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From: Richard Guo <guofenglinux@gmail.com>
Date: Thu, 9 Jan 2025 18:27:06 +0900
Message-ID: <CAMbWs4_2T25cEnptbHHLVO2Dw-jwDaLsjK+72WJ18jrw75V2mw@mail.gmail.com>
Subject: Re: Eager aggregation, take 3
To: jian he <jian.universality@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tender Wang <tndrwang@gmail.com>, 
	Paul George <p.a.george19@gmail.com>, Andy Fan <zhihuifan1213@163.com>, 
	PostgreSQL-development <pgsql-hackers@postgresql.org>, pgsql-hackers@lists.postgresql.org
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Precedence: bulk

On Thu, Jan 9, 2025 at 12:15=E2=80=AFPM jian he <jian.universality@gmail.co=
m> wrote:
> hi.
> in create_grouping_expr_infos
>
>         tce =3D lookup_type_cache(exprType((Node *) tle->expr),
>                                 TYPECACHE_BTREE_OPFAMILY);
>         if (!OidIsValid(tce->btree_opf) ||
>             !OidIsValid(tce->btree_opintype))
>             return;
>        ....
>         /*
>          * Get the operator in the btree's opfamily.
>          */
>         eq_op =3D get_opfamily_member(tce->btree_opf,
>                                     tce->btree_opintype,
>                                     tce->btree_opintype,
>                                     BTEqualStrategyNumber);
>         if (!OidIsValid(eq_op))
>             return;
>         eq_opfamilies =3D get_mergejoin_opfamilies(eq_op);
>         if (!eq_opfamilies)
>             return;
>         btree_opfamily =3D linitial_oid(eq_opfamilies);
>
>
> If eq_op is valid, then we don't need to call get_mergejoin_opfamilies?
> since get_mergejoin_opfamilies output will be the same as tce->btree_opf.
> and we already checked (tce->btree_opf) is valid.
>
> In other words, I think eq_op is valid imply
> that tce->btree_opf is the value (btree opfamily) we need.

Nice catch!  Actually, we can use tce->btree_opf directly, without
needing to check its equality operator, since we know it's a btree
opfamily and it's valid.  If it were a different opfamily (such as a
hash opfamily), we would need to look up its equality operator, and
select some btree opfamily that that operator is part of.  But in this
case, that's not necessary.

Thanks
Richard