Yesterday I decided to upgrade the database server of lefred.be running the latest WordPress to MySQL 8.0.

The previous version was 5.7.19.

My dedicated server is still running on CentOS 6.x, and I had just to enable the MySQL Community 8.0 yum repository and upgrade the rpms:

# yum update mysql-community-server --enablerepo=mysql80-community

After the upgrade, I had to modify my.cnf to remove the lines related to the non regretted Query Cache:

#query_cache_type=0
 …

For the first time since the beginning of my long long career, I decided today to use an advice tool to check my MySQL configuration.

I decided to launch pt-variable-advisor and mysqltuner V2 on one of my MySQL server.
Here are the result outputs :

Then I ask myself what to do with these results, just raw results without much explanations, these tools are supposed to be done for beginners…

Just one example from mysqltuner : Too many temporary tables are being written to disk.  Increase max_heap_table_size and tmp_table_size
If I set the size of my temporary tables at 16Mb, what that’s means, I have to increase to 32Mb, 64Mb or more ?
…

Just how effective is the Query Cache on performance? If you are not comfortable reading the MySQL code you can cheat very easily with the SHOW PROFILE command. This demonstration will show you at a high level the relative impact without and with the Query Cache. First let us confirm the Query Cache is not used.

mysql> SHOW GLOBAL VARIABLES LIKE 'query_cache%';
+------------------------------+---------+
| Variable_name                | Value   |
+------------------------------+---------+
| query_cache_limit            | 1048576 |
| query_cache_min_res_unit     | 4096    |
| query_cache_size             | 0       |
| query_cache_type             | ON      |
| query_cache_wlock_invalidate | OFF     |
+------------------------------+---------+
5 rows in set (0.00 sec)

We now enable profiling.

mysql> SET PROFILING=1;

We run our …