Re: FETCH FIRST clause WITH TIES option

[Tomas Vondra]

Hi,

Unfortunately this got broken again, this time by aef65db676 :-(

I've tried to fix the merge conflict (essentially by moving some of the
code to adjust_limit_rows_costs(), but I'm wondering if the code added to
create_limit_path is actually correct

   if (count_est != 0)
   {
       double        count_rows;

       if (count_est > 0)
           count_rows = (double) count_est;
       else
           count_rows = clamp_row_est(subpath->rows * 0.10);

       if (limitOption == WITH_TIES)
       {
           ...
           count_rows = Max(avgGroupSize, count_est + (...));
       }
       ...
   }

Firstly, this seriously needs some comment explaining why we do this. But
more importantly - shouldn't it really be

   count_rows = Max(avgGroupSize, count_rows + (...));

instead of using count_est again (which might easily be -1 anyway)?


regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services