[#MDEV-21468] Implement status variable to track open temporary tables

The Open_tables status variable does not take temporary tables into account. For example:

MariaDB [(none)]> SHOW GLOBAL STATUS LIKE 'Open_tables';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| Open_tables   | 14    |

+---------------+-------+

1 row in set (0.001 sec)

MariaDB [(none)]> CREATE TEMPORARY TABLE db1.tmp_tab (id int);

Query OK, 0 rows affected (0.002 sec)

MariaDB [(none)]> SHOW GLOBAL STATUS LIKE 'Open_tables';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| Open_tables   | 14    |

+---------------+-------+

1 row in set (0.001 sec)

MariaDB [(none)]> INSERT INTO db1.tmp_tab VALUES (1);

Query OK, 1 row affected (0.000 sec)

MariaDB [(none)]> SHOW GLOBAL STATUS LIKE 'Open_tables';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| Open_tables   | 14    |

+---------------+-------+

1 row in set (0.001 sec)

I think that we should have a status variable that tracks the number of open temporary tables--both globally and for a given session. Maybe it could be called Open_temporary_tables.

Would it also make sense to create Opened_temporary_tables to keep track of all previously opened temporary tables, similar to Opened_tables? Or does Com_create_temporary_table effectively serve the same purpose?

[MDEV-21468] Implement status variable to track open temporary tables Created: 2020-01-13 Updated: 2020-01-30
Status:	Open
Project:	MariaDB Server
Component/s:	Data Definition - Temporary, Variables
Fix Version/s:	None

[MDEV-21468] Implement status variable to track open temporary tables Created: 2020-01-13 Updated: 2020-01-30