remove SHOW_OPTIMIZER_COST

avoid contaminating SHOW code with sysvar implementation details.
And no hard-coded factor either.

sql/item_func.cc

@@ -5920,7 +5920,6 @@ bool Item_func_get_system_var::fix_length_and_dec(THD *thd)
       decimals=0;
       break;
     case SHOW_DOUBLE:
-    case SHOW_OPTIMIZER_COST:
       decimals= 6;
       collation= DTCollation_numeric();
       fix_char_length(DBL_DIG + 6);
@@ -5978,7 +5977,6 @@ const Type_handler *Item_func_get_system_var::type_handler() const
     case SHOW_CHAR_PTR: 
     case SHOW_LEX_STRING:
       return &type_handler_varchar;
-    case SHOW_OPTIMIZER_COST:
     case SHOW_DOUBLE:
       return &type_handler_double;
     default:

sql/set_var.cc

@@ -310,13 +310,7 @@ do {                                                \
     case SHOW_HA_ROWS:  do_num_val (ha_rows,CMD);
 
 #define case_for_double(CMD)                        \
-    case SHOW_DOUBLE:   do_num_val (double,CMD);    \
-    case SHOW_OPTIMIZER_COST:                       \
-    {                                               \
-      double val= ((*(double*) value) == OPTIMIZER_COST_UNDEF ? OPTIMIZER_COST_UNDEF : \
-                   (*(double*) value) * 1000);      \
-      CMD;                                          \
-    } while (0)
+    case SHOW_DOUBLE:   do_num_val (double,CMD);
 
 #define case_get_string_as_lex_string               \
     case SHOW_CHAR:                                 \

sql/sql_plugin.h

@@ -24,7 +24,6 @@
 #define SHOW_always_last SHOW_KEY_CACHE_LONG, \
             SHOW_HAVE, SHOW_MY_BOOL, SHOW_HA_ROWS, SHOW_SYS, \
             SHOW_LONG_NOFLUSH, SHOW_LEX_STRING, SHOW_ATOMIC_COUNTER_UINT32_T, \
-            SHOW_OPTIMIZER_COST, \
       /* SHOW_*_STATUS must be at the end, SHOW_LONG_STATUS being first */ \
             SHOW_LONG_STATUS, SHOW_DOUBLE_STATUS, SHOW_LONGLONG_STATUS, \
             SHOW_UINT32_STATUS

sql/sql_show.cc

@@ -3669,9 +3669,6 @@ const char* get_one_variable(THD *thd,
     /* 6 is the default precision for '%f' in sprintf() */
     end= buff + my_fcvt(*value.as_double, 6, buff, NULL);
     break;
-  case SHOW_OPTIMIZER_COST:                 // Stored in 1ms, displayed in us
-    end= buff + my_fcvt(*value.as_double*1000, 6, buff, NULL);
-    break;
   case SHOW_LONG_STATUS:
     value.as_char= status_var_value.as_char + value.as_intptr;
     /* fall through */

sql/sys_vars.inl

@@ -1257,10 +1257,7 @@ class Sys_var_optimizer_cost: public Sys_var_double
                    substitute)
   {
     if (arg_cost_adjust == 1000)
-    {
-      show_val_type= SHOW_OPTIMIZER_COST;     // For select @@var
       option.var_type|= GET_ADJUST_VALUE;
-    }
     cost_adjust= (double) arg_cost_adjust;
   }
   bool session_update(THD *thd, set_var *var)
@@ -1281,6 +1278,22 @@ class Sys_var_optimizer_cost: public Sys_var_double
     var->save_result.double_value= getopt_ulonglong2double(option.def_value)*
       cost_adjust;
   }
+  const uchar *tmp_ptr(THD *thd) const
+  {
+    if (thd->sys_var_tmp.double_value > 0)
+      thd->sys_var_tmp.double_value*= cost_adjust;
+    return (uchar*) &thd->sys_var_tmp.double_value;
+  }
+  const uchar *session_value_ptr(THD *thd, const LEX_CSTRING *base) const
+  {
+    thd->sys_var_tmp.double_value= session_var(thd, double);
+    return tmp_ptr(thd);
+  }
+  const uchar *global_value_ptr(THD *thd, const LEX_CSTRING *base) const
+  {
+    thd->sys_var_tmp.double_value= global_var(double);
+    return tmp_ptr(thd);
+  }
 };
 
 
@@ -1360,7 +1373,8 @@ class Sys_var_engine_optimizer_cost: public Sys_var_optimizer_cost
     OPTIMIZER_COSTS *optimizer_costs= get_optimizer_costs(base);
     if (!optimizer_costs)
       optimizer_costs= &default_optimizer_costs;
-    return cost_var_ptr(optimizer_costs, offset);
+    thd->sys_var_tmp.double_value= cost_var(optimizer_costs, offset);
+    return tmp_ptr(thd);
   }
 };