From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
cc: rekgrpth@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18247: Integer overflow leads to negative width
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Comments: In-reply-to Richard Guo <guofenglinux@gmail.com>
	message dated "Fri, 15 Dec 2023 10:28:10 +0800"
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Date: Fri, 15 Dec 2023 10:43:03 -0500
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Richard Guo <guofenglinux@gmail.com> writes:
> On Thu, Dec 14, 2023 at 10:43 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Probably better to clamp tuple width estimates to MaxAllocSize.
>> Anything larger would not correspond to reality anyhow.

> Fair point.  How about the attached patch?

We'd need to hit at least build_joinrel_tlist too.  Not sure
offhand whether this is enough to cover upper-relation tlists.

As far as the specifics go, is it enough to clamp once?  I think
we'd either have to clamp after each addition, or change the
running-sum variables to double and clamp just before storing
into the final width field.  The latter seems probably
less error-prone in the long run.

Also, given that we'll need at least three copies of the clamp
rule, I wonder if it's worth inventing a function comparable
to clamp_row_est().

			regards, tom lane