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Subject: Re: COPY JSON: use trailing commas in FORCE_ARRAY output
From: Daniel Gustafsson <daniel@yesql.se>
In-Reply-To: <DFAC4097-2559-4DED-B7D5-EB53B02E9DA3@gmail.com>
Date: Wed, 6 May 2026 10:23:53 +0200
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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References: <DFAC4097-2559-4DED-B7D5-EB53B02E9DA3@gmail.com>
To: Chao Li <li.evan.chao@gmail.com>
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> On 6 May 2026, at 08:40, Chao Li <li.evan.chao@gmail.com> wrote:

> I was surprised by the comma placement. It is valid JSON, but it looks =
quite uncommon.

It might look uncommon, but for very wide lines it's IMHO preferrable to =
not
have to scroll all the way to the end of the line to know that the line =
is part
of an array.

> For comparison, the existing json_agg() places commas at the end of =
the line:

That's true, but json_agg() and COPY TO in ndjson format have different =
use
cases.

> ..it should not have any performance impact.

It does add branches though, and in one branch use a non-inlined =
function where
previously it would unconditionally use an inline function.  ISTM it =
would
still be valuable to do performance testing given that COPY is commonly =
used in
performance sensitive settings.

--
Daniel Gustafsson