Re: Optimization for updating foreign tables in Postgres FDW

From: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
To: Noah Misch <noah(at)leadboat(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Rushabh Lathia <rushabh(dot)lathia(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: 2016-04-04 10:49:02
Message-ID: 5702469E.4050709@lab.ntt.co.jp
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On 2016/03/31 16:38, Etsuro Fujita wrote:
> On 2016/03/31 14:07, Noah Misch wrote:
>> On Thu, Mar 24, 2016 at 01:02:57PM +0900, Etsuro Fujita wrote:
>>> On 2016/03/24 11:14, Michael Paquier wrote:
>>>> On Wed, Mar 23, 2016 at 10:05 PM, Thom Brown <thom(at)linux(dot)com> wrote:
>>>>> I've noticed that you now can't cancel a query if there's DML pushdown
>>>>> to a foreign server. This previously worked while it was sending
>>>>> individual statements as it interrupted and rolled it back.
>>>>>
>>>>> Here's what the local server sees when trying to cancel:
>>>>>
>>>>> # DELETE FROM remote.contacts;
>>>>> ^CCancel request sent
>>>>> DELETE 5000000
>>>>>
>>>>> This should probably be fixed.

>>>> Looking at what has been committed, execute_dml_stmt is using
>>>> PQexecParams, so we'd want to use an asynchronous call and loop on
>>>> PQgetResult with CHECK_FOR_INTERRUPTS() in it.

>>> Will fix.

>> [This is a generic notification.]

> Sorry for not having taken any action. I've been busy with another task
> lately, but I started working on this. I plan to post a patch early
> next week.

Here is a patch to fix this issue. As proposed by Michael, I modified
execute_dml_stmt so that it uses PQsendQueryParams, not PQexecParams.
Any comments are welcome.

Best regards,
Etsuro Fujita

Attachment Content-Type Size
pgfdw-direct-modify.patch text/x-patch 5.0 KB

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