From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
---|---|
To: | Richard Guo <guofenglinux(at)gmail(dot)com> |
Cc: | Alexander Lakhin <exclusion(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Properly pathify the union planner |
Date: | 2024-03-27 09:47:54 |
Message-ID: | CAApHDvq1mJWSwQwDTcpRpqipsv4grSR+NQ5FWgB6hfK_ZQOJAg@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, 27 Mar 2024 at 16:15, Richard Guo <guofenglinux(at)gmail(dot)com> wrote:
> if (root->parent_root != NULL &&
> root->parent_root->parse->setOperations != NULL &&
> IsA(root->parent_root->parse->setOperations, SetOperationStmt))
> qp_extra.setop =
> (SetOperationStmt *) root->parent_root->parse->setOperations;
> else
> qp_extra.setop = NULL;
>
> This check cannot tell if the subquery is for a set operation or a CTE,
> because its parent might have setOperations set in both cases. Hmm, is
> there any way to differentiate between the two?
As far as I see, there's nothing to go on... well unless you counted
canSetTag, which is false for the CTE (per analyzeCTE())... but that's
certainly not the fix.
I did wonder when first working on this patch if subquery_planner()
should grow an extra parameter, or maybe consolidate some existing
ones by passing some struct that provides the planner with a bit more
context about the query. A few of the existing parameters are likely
candidates for being in such a struct. e.g. hasRecursion and
tuple_fraction. A SetOperationStmt could go in there too.
The other CTE thread about the PathKey change you worked on highlights
that something like this could be useful. I posted in [1] about this.
David
[1] https://postgr.es/m/CAApHDvrF53ErmonnpO77eDiJm7PyReZ+nD=4FSsSOmaKx6+MuQ@mail.gmail.com
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