866566a690
Commit 803716013dc1350f installed a safeguard against loading plpython2 and plpython3 at the same time, but asserted that both could still be used in the same database, just not in the same session. However, that's not actually all that practical because dumping and reloading will fail (since both libraries necessarily get loaded into the restoring session). pg_upgrade is even worse, because it checks for missing libraries by loading every .so library mentioned in the entire installation into one session, so that you can have only one across the whole cluster. We can improve matters by not throwing the error immediately in _PG_init, but only when and if we're asked to do something that requires calling into libpython. This ameliorates both of the above situations, since while execution of CREATE LANGUAGE, CREATE FUNCTION, etc will result in loading plpython, it isn't asked to do anything interesting (at least not if check_function_bodies is off, as it will be during a restore). It's possible that this opens some corner-case holes in which a crash could be provoked with sufficient effort. However, since plpython only exists as an untrusted language, any such crash would require superuser privileges, making it "don't do that" not a security issue. To reduce the hazards in this area, the error is still FATAL when it does get thrown. Per a report from Paul Jones. Back-patch to 9.2, which is as far back as the patch applies without work. (It could be made to work in 9.1, but given the lack of previous complaints, I'm disinclined to expend effort so far back. We've been pretty desultory about support for Python 3 in 9.1 anyway.)
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