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Subject: Re: Trivial Fix: use palloc_array/repalloc_array for BufFile file
 arrays
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: 
 <CAD21AoDwp1D6-xm3p28RvUJKHcZM+9YtjUzNk38kLitN_Nbq4Q@mail.gmail.com>
Date: Mon, 9 Mar 2026 08:40:29 +0800
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>
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To: Masahiko Sawada <sawada.mshk@gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/E9EAE2FC-94A2-4128-A447-927927D5DD26%40gmail.com>
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> On Mar 7, 2026, at 03:33, Masahiko Sawada <sawada.mshk@gmail.com> =
wrote:
>=20
> Hi,
>=20
> On Tue, Mar 3, 2026 at 5:31=E2=80=AFPM Chao Li =
<li.evan.chao@gmail.com> wrote:
>>=20
>>=20
>>=20
>>> On Dec 25, 2025, at 11:34, Chao Li <li.evan.chao@gmail.com> wrote:
>>>=20
>>>=20
>>>=20
>>>> On Dec 25, 2025, at 11:12, Chao Li <li.evan.chao@gmail.com> wrote:
>>>>=20
>>>> Hi Hackers,
>>>>=20
>>>> I noticed this error while working on [1].
>>>>=20
>>>> In BufFile, the fields is claimed as an array:
>>>> ```
>>>> struct BufFile
>>>> {
>>>>   File *files; /* palloc'd array with numFiles entries */
>>>> ```
>>>>=20
>>>> However, it=E2=80=99s allocated by palloc_object():
>>>> ```
>>>> file->files =3D palloc_object(File);
>>>> ```
>>>>=20
>>>> And reallocated by repalloc():
>>>> ```
>>>>   file->files =3D (File *) repalloc(file->files,
>>>>       (file->numFiles + 1) * sizeof(File));
>>>> ```
>>>>=20
>>>> This trivial patch just changes to use palloc_array/repalloc_array, =
which makes the intent clearer.
>>>>=20
>>>> Best regards,
>>>> --
>>>> Chao Li (Evan)
>>>> HighGo Software Co., Ltd.
>>>> https://www.highgo.com/
>>>>=20
>>>>=20
>>>>=20
>>>>=20
>>>> <v1-0001-Use-palloc_array-repalloc_array-for-BufFile-file-.patch>
>>>=20
>>>=20
>>> Sorry for missing the reference of [1]:
>>>=20
>>> [1] https://postgr.es/m/aUStrqoOCDRFAq1M@paquier.xyz
>>>=20
>>> Best regards,
>>> --
>>> Chao Li (Evan)
>>> HighGo Software Co., Ltd.
>>> https://www.highgo.com/
>>>=20
>>=20
>> PFA v2:
>> * Rebased
>> * Updated the commit message
>=20
> I've reviewed the v2 patch and here is a comment:
>=20
> - file->files =3D palloc_object(File);
> + file->files =3D palloc_array(File, 1);
>=20
> I'm not a fan of this change. This change looks like trying to
> distinguish allocated memory by palloc_object() and palloc_array()
> even though underlying memory is identical. I'm concerned about this
> change creating unnecessary coding conventions.
>=20

Hi Masahiho-san,

Thank you so much for taking the time to review this patch.

Actually, this change was my original motivation for creating the patch. =
When I first read the code, I was confused why the field was named with =
the plural =E2=80=9Cfiles" even though it was allocated with =
palloc_object(). After reading further, I saw that the memory is later =
enlarged with repalloc, so it became clear that file->files is really =
meant to be an array.

To me, the allocation method should reflect the actual meaning of the =
object. Here, file->files is an array, no matter how many elements it =
currently contains. Even if it only has one element at the moment, =
semantically it is still an array.

By =E2=80=9Ccreating unnecessary coding conventions=E2=80=9D, are you =
concerned that this change might encourage people to always use =
palloc_array(type, 1) when allocating a single object? That concern is =
understandable, but I think it should depend on the real semantics. If =
the memory is for a single object, then of course palloc_array() should =
be wrong.

Given the nature of C, a "File *" can point either to a single File =
object or to a File array. In that sense, palloc_array() makes it =
explicit that this pointer is intended to represent an array, while =
palloc_object() suggests a single object. So I think changing this to =
palloc_array() improves readability in this case.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/