optimizer cost calculation problem

Kenji Sugita has identified a problem with cost_sort() in costsize.c.

In the following code fragment, sortmembytes is defined as long. So

double nruns = nbytes / (sortmembytes * 2);

may cause an integer overflow if sortmembytes exceeds 2^30, which in
turn make optimizer to produce wrong query plan(this actually happned
in a large PostgreSQL installation which has tons of memory). Here is a
proposed fix against current:

*** optimizer/path/costsize.c 16 Feb 2003 02:30:38 -0000 1.107
--- optimizer/path/costsize.c 31 Mar 2003 22:25:06 -0000
***************
*** 490,496 ****
Cost startup_cost = input_cost;
Cost run_cost = 0;
double nbytes = relation_byte_size(tuples, width);
! long sortmembytes = SortMem * 1024L;

if (!enable_sort)
startup_cost += disable_cost;
--- 490,496 ----
Cost startup_cost = input_cost;
Cost run_cost = 0;
double nbytes = relation_byte_size(tuples, width);
! double sortmembytes = SortMem * 1024.0;

if (!enable_sort)
startup_cost += disable_cost;