Description:
Structured system variables are not displayed with SHOW VARIABLES nor have a status in SHOW STATUS.
This makes it sometimes difficult to see what happens and during Consulting Gig you are not aware of the use of this extra data structures if customer not explictly mentioned it.
How to repeat:
SET GLOBAL hot.key_buffer_size=32*1024*1024;
SELECT @@global.cold.key_buffer_size;
+-------------------------------+
| @@global.cold.key_buffer_size |
+-------------------------------+
| 33554432 |
+-------------------------------+
SHOW GLOBAL VARIABLES LIKE '%key%size';
+----------------------+----------+
| Variable_name | Value |
+----------------------+----------+
| key_buffer_size | 33554432 |
| key_cache_block_size | 1024 |
+----------------------+----------+
SHOW GLOBAL STATUS LIKE '%key_blocks%used';
+-------------------+-------+
| Variable_name | Value |
+-------------------+-------+
| Key_blocks_unused | 0 |
| Key_blocks_used | 28995 |
+-------------------+-------+
Suggested fix:
Add all structured system variables to the general output (show status, show variables, mysqladmin --extended) etc.