Change class variable names in rowid_filter to longer, more clear names

No code logic changes was done

a     -> gain
b     -> cost_of_building_range_filter
a_adj -> gain_adj
r     -> row_combinations

Other things:
- Optimized the layout of class Range_rowid_filter_cost_info.
  One effect was that I moved key_no to the private section to get
  better alignment and had to introduce a get_key_no() function.
- Indentation changes in rowid_filter.cc to avoid long rows.

sql/opt_trace.cc

@@ -692,7 +692,7 @@ void print_best_access_for_table(THD *thd, POSITION *pos,
   obj.add("uses_join_buffering", pos->use_join_buffer);
   if (pos->range_rowid_filter_info)
   {
-    uint key_no= pos->range_rowid_filter_info->key_no;
+    uint key_no= pos->range_rowid_filter_info->get_key_no();
     obj.add("rowid_filter_key",
             pos->table->table->key_info[key_no].name);
   }

sql/rowid_filter.cc

@@ -24,8 +24,8 @@
 
 
 inline
-double Range_rowid_filter_cost_info::lookup_cost(
-                                     Rowid_filter_container_type cont_type)
+double Range_rowid_filter_cost_info::
+lookup_cost(Rowid_filter_container_type cont_type)
 {
   switch (cont_type) {
   case SORTED_ARRAY_CONTAINER:
@@ -44,8 +44,8 @@ double Range_rowid_filter_cost_info::lookup_cost(
 */
 
 inline
-double Range_rowid_filter_cost_info::avg_access_and_eval_gain_per_row(
-                                     Rowid_filter_container_type cont_type)
+double Range_rowid_filter_cost_info::
+avg_access_and_eval_gain_per_row(Rowid_filter_container_type cont_type)
 {
   return (1+1.0/TIME_FOR_COMPARE) * (1 - selectivity) -
          lookup_cost(cont_type);
@@ -76,10 +76,11 @@ double Range_rowid_filter_cost_info::avg_access_and_eval_gain_per_row(
 */
 
 inline
-double Range_rowid_filter_cost_info::avg_adjusted_gain_per_row(
-				         double access_cost_factor)
+double Range_rowid_filter_cost_info::
+avg_adjusted_gain_per_row(double access_cost_factor)
 {
-  return a - (1 - access_cost_factor) * (1 - selectivity);
+  DBUG_ASSERT(access_cost_factor >= 0.0 && access_cost_factor <= 1.0);
+  return gain - (1 - access_cost_factor) * (1 - selectivity);
 }
 
 
@@ -93,10 +94,11 @@ double Range_rowid_filter_cost_info::avg_adjusted_gain_per_row(
 */
 
 inline void
-Range_rowid_filter_cost_info::set_adjusted_gain_param(double access_cost_factor)
+Range_rowid_filter_cost_info::
+set_adjusted_gain_param(double access_cost_factor)
 {
-  a_adj= avg_adjusted_gain_per_row(access_cost_factor);
-  cross_x_adj= b / a_adj;
+  gain_adj= avg_adjusted_gain_per_row(access_cost_factor);
+  cross_x_adj= cost_of_building_range_filter / gain_adj;
 }
 
 
@@ -118,13 +120,13 @@ void Range_rowid_filter_cost_info::init(Rowid_filter_container_type cont_type,
   table= tab;
   key_no= idx;
   est_elements= (ulonglong) table->opt_range[key_no].rows;
-  b= build_cost(container_type);
+  cost_of_building_range_filter= build_cost(container_type);
   selectivity= est_elements/((double) table->stat_records());
-  a= avg_access_and_eval_gain_per_row(container_type);
-  if (a > 0)
-    cross_x= b/a;
+  gain= avg_access_and_eval_gain_per_row(container_type);
+  if (gain > 0)
+    cross_x= cost_of_building_range_filter/gain;
   else
-    cross_x= b+1;
+    cross_x= cost_of_building_range_filter+1;
   abs_independent.clear_all();
 }
 
@@ -179,7 +181,7 @@ int compare_range_rowid_filter_cost_info_by_a(
                         Range_rowid_filter_cost_info **filter_ptr_1,
                         Range_rowid_filter_cost_info **filter_ptr_2)
 {
-  double diff= (*filter_ptr_2)->get_a() - (*filter_ptr_1)->get_a();
+  double diff= (*filter_ptr_2)->get_gain() - (*filter_ptr_1)->get_gain();
   return (diff < 0 ? -1 : (diff > 0 ? 1 : 0));
 }
 
@@ -206,7 +208,8 @@ void TABLE::prune_range_rowid_filters()
     the elements if this bit matrix.
   */
 
-  Range_rowid_filter_cost_info **filter_ptr_1= range_rowid_filter_cost_info_ptr;
+  Range_rowid_filter_cost_info **filter_ptr_1=
+    range_rowid_filter_cost_info_ptr;
   for (uint i= 0;
        i < range_rowid_filter_cost_info_elems;
        i++, filter_ptr_1++)
@@ -245,7 +248,7 @@ void TABLE::prune_range_rowid_filters()
   */
 
