Re: Keep notnullattrs in RelOptInfo (Was part of UniqueKey patch series)

I assume we want to know if a Var is nullable with a function like. 

is_var_notnullable(Var *var,  Relids relids).  If so, we can define the data as below:

struct RelOptInfo {

Bitmapset** notnullattrs;
..

}; 

After this we can implement the function as: 

bool
is_var_notnullable(Var* var, Relids relids)
{
  RelOptInfo *rel = find_rel_by_relids(reldis);
  return bms_is_member(var->varattno, rel->notnullattrs[var->varno]);
}

Probably we can make some hackers to reduce the notnullattrs's memory usage
overhead.