Re: Partial aggregates pushdown

From: Jelte Fennema-Nio <postgres(at)jeltef(dot)nl>
To: "Fujii(dot)Yuki(at)df(dot)MitsubishiElectric(dot)co(dot)jp" <Fujii(dot)Yuki(at)df(dot)mitsubishielectric(dot)co(dot)jp>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Bruce Momjian <bruce(at)momjian(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net>, Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, vignesh C <vignesh21(at)gmail(dot)com>, Alexander Pyhalov <a(dot)pyhalov(at)postgrespro(dot)ru>
Subject: Re: Partial aggregates pushdown
Date: 2024-07-08 12:30:12
Message-ID: CAGECzQR_qwYupAEEVeY6sC14hQ9V2BGLNQQdROWvF60QmMsZFQ@mail.gmail.com
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On Mon, 8 Jul 2024 at 14:12, Fujii(dot)Yuki(at)df(dot)MitsubishiElectric(dot)co(dot)jp
<Fujii(dot)Yuki(at)df(dot)mitsubishielectric(dot)co(dot)jp> wrote:
> The best thing about Approach2 is that it lets us send state values using the existing data type system.
> I'm worried that if we choose Approach2, we might face some limits because we have to create new types.
> But, we might be able to fix these limits if we look into it more.
>
> Approach1 doesn't make new types, so we can avoid these limits.
> But, it means we have to make export/import functions that are similar to the typsend/typreceive functions.
> So, we need to make sure if we really need this method.
>
> Is this the right understanding?

Yeah, correct. To clarify my reasoning a bit more: IMHO, the main
downside of implementing Approach1 is that we then end up with two
different mechanisms to "take data from memory and serialize it in a
way in which it can be sent over the network". I'd very much prefer if
we could have a single system responsible for that task. So if there's
issues with the current system (e.g. having to implement
typinput/typoutput), then I'd rather address these problems in the
existing system. Only if that turns out to be impossible for some
reason, then I think I'd prefer Approach1.

Personally, even if the Approach2 requires a bit more code, then I'd
still prefer a single serialization system over having two
serializiation systems.

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