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From: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Date: Wed, 14 Feb 2018 15:34:52 +0530
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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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On Wed, Feb 14, 2018 at 2:50 PM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
>
> I'd vote for #1, but ISTM that that's more like a feature, not a fix.
> Pushing down ConvertRowtypeExprs to the remote seems to me to be the same
> problem as pushing down PHVs to the remote, which is definitely a feature
> development.  I think a fix for this would be to just give up pushing down a
> child join in foreign_join_ok or somewhere else if the reltarget of the
> child-join relation contains any ConvertRowtypeExprs.

That means we won't be able to push down any scans under a DML on a
partitioned table. That will be too restrictive.

I think the case of PHV and ConvertRowtypeExprs are different. The the
former we need a subquery to push PHVs, whereas to deparse
ConvertRowtypeExpr on the nullable side we can use the same strategy
as whole-row expression deparsing.

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