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From: Robert Haas <[email protected]>
To: Andres Freund <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Bharath Rupireddy <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Issue with cancel_before_shmem_exit while searching to remove a particular registered exit callbacks
Date: Mon, 20 Jul 2020 15:47:00 -0400
Message-ID: <CA+TgmoZDFyV1RAmTEKvjaV8TvvS+gKha+RRiJUGMOLoY0-8Ekw@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <CALj2ACWk7j4F2v2fxxYfrroOF=AdFNPr1WsV+AGtHAFQOqm_pw@mail.gmail.com>
	<[email protected]>
	<[email protected]>

On Tue, Jul 7, 2020 at 12:55 PM Andres Freund <[email protected]> wrote:
> What are you proposing? For now we could easily enough work around this
> by just making it a on_proc_exit() callback, but that doesn't really
> change the fundamental issue imo.

I think it would be more correct for it to be an on_proc_exit()
callback, because before_shmem_exit() callbacks can and do perform
actions which rely on an awful lot of the system being still in a
working state. RemoveTempRelationsCallback() is a good example: it
thinks it can start and end transactions and make a bunch of catalog
changes. I don't know that any of that could use JIT, but moving the
JIT cleanup to the on_shmem_exit() stage seems better. At that point,
there shouldn't be anybody doing anything that relies on being able to
perform logical changes to the database; we're just shutting down
low-level subsystems at that point, and thus presumably not doing
anything that could possibly need JIT.

But I also agree that what pg_start_backup() was doing before v13 was
wrong; that's why I committed
303640199d0436c5e7acdf50b837a027b5726594. The only reason I didn't
back-patch it is because the consequences are so minor I didn't think
it was worth worrying about. We could, though. I'd be somewhat
inclined to both do that and also change LLVM to use on_proc_exit() in
master, but I don't feel super-strongly about it.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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