Re: speeding up planning with partitions

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: "Imai, Yoshikazu" <imai(dot)yoshikazu(at)jp(dot)fujitsu(dot)com>
Cc: "'Amit Langote'" <amitlangote09(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: speeding up planning with partitions
Date: 2019-03-05 10:25:13
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On 2019/03/04 19:38, Amit Langote wrote:
> 2. Defer inheritance expansion to add_other_rels_to_query(). Although the
> purpose of doing this is to perform partition pruning before adding the
> children, this patch doesn't change when the pruning occurs. It deals
> with other issues that must be taken care of due to adding children during
> query_planner instead of during subquery_planner. Especially,
> inheritance_planner now has to add the child target relations on its own.
> Also, delaying adding children also affects adding junk columns to the
> query's targetlist based on PlanRowMarks, because preprocess_targetlist
> can no longer finalize which junk columns to add for a "parent"
> PlanRowMark; that must be delayed until all child PlanRowMarks are added
> and their allMarkTypes propagated to the parent PlanRowMark.

I thought more on this and started wondering why we can't call
preprocess_targetlist() from query_planner() instead of from
grouping_planner()? We don't have to treat parent row marks specially if
preprocess_targetlist() is called after adding other rels (and hence all
child row marks). This will change the order in which expressions are
added to baserels targetlists and hence the order of expressions in their
Path's targetlist, because the expressions contained in targetlist
(including RETURNING) and other junk expressions will be added after
expressions referenced in WHERE clauses, whereas the order is reverse
today. But if we do what we propose above, the order will be uniform for
all cases, that is, not one for regular table baserels and another for
inherited table baserels.



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