BUG#12427262 : 60961: SHOW TABLES VERY SLOW WHEN NOT IN SYSTEM DISK CACHE

Reason:
 This is a regression happened because of changes done in code refactoring 
 in 5.1 from 5.0.

Issue: 
 While doing "Show tables" lex->verbose was being checked to avoid opening
 FRM files to get table type. In case of "Show full table", lex->verbose
 is true to indicate table type is required. In 5.0, this check was
 present which got missing in >=5.5.

Fix:
 Added the required check to avoid opening FRM files unnecessarily in case
 of "Show tables".

sql/sql_show.cc

@@ -3198,39 +3198,44 @@ fill_schema_table_by_open(THD *thd, bool is_show_fields_or_keys,
 
 static int fill_schema_table_names(THD *thd, TABLE *table,
                                    LEX_STRING *db_name, LEX_STRING *table_name,
-                                   bool with_i_schema)
+                                   bool with_i_schema,
+                                   bool need_table_type)
 {
-  if (with_i_schema)
+  /* Avoid opening FRM files if table type is not needed. */
+  if (need_table_type)
   {
-    table->field[3]->store(STRING_WITH_LEN("SYSTEM VIEW"),
-                           system_charset_info);
-  }
-  else
-  {
-    enum legacy_db_type not_used;
-    char path[FN_REFLEN + 1];
-    (void) build_table_filename(path, sizeof(path) - 1, db_name->str, 
-                                table_name->str, reg_ext, 0);
-    switch (mysql_frm_type(thd, path, &not_used)) {
-    case FRMTYPE_ERROR:
-      table->field[3]->store(STRING_WITH_LEN("ERROR"),
-                             system_charset_info);
-      break;
-    case FRMTYPE_TABLE:
-      table->field[3]->store(STRING_WITH_LEN("BASE TABLE"),
-                             system_charset_info);
-      break;
-    case FRMTYPE_VIEW:
-      table->field[3]->store(STRING_WITH_LEN("VIEW"),
+    if (with_i_schema)
+    {
+      table->field[3]->store(STRING_WITH_LEN("SYSTEM VIEW"),
                              system_charset_info);
-      break;
-    default:
-      DBUG_ASSERT(0);
     }
-    if (thd->is_error() && thd->main_da.sql_errno() == ER_NO_SUCH_TABLE)
+    else
     {
-      thd->clear_error();
-      return 0;
+      enum legacy_db_type not_used;
+      char path[FN_REFLEN + 1];
+      (void) build_table_filename(path, sizeof(path) - 1, db_name->str, 
+                                  table_name->str, reg_ext, 0);
+      switch (mysql_frm_type(thd, path, &not_used)) {
+      case FRMTYPE_ERROR:
+        table->field[3]->store(STRING_WITH_LEN("ERROR"),
+                               system_charset_info);
+        break;
+      case FRMTYPE_TABLE:
+        table->field[3]->store(STRING_WITH_LEN("BASE TABLE"),
+                               system_charset_info);
+        break;
+      case FRMTYPE_VIEW:
+        table->field[3]->store(STRING_WITH_LEN("VIEW"),
+                               system_charset_info);
+        break;
+      default:
+        DBUG_ASSERT(0);
+      }
+      if (thd->is_error() && thd->main_da.sql_errno() == ER_NO_SUCH_TABLE)
+      {
+        thd->clear_error();
+        return 0;
+      }
     }
   }
   if (schema_table_store_record(thd, table))
@@ -3551,7 +3556,8 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
           if (schema_table_idx == SCH_TABLE_NAMES)
           {
             if (fill_schema_table_names(thd, tables->table, db_name,
-                                        table_name, with_i_schema))
+                                        table_name, with_i_schema,
+                                        lex->verbose))
               continue;
           }
           else