Re: PoC: Partial sort

On Tue, Jan 28, 2014 at 7:41 AM, Marti Raudsepp <marti(at)juffo(dot)org> wrote:

> On Mon, Jan 27, 2014 at 9:26 PM, Alexander Korotkov
> <aekorotkov(at)gmail(dot)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.