Re: PoC: Partial sort - Mailing list pgsql-hackers

From Alexander Korotkov
Subject Re: PoC: Partial sort
Date
Msg-id CAPpHfdtuwi4CaAXAfw_-yzq5yU_v0asTub1gYyaeQwAmV08Z1w@mail.gmail.com
Whole thread Raw
In response to Re: PoC: Partial sort  (Marti Raudsepp <marti@juffo.org>)
Responses Re: PoC: Partial sort  (Marti Raudsepp <marti@juffo.org>)
Re: PoC: Partial sort  (Marti Raudsepp <marti@juffo.org>)
List pgsql-hackers
On Tue, Jan 28, 2014 at 7:41 AM, Marti Raudsepp <marti@juffo.org> wrote:
On Mon, Jan 27, 2014 at 9:26 PM, Alexander Korotkov
<aekorotkov@gmail.com> wrote:
> For now, I have attempt to fix extra columns in mergejoin problem. It would
> be nice if you test it.

Yes, it solves the test cases I was trying with, thanks.

> 1) With enable_partialsort = off all mergejoin logic should behave as
> without partial sort patch.
> 2) With partial sort patch get_cheapest_fractional_path_for_pathkeys
> function is much more expensive to execute. With enable_partialsort = off it
> should be as cheap as without partial sort patch.

When it comes to planning time, I really don't think you should
bother. The planner enable_* settings are meant for troubleshooting,
debugging and learning about the planner. You should not expect people
to disable them in a production setting. It's not worth complicating
the code for that rare case.

This is stated in the documentation
(http://www.postgresql.org/docs/current/static/runtime-config-query.html)
and repeatedly on the mailing lists.

But some benchmarks of planning performance are certainly warranted.

I didn't test it, but I worry that overhead might be high.
If it's true then it could be like constraint_exclusion option which id off by default because of planning overhead.

------
With best regards,
Alexander Korotkov.

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