This article contains descriptions of some known issues and recipes that might help to get the best application performance.
How To Avoid Performance Issues When MySQL Data is Stored on HDD
It is recommended to use SSD to store the data in the MySQL 8.X database. However, if you do need to use the HDD, follow the steps described in the optimizing InnoDB Disk I/O article to avoid performance issues and set the following configuration parameters in the /etc/my.cnf file:
[mysqld] innodb_file_per_table = 0 wait_timeout = 28800
How To Avoid Performance Issues with MySQL optimizer
To minimize the risk of long compilations of SQL queries (which sometimes may take hours or even days; for details, see MySQL documentation), set optimizer_search_depth to 0:
[mysqld] optimizer_search_depth = 0
Usage of The utf8mb4 Character Set (The Full 4-Byte UTF-8 Unicode Encoding) in MySQL
To store supplementary characters (such as 4-byte emojis), configure the options file to use the utf8mb4 character set. Put the following configuration settings in your options file /etc/my.cnf:
[client] default-character-set = utf8mb4 [mysql] default-character-set = utf8mb4 [mysqld] character-set-server = utf8mb4 collation-server = utf8mb4_unicode_ci
MySQL also can load default options from another file (not /etc/my.cnf). In such cases, you have to put the configuration settings in this file. To find out which configuration files your MySQL server uses, run the following command:
$ mysqld --help --verbose 2> /dev/null | grep -A1 'Default options'
You will get the output with MySQL config files names similar to this:
Default options are read from the following files in the given order: /etc/my.cnf /etc/mysql/my.cnf /usr/local/etc/my.cnf ~/.my.cnf
You also can set up the character set and the collation on the other levels as well.
You can also change the defaults for Doctrine so that the generated SQL uses the correct character set. To achieve this, put the following configuration into the config/config.yml file:
doctrine: dbal: charset: utf8mb4 default_table_options: charset: utf8mb4 collate: utf8mb4_unicode_ci
If you use the version of MySQL that is older than 5.7, also add the row_format: DYNAMIC option to the default_table_options section.
For more details, please see the Setting up the Database to be UTF8 article.
Block Nested Loop (BNL) in MySQL 5.6 and later
MySQL 5.6 has a lot of improvements in the query optimizer, but unfortunately, some queries work significantly
slower than in MySQL 5.5. In case of large amounts of data in the database, it is possible to encounter performance issues
related to the new query optimizer. One of the possible solutions might be disabling
This can be achieved in two ways:
If a modification of MySQL configuration file is granted, add the following under the
Another way is to add the following configuration to the
config/config.ymlfiledoctrine: dbal: connections: default: options: # PDO::MYSQL_ATTR_INIT_COMMAND 1002: 'SET @@SESSION.optimizer_switch="block_nested_loop=off";'