Re: PoC: Partial sort

Hi,

On 10/20/2015 01:17 PM, Alexander Korotkov wrote:
> On Fri, Oct 16, 2015 at 7:11 PM, Alexander Korotkov
> <aekorotkov(at)gmail(dot)com <mailto:aekorotkov(at)gmail(dot)com>> wrote:
>
> On Sun, Jun 7, 2015 at 11:01 PM, Peter Geoghegan <pg(at)heroku(dot)com
> <mailto:pg(at)heroku(dot)com>> wrote:
>
> On Sun, Jun 7, 2015 at 8:10 AM, Andreas Karlsson
> <andreas(at)proxel(dot)se <mailto:andreas(at)proxel(dot)se>> wrote:
> > Are you planning to work on this patch for 9.6?
>
> FWIW I hope so. It's a nice patch.
>
>
> I'm trying to to whisk dust. Rebased version of patch is attached.
> This patch isn't passing regression tests because of plan changes.
> I'm not yet sure about those changes: why they happens and are they
> really regression?
> Since I'm not very familiar with planning of INSERT ON CONFLICT and
> RLS, any help is appreciated.
>
>
> Planner regression is fixed in the attached version of patch. It appears
> that get_cheapest_fractional_path_for_pathkeys() behaved wrong when no
> ordering is required.
>

Alexander, are you working on this patch? I'd like to look at the patch,
but the last available version (v4) no longer applies - there's plenty
of bitrot. Do you plan to send an updated / rebased version?

The main thing I'm particularly interested in is how much is this
coupled with the Sort node, and whether it's possible to feed partially
sorted tuples into other nodes.

I'm particularly thinking about Hash Aggregate, because the partial sort
allows to keep only the "current group" in a hash table, making it much
more memory efficient / faster. What do you think?

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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