Re: Optimization for updating foreign tables in Postgres FDW

From: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
To: Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)com>
Cc: Thom Brown <thom(at)linux(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Shigeru Hanada <shigeru(dot)hanada(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Optimization for updating foreign tables in Postgres FDW
Date: 2016-02-15 09:35:07
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On 2016/02/15 15:20, Rushabh Lathia wrote:
> On Fri, Feb 12, 2016 at 5:40 PM, Etsuro Fujita
> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp <mailto:fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>> wrote:

> As a result of our discussions, we reached a conclusion that the DML
> pushdown APIs should be provided together with existing APIs such as
> ExecForeignInsert, ExecForeignUpdate or ExecForeignDelete, IIUC.
> So, how about (1) leaving the description for the existing APIs
> as-is and (2) adding a new description for the DML pushdown APIs in
> parenthesis, like this?:
> If the <function>IsForeignRelUpdatable</> pointer is set to
> <literal>NULL</>, foreign tables are assumed to be insertable,
> updatable,
> or deletable if the FDW provides <function>ExecForeignInsert</>,
> <function>ExecForeignUpdate</>, or <function>ExecForeignDelete</>
> respectively.
> (If the FDW attempts to optimize a foreign table update, it still
> needs to provide PlanDMLPushdown, BeginDMLPushdown,
> IterateDMLPushdown and EndDMLPushdown.)
> Actually, if the FDW provides the DML pushdown APIs, (pushdown-able)
> foreign table updates can be done without ExecForeignInsert,
> ExecForeignUpdate or ExecForeignDelete. So, the above docs are not
> necessarily correct. But we don't recommend to do that without the
> existing APIs, so I'm not sure it's worth complicating the docs.

> Adding a new description for DML pushdown API seems good idea. I would
> suggest to add that as separate paragraph rather then into brackets.

OK, will do.

Best regards,
Etsuro Fujita

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