Re: [HACKERS] [Proposal] Make the optimiser aware of partitions ordering

From: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
To: Julien Rouhaud <rjuju123(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, pgsql-hackers Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] [Proposal] Make the optimiser aware of partitions ordering
Date: 2017-11-29 02:14:05
Message-ID: CAB7nPqQuvRZtz0rpPR0DKEb=mKjioTPFZdpPiqW1O16TsDZ7og@mail.gmail.com
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On Wed, Sep 27, 2017 at 2:59 AM, Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
> On Tue, Sep 26, 2017 at 2:56 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Sat, Sep 23, 2017 at 6:29 AM, Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
>>> That's true, but numCols, sortColdIdx etc are also used to display the
>>> sort key in an explain. If an append can return sorted data, it
>>> should also display the sort information, so I think these fields are
>>> still required in an Append node.
>>
>> I don't think so. An index scan doesn't output that information, nor
>> does a nested loop which inherits a sort order from its outer path. I
>> think the rule is that a plan node which takes steps to get the data
>> into a certain order might want to output something about that, but a
>> plan node which somehow gets that ordering without taking any explicit
>> action doesn't print anything.
>
> Oh, ok that indeed makes sense. As I said I'll remove all the useless
> noise and send an updated patch. Thanks again.

Waiting for a patch update for two months now, so marked as returned
with feedback.
--
Michael

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