In 5.0, Field_double::val_str uses "%g" to render floating point

numbers, which uses "X.YeZ" notation when the exponent Z would be
less than -4. That behavior at -4 is not exactly what we want, and
our Decimal type offers smarter number representation.  By changing
profiling to use Decimal types, we get more readable output.


sql/sql_profile.cc:
  Change the DOUBLE I_S types to DECIMAL, so we get a smarter
  floating-point number renderer.
sql/sql_show.cc:
  Add MYSQL_TYPE_DECIMAL as a string-ish type that INFORMATION_SCHEMA
  tables may use.

sql/sql_profile.cc

@@ -44,9 +44,9 @@ ST_FIELD_INFO query_profile_statistics_info[]=
   {"QUERY_ID", 20, MYSQL_TYPE_LONG, 0, false, "Query_id"},
   {"SEQ", 20, MYSQL_TYPE_LONG, 0, false, "Seq"},
   {"STATE", 30, MYSQL_TYPE_STRING, 0, false, "Status"},
-  {"DURATION", TIME_FLOAT_DIGITS, MYSQL_TYPE_DOUBLE, 0, false, "Duration"},
-  {"CPU_USER", TIME_FLOAT_DIGITS, MYSQL_TYPE_DOUBLE, 0, true, "CPU_user"},
-  {"CPU_SYSTEM", TIME_FLOAT_DIGITS, MYSQL_TYPE_DOUBLE, 0, true, "CPU_system"},
+  {"DURATION", TIME_FLOAT_DIGITS, MYSQL_TYPE_DECIMAL, 0, false, "Duration"},
+  {"CPU_USER", TIME_FLOAT_DIGITS, MYSQL_TYPE_DECIMAL, 0, true, "CPU_user"},
+  {"CPU_SYSTEM", TIME_FLOAT_DIGITS, MYSQL_TYPE_DECIMAL, 0, true, "CPU_system"},
   {"CONTEXT_VOLUNTARY", 20, MYSQL_TYPE_LONG, 0, true, "Context_voluntary"},
   {"CONTEXT_INVOLUNTARY", 20, MYSQL_TYPE_LONG, 0, true, "Context_involuntary"},
   {"BLOCK_OPS_IN", 20, MYSQL_TYPE_LONG, 0, true, "Block_ops_in"},
@@ -557,16 +557,31 @@ int PROFILING::fill_statistics_info(THD *thd, struct st_table_list *tables, Item
       */
       table->field[2]->store(previous->status, strlen(previous->status), 
                              system_charset_info);
-      table->field[3]->store((double)(entry->time_usecs - 
-                             previous->time_usecs)/(1000*1000));
+
+      my_decimal duration;
+      double2my_decimal(E_DEC_FATAL_ERROR, 
+                        (entry->time_usecs-previous->time_usecs)/(1000.0*1000),
+                        &duration);
+      table->field[3]->store_decimal(&duration);
 
 #ifdef HAVE_GETRUSAGE
-      table->field[4]->store((double)RUSAGE_DIFF_USEC(entry->rusage.ru_utime,
-                             previous->rusage.ru_utime)/(1000.0*1000));
-      table->field[4]->set_notnull();
-      table->field[5]->store((double)RUSAGE_DIFF_USEC(entry->rusage.ru_stime,
-                             previous->rusage.ru_stime)/(1000.0*1000));
 
+      my_decimal cpu_utime, cpu_stime;
+      double2my_decimal(E_DEC_FATAL_ERROR, 
+                        RUSAGE_DIFF_USEC(entry->rusage.ru_utime, 
+                                         previous->rusage.ru_utime) /
+                                                        (1000.0*1000),
+                        &cpu_utime);
+
+      double2my_decimal(E_DEC_FATAL_ERROR, 
+                        RUSAGE_DIFF_USEC(entry->rusage.ru_stime,
+                                         previous->rusage.ru_stime) / 
+                                                        (1000.0*1000),
+                        &cpu_stime);
+
+      table->field[4]->store_decimal(&cpu_utime);
+      table->field[5]->store_decimal(&cpu_stime);
+      table->field[4]->set_notnull();
       table->field[5]->set_notnull();
 #else
       /* TODO: Add CPU-usage info for non-BSD systems */

sql/sql_show.cc

@@ -3657,11 +3657,18 @@ TABLE *create_schema_table(THD *thd, TABLE_LIST *table_list)
                            fields_info->field_length)) == NULL)
         DBUG_RETURN(NULL);
       break;
+    case MYSQL_TYPE_DECIMAL:
+    case MYSQL_TYPE_STRING:
     default:
       /* Don't let unimplemented types pass through. Could be a grave error. */
-      DBUG_ASSERT(fields_info->field_type == MYSQL_TYPE_STRING);
+      DBUG_ASSERT(fields_info->field_type == MYSQL_TYPE_STRING ||
+                  fields_info->field_type == MYSQL_TYPE_DECIMAL);
 
-      /* this should be changed when Item_empty_string is fixed(in 4.1) */
+      /** 
+        @todo  Change when Item_empty_string is fixed (in 4.1).  [Presumably, 
+        this means removing the first of two steps:  setting a useless, bogus
+        value; and then setting the attributes.]
+      */
       if (!(item= new Item_empty_string("", 0, cs)))
       {
         DBUG_RETURN(0);