From: Antonin Houska <ah@cybertec.at>
To: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrew Gierth <andrew@tao11.riddles.org.uk>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Problems with plan estimates in postgres_fdw
Date: Tue, 12 Feb 2019 12:43:34 +0100
Message-ID: <26618.1549971814@localhost> (raw)
In-Reply-To: <5C6251A7.40204@lab.ntt.co.jp>
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Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote:
> (2019/02/08 21:35), Etsuro Fujita wrote:
> > (2019/02/08 2:04), Antonin Houska wrote:
> >> * add_foreign_ordered_paths()
> >>
> >> Exprssion root->upper_targets[UPPERREL_FINAL] is used to access the
> >> target.
> >>
> >> I think create_ordered_paths() should actually set the target so that
> >> postgresGetForeignUpperPaths() can simply find it in
> >> output_rel->reltarget. This is how postgres_fdw already retrieves the
> >> target
> >> for grouped paths. Small patch is attached that makes this possible.
> >
> > Seems like a good idea. Thanks for the patch! Will review.
>
> Here are my review comments:
>
> root->upper_targets[UPPERREL_FINAL] = final_target;
> + root->upper_targets[UPPERREL_ORDERED] = final_target;
> root->upper_targets[UPPERREL_WINDOW] = sort_input_target;
> root->upper_targets[UPPERREL_GROUP_AGG] = grouping_target;
>
> I think that's a good idea. I think we'll soon need the PathTarget for
> UPPERREL_DISTINCT, so how about saving that as well like this?
>
> root->upper_targets[UPPERREL_FINAL] = final_target;
> + root->upper_targets[UPPERREL_ORDERED] = final_target;
> + root->upper_targets[UPPERREL_DISTINCT] = sort_input_target;
> root->upper_targets[UPPERREL_WINDOW] = sort_input_target;
> root->upper_targets[UPPERREL_GROUP_AGG] = grouping_target;
I see nothing wrong about this.
> Another is about this:
>
> /*
> + * Set reltarget so that it's consistent with the paths. Also it's more
> + * convenient for FDW to find the target here.
> + */
> + ordered_rel->reltarget = target;
>
> I think this is correct if there are no SRFs in the targetlist, but otherwise
> I'm not sure this is really correct because the relation's reltarget would not
> match the target of paths added to the relation after adjust_paths_for_srfs().
I wouldn't expect problem here. create_grouping_paths() also sets the
reltarget although adjust_paths_for_srfs() can be alled on grouped_rel
afterwards.
--
Antonin Houska
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26, A-2700 Wiener Neustadt
Web: https://www.cybertec-postgresql.com
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To: pgsql-hackers@postgresql.org
Cc: ah@cybertec.at, fujita.etsuro@lab.ntt.co.jp, tgl@sss.pgh.pa.us, andrew@tao11.riddles.org.uk
Subject: Re: Problems with plan estimates in postgres_fdw
In-Reply-To: <26618.1549971814@localhost>
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