From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: pgsql-hackers@postgresql.org
Subject: Re: Protection lost in expression eval changeover
In-reply-to: <20170328181324.e47nypa4vqg3dpk4@alap3.anarazel.de>
References: <16803.1490723570@sss.pgh.pa.us>
 <20170328181324.e47nypa4vqg3dpk4@alap3.anarazel.de>
Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Tue, 28 Mar 2017 11:13:24 -0700"
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Date: Tue, 28 Mar 2017 14:43:38 -0400
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Andres Freund <andres@anarazel.de> writes:
> On 2017-03-28 13:52:50 -0400, Tom Lane wrote:
>> So it seems like we are missing some needed protection.  I'm inclined
>> to think that it'd be all right to just throw an error immediately in
>> CheckVarSlotCompatibility if the target column is dropped.

> Hm - so far we've pretty widely only set columns to NULL in that
> case. You don't see concerns with triggering errors in cases we
> previously hadn't?

Well, in principle these errors ought to be unreachable at all; they're
only there to backstop any possible failure to notice stale plans.
I don't see a strong reason why we need to allow a dropped column to go
to null while we throw an immediate error for a change in column type.
(If there is some reason, hopefully beta testing will find it.)

> I wonder if it'd not be better to add a branch to slot_deform_tuple's
> main loop like

Much rather not do that.

			regards, tom lane


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