From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dmitry Ivanov <d.ivanov@postgrespro.ru>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Possible problem in Custom Scan API
Date: Mon, 17 Apr 2017 15:33:35 -0400
Message-ID: <29429.1492457615@sss.pgh.pa.us> (raw)
In-Reply-To: <e9c265ef-3b63-46bd-8b61-8612f684057e@postgrespro.ru>
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<1ef85b46-1385-4810-bb80-97cd977da1d5@postgrespro.ru>
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<f7590622-182b-4362-b148-c21de109ad2a@postgrespro.ru>
<4509.1491944329@sss.pgh.pa.us>
<0e0388a6-aa53-42a6-8be9-0d46ccbc788e@postgrespro.ru>
<8130.1492013026@sss.pgh.pa.us>
<e9c265ef-3b63-46bd-8b61-8612f684057e@postgrespro.ru>
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Dmitry Ivanov <d.ivanov@postgrespro.ru> writes:
> Tom Lane wrote:
>> I'm coming around to the idea that it'd be better to disable physical
>> tlists for custom scans.
>> However, I'm hesitant to make such a change in the back branches; if
>> there's anyone using custom scans who's negatively affected, they'd be
>> rightfully unhappy. Are you satisfied if we change this in HEAD?
After thinking about this over the weekend, I've come to the conclusion
that back-patching is probably the right thing anyway. The upside of the
use_physical_tlist optimization is pretty marginal even when it applies,
while the downsides of applying it inappropriately can be very large,
as we've discussed.
> I've been thinking about this all along, and it seems that this is a decent
> decision. However, I've made a tiny bugfix patch which allows CustomScans
> to notify the core code that they can handle physical targetlists.
I'm unimpressed by this part --- we couldn't back-patch such a change, and
I think it's unnecessary anyway in 9.6+ because the scan provider could
generate a nondefault pathtarget if it wants this to happen.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, d.ivanov@postgrespro.ru
Subject: Re: Possible problem in Custom Scan API
In-Reply-To: <29429.1492457615@sss.pgh.pa.us>
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