   Range_rowid_filter_cost_info **cand_filter_ptr=
-                                   range_rowid_filter_cost_info_ptr;
+    range_rowid_filter_cost_info_ptr;
   for (uint i= 0;
        i < range_rowid_filter_cost_info_elems;
        i++, cand_filter_ptr++)
@@ -439,7 +442,7 @@ void Range_rowid_filter_cost_info::trace_info(THD *thd)
 {
   Json_writer_object js_obj(thd);
   js_obj.add("key", table->key_info[key_no].name);
-  js_obj.add("build_cost", b);
+  js_obj.add("build_cost", cost_of_building_range_filter);
   js_obj.add("rows", est_elements);
 }
 

sql/rowid_filter.h

@@ -396,14 +396,16 @@ class Range_rowid_filter_cost_info : public Sql_alloc
   TABLE *table;
   /* Estimated number of elements in the filter */
   ulonglong est_elements;
-  /* The cost of building the range filter */
-  double b;
+  /* The index whose range scan would be used to build the range filter */
+  uint key_no;
+  double cost_of_building_range_filter;
   /*
-     a*N-b yields the gain of the filter
-     for N key tuples of the index key_no
+     (gain*row_combinations)-cost_of_building_range_filter yields the gain of
+     the filter for 'row_combinations' key tuples of the index key_no
+     calculated with avg_access_and_eval_gain_per_row(container_type);
   */
-  double a;
-  /* The value of N where the gain is  0 */
+  double gain;
+  /* The value of row_combinations where the gain is 0 */
   double cross_x;
   /* Used for pruning of the potential range filters */
   key_map abs_independent;
@@ -412,16 +414,14 @@ class Range_rowid_filter_cost_info : public Sql_alloc
     These two parameters are used to choose the best range filter
     in the function TABLE::best_range_rowid_filter_for_partial_join
   */
-  double a_adj;
+  double gain_adj;
   double cross_x_adj;
 
 public:
-  /* The type of the container of the range filter */
-  Rowid_filter_container_type container_type;
-  /* The index whose range scan would be used to build the range filter */
-  uint key_no;
   /* The selectivity of the range filter */
   double selectivity;
+  /* The type of the container of the range filter */
+  Rowid_filter_container_type container_type;
 
   Range_rowid_filter_cost_info() : table(0), key_no(0) {}
 
@@ -440,29 +440,30 @@ class Range_rowid_filter_cost_info : public Sql_alloc
   inline void set_adjusted_gain_param(double access_cost_factor);
 
   /* Get the gain that usage of filter promises for r key tuples */
-  inline double get_gain(double r)
+  inline double get_gain(double row_combinations)
   {
-    return r * a - b;
+    return row_combinations * gain - cost_of_building_range_filter;
   }
 
   /* Get the adjusted gain that usage of filter promises for r key tuples */
-  inline double get_adjusted_gain(double r)
+  inline double get_adjusted_gain(double row_combinations)
   {
-    return r * a_adj - b;
+    return row_combinations * gain_adj - cost_of_building_range_filter;
   }
 
   /*
     The gain promised by usage of the filter for r key tuples
     due to less condition evaluations
   */
-  inline double get_cmp_gain(double r)
+  inline double get_cmp_gain(double row_combinations)
   {
-    return r * (1 - selectivity) / TIME_FOR_COMPARE;
+    return row_combinations * (1 - selectivity) / TIME_FOR_COMPARE;
   }
 
   Rowid_filter_container *create_container();
 
-  double get_a() { return a; }
+  double get_gain() { return gain; }
+  uint get_key_no() { return key_no; }
 
   void trace_info(THD *thd);
 

sql/sql_select.cc

@@ -1917,9 +1917,9 @@ bool JOIN::make_range_rowid_filters()
       continue;
 
     DBUG_ASSERT(!(tab->ref.key >= 0 &&
-                  tab->ref.key == (int) tab->range_rowid_filter_info->key_no));
+                  tab->ref.key == (int) tab->range_rowid_filter_info->get_key_no()));
     DBUG_ASSERT(!(tab->ref.key == -1 && tab->quick &&
-                  tab->quick->index == tab->range_rowid_filter_info->key_no));
+                  tab->quick->index == tab->range_rowid_filter_info->get_key_no()));
 
     int err;
     SQL_SELECT *sel= NULL;
@@ -1932,7 +1932,7 @@ bool JOIN::make_range_rowid_filters()
 
     key_map filter_map;
     filter_map.clear_all();
-    filter_map.set_bit(tab->range_rowid_filter_info->key_no);
+    filter_map.set_bit(tab->range_rowid_filter_info->get_key_no());
     filter_map.merge(tab->table->with_impossible_ranges);
     bool force_index_save= tab->table->force_index;
     tab->table->force_index= true;
@@ -8429,7 +8429,7 @@ best_access_path(JOIN      *join,
             tmp-= filter->get_adjusted_gain(rows) - filter->get_cmp_gain(rows);
             DBUG_ASSERT(tmp >= 0);
             trace_access_idx.add("rowid_filter_key",
-                                 table->key_info[filter->key_no].name);
+                                 table->key_info[filter->get_key_no()].name);
           }
         }
       }