On Fri, Nov 20, 2015 at 12:54 AM, Peter Geoghegan <pg@heroku.com> wrote:
> * One run can be created with replacement selection, where a
> hyrbid-sort merge strategy needs to create and then merge many runs.
> When I started work on this patch, I was pretty sure that case would
> be noticeably regressed. I was wrong.
Hm. Have you tested a nearly-sorted input set around 1.5x the size of
work_mem? That should produce a single run using the heap to generate
runs but generate two runs if, AIUI, you're just filling work_mem,
running quicksort, dumping that run entirely and starting fresh.
I don't mean to say it's representative but if you're looking for a
worst case...
--
greg