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From: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Date: Thu, 10 May 2018 09:34:33 +0530
Message-ID: 
 <CAFjFpRcFucgvrzEFNi10g00-va640poSmJDmBrZNfFarB6eP-Q@mail.gmail.com>
Subject: Re: Expression errors with "FOR UPDATE" and postgres_fdw with
 partition wise join enabled.
To: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
Cc: Rajkumar Raghuwanshi <rajkumar.raghuwanshi@enterprisedb.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
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Precedence: bulk

On Wed, May 9, 2018 at 5:20 PM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
>
> (2018/04/25 18:51), Ashutosh Bapat wrote:
>> Actually I noticed that ConvertRowtypeExpr are used to cast a child's
>> whole row reference expression (not just a Var node) into that of its
>> parent and not. For example a cast like NULL::child::parent produces a
>> ConvertRowtypeExpr encapsulating a NULL constant node and not a Var
>> node. We are interested only in ConvertRowtypeExprs embedding Var
>> nodes with Var::varattno = 0. I have changed this code to use function
>> is_converted_whole_row_reference() instead of the above code with
>> Assert. In order to use that function, I had to take it out of
>> setrefs.c and put it in nodeFuncs.c which seemed to be a better fit.
>
> This change seems a bit confusing to me because the flag bits
> "PVC_INCLUDE_CONVERTROWTYPES" and "PVC_RECURSE_CONVERTROWTYPES" passed to
> pull_var_clause look as if it handles any ConvertRowtypeExpr nodes from a
> given clause, but really, it only handles ConvertRowtypeExprs you mentioned
> above.  To make that function easy to understand and use, I think it'd be
> better to use the IsA(node, ConvertRowtypeExpr) test as in the first version
> of the patch, instead of is_converted_whole_row_reference, which would be
> more consistent with other cases such as PlaceHolderVar.

I agree that using is_converted_whole_row_reference() is not
consistent with the other nodes that are handled by pull_var_clause().
I also agree that PVC_*_CONVERTROWTYPES doesn't reflect exactly what's
being done with those options. But using
is_converted_whole_row_reference() is the correct thing to do since we
are interested only in the whole-row references embedded in
ConvertRowtypeExpr. There can be anything encapsulated in
ConvertRowtypeExpr(), a non-shippable function for example. We don't
want to try to push that down in postgres_fdw's case. Neither in other
cases. So, it boils down to changing names of PVC_*_CONVERTROWTYPES to
something more meaningful. How about PVC_*_CONVERTWHOLEROWS?

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company