Split cost calculations into fetch and total

This patch causes no changes in costs or result files.

Changes:
- Store row compare cost separately in Cost_estimate::comp_cost
- Store cost of fetching rows separately in OPT_RANGE
- Use range->fetch_cost instead of adjust_quick_cost(total_cost)

This was done to simplify cost calculation in sql_select.cc:
- We can use range->fetch_cost directly without having to call
  adjust_quick_cost(). adjust_quick_cost() is now removed.

Other things:
- Removed some not used functions in Cost_estimate

sql/handler.h

@@ -2786,6 +2786,7 @@ public:
   double cpu_cost;        /* total cost of operations in CPU               */
   double idx_cpu_cost;    /* cost of operations in CPU for index           */
   double import_cost;     /* cost of remote operations     */
+  double comp_cost;       /* Cost of comparing found rows with WHERE clause */
   double mem_cost;        /* cost of used memory           */
 
   static constexpr double IO_COEFF= 1;
@@ -2799,6 +2800,15 @@ public:
   }
 
   double total_cost() const
+  {
+    return IO_COEFF*io_count*avg_io_cost +
+           IO_COEFF*idx_io_count*idx_avg_io_cost +
+           CPU_COEFF*(cpu_cost + idx_cpu_cost + comp_cost) +
+           MEM_COEFF*mem_cost + IMPORT_COEFF*import_cost;
+  }
+
+  /* Cost of fetching a row */
+  double fetch_cost() const
   {
     return IO_COEFF*io_count*avg_io_cost +
            IO_COEFF*idx_io_count*idx_avg_io_cost +
@@ -2806,6 +2816,16 @@ public:
            MEM_COEFF*mem_cost + IMPORT_COEFF*import_cost;
   }
 
+  /*
+    Cost of comparing the row with the WHERE clause
+    Note that fetch_cost() + compare_cost() == total_cost()
+  */
+  double compare_cost() const
+  {
+    return CPU_COEFF*comp_cost;
+  }
+
+
   double index_only_cost()
   {
     return IO_COEFF*idx_io_count*idx_avg_io_cost +
@@ -2820,14 +2840,15 @@ public:
   bool is_zero() const
   {
     return io_count == 0.0 && idx_io_count == 0.0 && cpu_cost == 0.0 &&
-      import_cost == 0.0 && mem_cost == 0.0;
+      import_cost == 0.0 && mem_cost == 0.0 && comp_cost;
   }
 
   void reset()
   {
     avg_io_cost= 1.0;
     idx_avg_io_cost= 1.0;
-    io_count= idx_io_count= cpu_cost= idx_cpu_cost= mem_cost= import_cost= 0.0;
+    io_count= idx_io_count= cpu_cost= idx_cpu_cost= mem_cost= import_cost=
+      comp_cost= 0.0;
   }
 
   void multiply(double m)
@@ -2837,6 +2858,7 @@ public:
     idx_io_count *= m;
     idx_cpu_cost *= m;
     import_cost *= m;
+    comp_cost *= m;
     /* Don't multiply mem_cost */
   }
 
@@ -2861,6 +2883,7 @@ public:
     cpu_cost += cost->cpu_cost;
     idx_cpu_cost += cost->idx_cpu_cost;
     import_cost += cost->import_cost;
+    comp_cost+= cost->comp_cost;
   }
 
   void add_io(double add_io_cnt, double add_avg_cost)
@@ -2875,15 +2898,6 @@ public:
     }
   }
 
-  /// Add to CPU cost
-  void add_cpu(double add_cpu_cost) { cpu_cost+= add_cpu_cost; }
-
-  /// Add to import cost
-  void add_import(double add_import_cost) { import_cost+= add_import_cost; }
-
-  /// Add to memory cost
-  void add_mem(double add_mem_cost) { mem_cost+= add_mem_cost; }
-
   /*
     To be used when we go from old single value-based cost calculations to
     the new Cost_estimate-based.

