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Re: objects tied to missing extension

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Phil Sorber <phil(at)omniti(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: objects tied to missing extension
Date: 2011-11-28 20:12:22
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugs
Phil Sorber <phil(at)omniti(dot)com> writes:
> I stumbled upon this situation when playing with extension upgrades.
> The problem I was having was that auto-generated datatypes were also
> being added to the extension and it wasn't obvious this was happening.
> I know this has been changed in 9.1 stable and in master.

I couldn't replicate any funnies with the given test case in 9.1 branch
tip.  (It might not work nicely if you change the upgrade script to do
DROP EXTENSION, but I cannot imagine any sane reason to do that ... and
we are assuming that extension script authors are responsible adults,
since the scripts are generally executed with superuser permissions.)

After poking in the code for awhile, I believe that the reason you had a
problem when the table's rowtype is an extension member is that the
deletion proceeds like this:

1. We start at table table_a, which is a legitimate drop request.
2. We recurse to its internal dependency, the rowtype table_a, and
decide that that's legitimate to drop too.
3. Recursing again, findDependentObjects finds the extension, and since
it's not at the outermost recursion level, decides that it ought to
proceed with deleting the extension.

The reason for this behavior is that we want to support deletion of
dependent extensions --- that is, if some object in extension A depends
on some object in extension B, and extension B is dropped with CASCADE,
then extension A ought to go away too.  So the decision at step 3 is not
wrong for such cases.  It might be that there's some corner case where
we need to tighten the rules, but AFAICS it's safe as long as every
directly-deletable object that's within an extension has a direct
dependency on the extension.  (That's enough to ensure that a DROP on
the object will encounter the extension at outermost recursion level.)
So the problem seems to be only due to your ALTER EXTENSION DROP command
having left an incomplete set of extension dependencies behind.

			regards, tom lane

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