| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
| Cc: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Antonin Houska <ah(at)cybertec(dot)at>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Removing [Merge]Append nodes which contain a single subpath |
| Date: | 2017-10-26 20:06:05 |
| Message-ID: | 9810.1509048365@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> On 27 October 2017 at 01:44, Ashutosh Bapat
> <ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
>> I think Antonin has a point. The join processing may deem some base
>> relations dummy (See populate_joinrel_with_paths()). So an Append
>> relation which had multiple child alive at the end of
>> set_append_rel_size() might ultimately have only one child after
>> partition-wise join has worked on it.
TBH, that means partition-wise join planning is broken and needs to be
redesigned. It's impossible that we're going to make sane planning
choices if the sizes of relations change after we've already done some
planning work.
regards, tom lane
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