Bug #16869534 QUERYING SUBSET OF COLUMNS DOESN'T USE TABLE CACHE; OPENED_TABLES I

Description: When querying a subset of columns from the information_schema.TABLES

Analysis: When information about tables is collected for statements like
"SELECT ENGINE FROM I_S.TABLES" we do not perform full-blown table opens
in SE, instead we only use information from table shares from the Table
Definition Cache or .FRMs. Still in order to simplify I_S implementation
mock TABLE objects are created from TABLE_SHARE during this process.
This is done by calling open_table_from_share() function with special
arguments. Since this function always increments "Opened_tables" counter,
calls to it can be mistakingly interpreted as full-blown table opens in SE.

Note that claim that "'SELECT ENGINE FROM I_S.TABLES' statement doesn't
use Table Cache" is nevertheless factually correct. But it misses the
point, since such statements a) don't use full-blown TABLE objects and
therefore don't do table opens b) still use Table Definition Cache.

Fix: We are now incrementing the counter when db_stat(i.e open flags for ha_open(

we have considered an optimization which would use TABLE objects from
Table Cache when available instead of constructing mock TABLE objects,
but found it too intrusive for stable releases.

mysql-test/r/create.result

@@ -291,7 +291,7 @@ Level	Code	Message
 Note	1050	Table 't1' already exists
 show status like "Opened_tables";
 Variable_name	Value
-Opened_tables	2
+Opened_tables	1
 select * from t1;
 a	b
 1	1

mysql-test/r/information_schema.result

@@ -1965,5 +1965,20 @@ event_object_table	trigger_name
 # Clean-up.
 drop database mysqltest;
 #
+# Test for bug #16869534 - "QUERYING SUBSET OF COLUMNS DOESN'T USE TABLE
+#                           CACHE; OPENED_TABLES INCREASES"
+#
+SELECT * FROM INFORMATION_SCHEMA.TABLES;
+SELECT VARIABLE_VALUE INTO @val1 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE
+VARIABLE_NAME LIKE 'Opened_tables';
+SELECT ENGINE FROM INFORMATION_SCHEMA.TABLES;
+# The below SELECT query should give same output as above SELECT query.
+SELECT VARIABLE_VALUE INTO @val2 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE
+VARIABLE_NAME LIKE 'Opened_tables';
+# The below select should return '1'
+SELECT @val1 = @val2;
+@val1 = @val2
+1
+#
 # End of 5.5 tests
 #

mysql-test/t/information_schema.test

@@ -1782,6 +1782,23 @@ disconnect con12828477_3;
 --echo # Clean-up.
 drop database mysqltest;
 
+--echo #
+--echo # Test for bug #16869534 - "QUERYING SUBSET OF COLUMNS DOESN'T USE TABLE
+--echo #                           CACHE; OPENED_TABLES INCREASES"
+--echo #
+--disable_result_log
+SELECT * FROM INFORMATION_SCHEMA.TABLES;
+--enable_result_log
+SELECT VARIABLE_VALUE INTO @val1 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE
+  VARIABLE_NAME LIKE 'Opened_tables';
+--disable_result_log
+SELECT ENGINE FROM INFORMATION_SCHEMA.TABLES;
+--enable_result_log
+--echo # The below SELECT query should give same output as above SELECT query.
+SELECT VARIABLE_VALUE INTO @val2 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE
+  VARIABLE_NAME LIKE 'Opened_tables';
+--echo # The below select should return '1'
+SELECT @val1 = @val2;
 
 --echo #
 --echo # End of 5.5 tests

sql/table.cc

 /*
-   Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
+   Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -2138,7 +2138,9 @@ int open_table_from_share(THD *thd, TABLE_SHARE *share, const char *alias,
   outparam->no_replicate= outparam->file &&
                           test(outparam->file->ha_table_flags() &
                                HA_HAS_OWN_BINLOGGING);
-  thd->status_var.opened_tables++;
+  /* Increment the opened_tables counter, only when open flags set. */
+  if (db_stat)
+    thd->status_var.opened_tables++;
 
   DBUG_RETURN (0);