =
much to use this patch as the first step toward it.

Best,

David

[1]: https://github.com/theory/justatheory/pull/7/files