From: Andres Freund <andres@anarazel.de>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Prevent instability in contrib/pageinspect's regression test.
Date: Mon, 21 Nov 2022 11:56:28 -0800
Message-ID: <20221121195628.2rlqpbkjgjsvqn6w@alap3.anarazel.de> (raw)
In-Reply-To: <CA+TgmoaYMUv1ab2vAh7AoSUqUYHtPx9Cmehue2=JCXO3gvsDbw@mail.gmail.com>
References: <E1ox94a-000EHu-VH@gemulon.postgresql.org>
<20221121172206.h6kywxrzqcmhoqom@awork3.anarazel.de>
<3214376.1669051457@sss.pgh.pa.us>
<3215927.1669052115@sss.pgh.pa.us>
<CA+TgmoaYMUv1ab2vAh7AoSUqUYHtPx9Cmehue2=JCXO3gvsDbw@mail.gmail.com>
Hi,
On 2022-11-21 12:52:01 -0500, Robert Haas wrote:
> On Mon, Nov 21, 2022 at 12:35 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > I wrote:
> > > Andres Freund <andres@anarazel.de> writes:
> > >> Looks like a chunk of the buildfarm doesn't like this - presumably because
> > >> they use force_parallel_mode = regress. Seems ok to just force that to off in
> > >> this test?
> >
> > > Ugh ... didn't occur to me to try that. I'll take a look.
> >
> > Hmm, so the problem is:
> >
> > SELECT octet_length(get_raw_page('test1', 'main', 0)) AS main_0;
> > ERROR: cannot access temporary tables during a parallel operation
> >
> > Why in the world is get_raw_page() marked as parallel safe?
> > It clearly isn't, given this restriction.
>
> I suspect that restriction was overlooked when evaluating the marking
> of this function.
It's somewhat sad to add this restriction - I've used get_raw_page() (+
other functions) to scan a whole database for a bug. IIRC that actually
did end up using parallelism, albeit likely not very efficiently.
Don't really have a better idea though.
It may be worth inventing a framework where a function could analyze its
arguments (presumably via prosupport) to determine the degree of
parallel safety, but this doesn't seem sufficient reason...
Greetings
Andres Freund
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Cc: andres@anarazel.de, robertmhaas@gmail.com, tgl@sss.pgh.pa.us, pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Prevent instability in contrib/pageinspect's regression test.
In-Reply-To: <20221121195628.2rlqpbkjgjsvqn6w@alap3.anarazel.de>
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