Re: cost_sort() improvements

Peter Geoghegan wrote:
> On Thu, Jun 28, 2018 at 9:47 AM, Teodor Sigaev <teodor(at)sigaev(dot)ru> wrote:
>> Current estimation of sort cost has following issues:
>> - it doesn't differ one and many columns sort
>> - it doesn't pay attention to comparison function cost and column width
>> - it doesn't try to count number of calls of comparison function on per
>> column
>> basis
>
> I've been suspicious of the arbitrary way in which I/O for external
> sorts is costed by cost_sort() for a long time. I'm not 100% sure
> about how we should think about this question, but I am sure that it
> needs to be improved in *some* way.
Agree, but I think it should be separated patch to attack this issue. And I
don't have an idea how to do it, at least right now. Nevertheless, I hope, issue
of estimation of disk-based sort isn't a blocker of CPU cost estimation
improvements.

--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/