| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Corey Huinker <corey(dot)huinker(at)gmail(dot)com> |
| Subject: | Re: Parallel tuplesort (for parallel B-Tree index creation) |
| Date: | 2016-09-07 05:40:20 |
| Message-ID: | CAM3SWZRzX_HB_yJ7phou4sS07MRgKWXPJxJLxSUiFjEztHa_4Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Sep 6, 2016 at 10:36 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> Well, maybe, but the whole idea behind replacement_sort_tuples (by
> which I mean the continued occasional use of replacement selection by
> Postgres) was that we hope to avoid a merge step *entirely*. This new
> merge shift down heap patch could make the merge step so cheap as to
> be next to free anyway (in the even of presorted input)
I mean: Cheaper than just processing the tuples to return to caller
without comparisons/merging (within the TSS_SORTEDONTAPE path). I do
not mean free in an absolute sense, of course.
--
Peter Geoghegan
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