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help / color / mirror / Atom feedFrom: David Rowley <[email protected]>
To: Richard Guo <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Tender Wang <[email protected]>
Cc: Paul George <[email protected]>
Cc: Andy Fan <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Cc: [email protected]
Cc: Matheus Alcantara <[email protected]>
Subject: Re: Eager aggregation, take 3
Date: Thu, 9 Oct 2025 00:14:39 +1300
Message-ID: <CAApHDvr4YWpiMR3RsgYwJWv-u8xoRqTAKRiYy9zUszjZOqG4Ug@mail.gmail.com> (raw)
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On Tue, 7 Oct 2025 at 23:57, Richard Guo <[email protected]> wrote:
>
> On Mon, Oct 6, 2025 at 10:59 PM David Rowley <[email protected]> wrote:
> > 6. Shouldn't this be using lappend()?
> >
> > agg_clause_list = list_append_unique(agg_clause_list, ac_info);
> >
> > I don't understand why ac_info could already be in the list. You've
> > just done: ac_info = makeNode(AggClauseInfo);
>
> A query can specify the same Aggref expressions multiple times in the
> target list. Using lappend here can lead to duplicate partial Aggref
> nodes in the targetlist of a grouped path, which is what I want to
> avoid.
I was getting that mixed up with list_append_unique_ptr().
> > 9. In get_expression_sortgroupref(), a comment claims "We ignore child
> > members here.". I think that's outdated since ec_members no longer has
> > child members.
>
> I think that comment is used to explain why we only scan ec_members
> here. Similar comments can be found in many other places, such as in
> equivclass.c:
>
> /*
> * Found our match. Scan the other EC members and attempt to generate
> * joinclauses. Ignore children here.
> */
> foreach(lc2, cur_ec->ec_members)
> {
I'd say that's also wrong. "Ignore" means not to pay attention to
something that's there. The child members are not there.
> > 11. The way you've written the header comments for typedef struct
> > RelAggInfo seems weird. I've only ever seen extra details in the
> > header comment when the inline comments have been kept to a single
> > line. You're spanning multiple lines, so why have the out of line
> > comments in the header at all?
> I've also updated the comments within RelAggInfo to use one-line
> style.
The style I'd thought of had the comments on the same line as the
field. Something like struct EquivalenceClass.
>I wrapped the long queries in v24.
+-- Enable eager aggregation, which by default is disabled.
+SET enable_eager_aggregate TO on;
The above comment and command mismatch to my understanding from
looking at postgresql.conf.sample and guc_parameters.dat.
David
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Subject: Re: Eager aggregation, take 3
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