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Subject: Re: Making jsonb_agg() faster
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: <2329959.1765047648@sss.pgh.pa.us>
Date: Sun, 7 Dec 2025 08:13:42 +0800
Cc: jian he <jian.universality@gmail.com>,
 pgsql-hackers@lists.postgresql.org
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To: Tom Lane <tgl@sss.pgh.pa.us>
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> On Dec 7, 2025, at 03:00, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>=20
> Chao Li <li.evan.chao@gmail.com> writes:
>> On Dec 6, 2025, at 07:14, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> I'd kind of like to get this pushed soon, because it keeps getting
>>> sideswiped ... does anyone have further comments?
>=20
>> My only nit commit is still about the hard-coded 12:
>> I commented this before and you explained. But I still think it may =
deserve a comment for why 12 is here, otherwise future reader may also =
get the same confusion as when I first time read this code.
>=20
> I've been thinking of that as an independent issue.  But what I'm
> inclined to do is add a symbol to date.h, say like
>=20
> diff --git a/src/include/utils/date.h b/src/include/utils/date.h
> index 7316ac0ff17..2aca785b65d 100644
> --- a/src/include/utils/date.h
> +++ b/src/include/utils/date.h
> @@ -30,6 +30,14 @@ typedef struct
> int32 zone; /* numeric time zone, in seconds */
> } TimeTzADT;
>=20
> +/*
> + * sizeof(TimeTzADT) will be 16 on most platforms due to alignment =
padding.
> + * However, timetz's typlen is 12 according to pg_type.  In most =
places
> + * we can get away with using sizeof(TimeTzADT), but where it's =
important
> + * to match the declared typlen, use TIMETZ_TYPLEN.
> + */
> +#define TIMETZ_TYPLEN 12
> +
> /*
>  * Infinity and minus infinity must be the max and min values of =
DateADT.
>  */
>=20
> and then use that.  (I poked around in other code using TimeTzADT,
> and could not find any other places where we have hard-wired "12",
> which seems a bit surprising perhaps.  But pretty much all the
> references to sizeof(TimeTzADT) are in palloc's, where it's fine.)

That=E2=80=99s even better than resolving my comment.

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