MySQL Bugs: #42305: It is not possible to list existing key caches

Bug #42305	It is not possible to list existing key caches
Submitted:	23 Jan 2009 14:53	Modified:	23 Jan 2009 15:20
Reporter:	Sergey Petrunya	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Options	Severity:	S3 (Non-critical)
Version:	5.1/6.0	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
It is possible to have multiple MyISAM Key Caches as described here: 

http://dev.mysql.com/doc/refman/5.0/en/multiple-key-caches.html

One can create a key cache, and then, provided they know key cache name, use it or delete it.  If you forget the name though, you're out -  it is not possible to list what key caches are present.

How to repeat:
One could expect key cache variables to be listable with SHOW VARIABLES but they are not there:

mysql> set global my_new_key_cache.key_buffer_size=5000000;
Query OK, 0 rows affected (2.40 sec)

mysql> select @@my_new_key_cache.key_buffer_size;
+------------------------------------+
| @@my_new_key_cache.key_buffer_size |
+------------------------------------+
|                            4997120 | 
+------------------------------------+
1 row in set (0.00 sec)

# the following will only show the default key cache
mysql> show variables like '%key_buffer_size%';
+-----------------+--------+
| Variable_name   | Value  |
+-----------------+--------+
| key_buffer_size | 999424 | 
+-----------------+--------+
1 row in set (0.00 sec)

Suggested fix:
According to Serg, this is a known limitation (=not a bug) for 5.0, but is a bug for 5.1/6.0 (can't remember which version)  because that version has a mechanism to dynamically inject variables into SHOW VARIABLES list, which could be used to make non-default key caches show up there.

Thank you for the bug report. Verified as described.

Guessing that this bug belongs to Geogi Kodinov

"mysqladmin -uroot debug" can list each keycache.  See also bug #20679