| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Rethinking representation of partial-aggregate steps |
| Date: | 2016-06-23 17:49:55 |
| Message-ID: | CANP8+jJcxwGifuy+3ojjLOppNC=wSCLf88NLG8DzZA9-Mt_8QA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 23 June 2016 at 18:31, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> Sure, but aggregating as early as possible will often have the effect
> of dramatically reducing the number of tuples that have to pass
> through upper levels of the plan tree, which seems it would frequently
> far outweigh those considerations.
>
Agreed
I can imagine plans where a useful aggregation occurs before every join, so
N > 2 is easily possible.
--
Simon Riggs http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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