From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
Cc: rekgrpth@gmail.com
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18247: Integer overflow leads to negative width
Date: Fri, 15 Dec 2023 10:43:03 -0500
Message-ID: <2993260.1702654983@sss.pgh.pa.us> (raw)
In-Reply-To: <CAMbWs4_8+mtt5C8EXmfHa_Hs-OW6EhEz_XjhzBk8miwg2h65CQ@mail.gmail.com>
References: <18247-11ac477f02954422@postgresql.org>
<CAMbWs48nZf9XgAVpXbOnwGWWLnmoOZb51wnhkNW5xfz_PyOyCw@mail.gmail.com>
<2781181.1702565025@sss.pgh.pa.us>
<CAMbWs4_8+mtt5C8EXmfHa_Hs-OW6EhEz_XjhzBk8miwg2h65CQ@mail.gmail.com>
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
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, guofenglinux@gmail.com, rekgrpth@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18247: Integer overflow leads to negative width
In-Reply-To: <2993260.1702654983@sss.pgh.pa.us>
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