Re: Oversight in reparameterize_path_by_child leading to executor crash

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От Richard Guo
Тема Re: Oversight in reparameterize_path_by_child leading to executor crash
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Msg-id CAMbWs484AW5AwzHZQFtEE2mrEZH8GrpHtjUks0gcixFPZfiJ5A@mail.gmail.com
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Ответ на Re: Oversight in reparameterize_path_by_child leading to executor crash  (Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>)
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On Fri, Sep 8, 2023 at 3:04 PM Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> wrote:
When the clause s.t1b = s.a is presented to distribute_qual_to_rels()
it has form PHV(t1.b) = t2.b. The PHV's ph_eval_at is 4, which is what
is returned as varno to pull_varnos(). The other Var in the caluse has
varno = 4 already so  pull_varnos() returns a SINGLETON relids (b 4).
The clause is an equality clause, so it is used to create an
Equivalence class.
generate_base_implied_equalities_no_const() then constructs the same
RestrictInfo again and adds to baserestrictinfo of Rel with relid = 4
i.e. t2's baserestrictinfo. I don't know whether that's the right
thing to do. 

Well, I think that's what PHVs are supposed to do.  Quoting the README:

... Note that even with this restriction, pullup of a LATERAL
subquery can result in creating PlaceHolderVars that contain lateral
references to relations outside their syntactic scope.  We still evaluate
such PHVs at their syntactic location or lower, but the presence of such a
PHV in the quals or targetlist of a plan node requires that node to appear
on the inside of a nestloop join relative to the rel(s) supplying the
lateral reference.
 
I am not sure where we are taking the original bug fix with this
investigation. Is it required to fix this problem in order to fix the
original problem OR we should commit the fix for the original problem
and then investigate this further?

Fair point.  This seems a separate problem from the original, so I'm
okay we fix them separately.

Thanks
Richard

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