sql/multi_range_read.cc

@@ -327,15 +327,18 @@ handler::multi_range_read_info_const(uint keyno, RANGE_SEQ_IF *seq,
       uint limited_ranges= (uint) MY_MIN((ulonglong) n_ranges, io_blocks);
       cost->cpu_cost= read_time(keyno, limited_ranges, total_rows);
     }
-    cost->cpu_cost+= (rows2double(total_rows) / TIME_FOR_COMPARE +
+    cost->comp_cost= (rows2double(total_rows) / TIME_FOR_COMPARE +
                       MULTI_RANGE_READ_SETUP_COST);
   }
   DBUG_PRINT("statistics",
              ("key: %s  rows: %llu  total_cost: %.3f  io_blocks: %llu  "
-              "idx_io_count: %.3f  cpu_cost: %.3f  io_count: %.3f",
+              "idx_io_count: %.3f  cpu_cost: %.3f  io_count: %.3f  "
+              "compare_cost: %.3f",
               table->s->keynames.type_names[keyno],
-              (ulonglong) total_rows, cost->total_cost(), (ulonglong) io_blocks,
-              cost->idx_io_count, cost->cpu_cost, cost->io_count));
+              (ulonglong) total_rows, cost->total_cost(),
+              (ulonglong) io_blocks,
+              cost->idx_io_count, cost->cpu_cost, cost->io_count,
+              cost->comp_cost));
   DBUG_RETURN(total_rows);
 }
 
@@ -407,7 +410,7 @@ ha_rows handler::multi_range_read_info(uint keyno, uint n_ranges, uint n_rows,
   {
     cost->cpu_cost= read_time(keyno, n_ranges, (uint)n_rows);
   }
-  cost->cpu_cost+= rows2double(n_rows) / TIME_FOR_COMPARE;
+  cost->comp_cost= rows2double(n_rows) / TIME_FOR_COMPARE;
   return 0;
 }
 

sql/opt_range.cc

@@ -11776,7 +11776,9 @@ ha_rows check_quick_select(PARAM *param, uint idx, bool index_only,
       param->table->opt_range_condition_rows=
         MY_MIN(param->table->opt_range_condition_rows, rows);
       range->rows= rows;
-      range->cost= cost->total_cost();
+      range->fetch_cost= cost->fetch_cost();
+      /* Same as total cost */
+      range->cost= range->fetch_cost + cost->compare_cost();
       if (param->table->file->is_clustering_key(keynr))
 	range->index_only_cost= 0;
       else

sql/sql_select.cc

@@ -7675,26 +7675,6 @@ double cost_for_index_read(const THD *thd, const TABLE *table, uint key,
 }
 
 
-/*
-  Adjust cost from table->quick_costs calculated by
-  multi_range_read_info_const() to be comparable with cost_for_index_read()
-
-  This functions is needed because best_access_path doesn't add
-  TIME_FOR_COMPARE to it's costs until very late.
-  Preferably we should fix so that all costs are comparably.
-  (All compared costs should include TIME_FOR_COMPARE for all found
-  rows).
-*/
-
-double adjust_quick_cost(double quick_cost, ha_rows records)
-{
-  double cost= (quick_cost - MULTI_RANGE_READ_SETUP_COST -
-                rows2double(records)/TIME_FOR_COMPARE);
-  DBUG_ASSERT(cost > 0.0);
-  return cost;
-}
-
-
 /**
   Find the best access path for an extension of a partial execution
   plan and add this path to the plan.
@@ -7938,7 +7918,7 @@ best_access_path(JOIN      *join,
                 add("access_type", join_type_str[type]).
                 add("index", keyinfo->name);
             if (!found_ref && table->opt_range_keys.is_set(key))
-              tmp= adjust_quick_cost(table->opt_range[key].cost, 1);
+              tmp= table->opt_range[key].fetch_cost;
             else
               tmp= table->file->avg_io_cost();
             /*
@@ -7979,8 +7959,7 @@ best_access_path(JOIN      *join,
               {
                 records= (double) table->opt_range[key].rows;
                 trace_access_idx.add("used_range_estimates", true);
-                tmp= adjust_quick_cost(table->opt_range[key].cost,
-                                       table->opt_range[key].rows);
+                tmp= table->opt_range[key].fetch_cost;
                 goto got_cost2;
               }
               /* quick_range couldn't use key! */
@@ -8106,8 +8085,7 @@ best_access_path(JOIN      *join,
                 table->opt_range[key].ranges == 1 + MY_TEST(ref_or_null_part)) //(C3)
             {
               records= (double) table->opt_range[key].rows;
-              tmp= adjust_quick_cost(table->opt_range[key].cost,
-                                     table->opt_range[key].rows);
+              tmp= table->opt_range[key].fetch_cost;
               trace_access_idx.add("used_range_estimates", true);
               goto got_cost2;
             }

sql/table.h

@@ -1356,7 +1356,10 @@ public:
     uint        key_parts;
     uint        ranges;
     ha_rows     rows;
+    /* Cost of fetching and comparing the row aginst the WHERE clause */
     double      cost;
+    /* Cost of comparing row with WHERE clause. Included in 'cost' */
+    double      fetch_cost;
     /*
       If there is a range access by i-th index then the cost of
       index only access for it is stored in index_only_costs[i]