Is It key_buffer or key_buffer_size?

I search the internet regarding the correct variable in my.cnf file. Some said that key_buffer_size is deprecated, but some said that key_buffer_size is the correct variable in my.cnf.

So, what is really the correct variable here? Is it key_buffer or key_buffer_size?

I'm using Ubuntu 12.04.

And also I have the two key_buffer variable in my.cnf file. This is what I got after installing MySQL.

The first one is located under this:

[mysqld]
key_buffer              = 16M

The other one is located under this:

[isamchk]
key_buffer              = 16M

Solution 1:

I don't think key_buffer_size is deprecated, mysql use key_buffer_size in the documentation on their website from the earliest available right up to the latest version. There is also a bug report that requests deprecated variables emit warnings at startup which suggests that it's key_buffer that is deprecated.

I personally would go with the documentation as it should be authoritative and whilst the internet is full of useful information it's also full of misinformation.

Having said that it seems like mysql goes out of it's way to match variable names you provide to it's variables and will do so as long as the name you provide is unique

With key_buffer_size = 16m

mysql> show variables like '%key_buffer%';
+-----------------+----------+
| Variable_name   | Value    |
+-----------------+----------+
| key_buffer_size | 16777216 |
+-----------------+----------+
1 row in set (0.00 sec)

Change to key_buffer = 6m

mysql> show variables like '%key_buffer%';
+-----------------+---------+
| Variable_name   | Value   |
+-----------------+---------+
| key_buffer_size | 6291456 |
+-----------------+---------+
1 row in set (0.00 sec)

Change to key_b =16m

mysql> show variables like '%key_buffer%';
+-----------------+----------+
| Variable_name   | Value    |
+-----------------+----------+
| key_buffer_size | 16777216 |
+-----------------+----------+
1 row in set (0.00 sec)

Change to key_ = 16m and mysql fails to start as key_ isn't unique.