=== Installation ===
To get started, [https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Managing_Confined_Services/chap-Managing_Confined_Services-MySQL.html installing MySQL on RHEL] is as simple as <source lang="bash">yum install mysql-server</source>. However, you might get a message that your system is not registered to Red Hat Subscription Management (RHN in the old days), and thus the packages are not visible. To remedy this, you would of course use <code>subscription-manager</code> to register the host with Red Hat Subscription Management.
password=giveMeSomeDBgoodne55
</source>
==Create a DB and user==
<source lang="sql">
CREATE DATABASE mediawiki;
GRANT ALL PRIVILEGES ON mediawiki.* TO 'example_user'@'localhost' IDENTIFIED BY 'secretpass';
</source>
==Set Password for Root user==
The following command issues a new password for the root user while at the same time dictating which authentication plugin <ref>https://mariadb.com/kb/en/library/authentication-plugin-pam/</ref> to use.
<source lang="sql">
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'secretpass';
</source>
Note: Since the introduction of [https://mariadb.com/kb/en/library/development-pluggable-authentication/ Pluggable Authentication] in MySQL 5.7 and also MariaDB since 5.2, there is a "[https://mariadb.com/kb/en/library/authentication-plugin-unix-socket/ unix_socket]" plugin which authenticates the current user by their login to the OS, and thus NOT a password. If you have trouble setting the password, it's probably because you need to also specify the '''mysql_native_password''' auth at the same time <ref>https://www.percona.com/blog/2016/03/16/change-user-password-in-mysql-5-7-with-plugin-auth_socket/</ref>
==What's going on?==
Want to find out what's going on in your MySQL server, but don't want to install client tools and access? Just make sure that the General Query Log is turned on, and tail the log file:
<source lang="sql">
SHOW VARIABLES LIKE "general_log%";
+------------------+----------------------------+
| Variable_name | Value |
+------------------+----------------------------+
| general_log | OFF |
| general_log_file | /var/run/mysqld/mysqld.log |
+------------------+----------------------------+
mysql> SET GLOBAL general_log = 'ON';
</source>
Then you can tail the log file to see what it's doing:<source lang="bash">tail -f /var/run/mysqld/mysqld.log</source>
'''Be sure to turn off the log''' or your disk will fill up and you will not be happy.
<source lang="sql">
mysql> SET GLOBAL general_log = 'OFF';
</source>
If you want more info than you can get from the direct query logging, then try [http://mtop.sourceforge.net/|mtop]
==Show grants==
<code>SHOW GRANTS</code> only shows privs for the current user.
<source lang="sql">
show grants;
show grants for 'root'@'localhost';
</source>
But this bash one-liner will show you all grants. <code>-B --batch</code> disables interactive behavior and doesn't use the history file
<code>-N --skip-column-names</code> <code>-e --execute</code> executes a command and quits (disables --force and history file.)
<source lang="bash">
mysql -B -N -e "SELECT DISTINCT CONCAT('SHOW GRANTS FOR ''',user,'''@''',host,''';') AS query FROM user" mysql | mysql
</source>
==Fixing CHARSET and COLLATION==
See the article about [[Collation]]
==Working at the Console==
Reading output from the mysql command line client is notoriously ugly/hard. With the <code>-s --silent</code> or <code>-B --batch</code> options, you can get output that is more readable.
==Experts==
Rick James https://mysql.rjweb.org/
Major Hayden https://major.io/tags/database/ https://github.com/major
==Tools==
Aside from [[mysqldump]], there are also mysqlcheck, mysql_upgrade and other [https://dev.mysql.com/doc/refman/5.7/en/programs-client.html client programs].
#[https://www.mysql.com/products/workbench/ MySQL Workbench] is a great visual tool, but behind several obstacles and Oracles.
#[https://dbeaver.io/ DBeaver]
#[https://github.com/major/MySQLTuner-perl/blob/master/INTERNALS.md MySQLTuner] by the aforementioned Major Hayden (he made a Python version too)
#[https://www.percona.com/software/database-tools/percona-toolkit Percona Toolkit] <code>wget <nowiki>https://downloads.percona.com/downloads/percona-toolkit/3.5.7/binary/redhat/8/x86_64/percona-toolkit-3.5.7-1.el8.x86_64.rpm</nowiki></code> <code>dnf install percona-toolkit-3.5.7-1.el8.x86_64.rpm</code> <code>pt-mysql-summary</code>
#http://mysqlsandbox.net/index.html MySQL sandbox could be useful for playing around with multiple databases in development.
==Logs==
Your data directory can fill up with binary logs unless you rotate them.
Information below comes from https://dba.stackexchange.com/questions/41050/is-it-safe-to-delete-mysql-bin-files
'''Don't''' just delete the files. Use MySQL to do it.
Either pass the name of a particular file, or a timestamp and MySQL will clear out the binary logs up to the one just specified (or the date)
;Example :
<source lang="mysql">
-- consolidate the logs up to midnight 3 days ago
PURGE BINARY LOGS BEFORE DATE(NOW() - INTERVAL 3 DAY) + INTERVAL 0 SECOND;
-- consolidate the logs up to the file specified
PURGE BINARY LOGS TO `mysql-bin.000223`;
</source>
;Which File to choose?:
If you want to know which log files are in use so that you can remove superfluous ones without interrupting replication, go to your slave database and issue <tt>SHOW SLAVE STATUS\G
</tt>
You'll see entries for
*Master_Log_File
*Relay_Master_Log_File
When replication has little or no lag these are usually the same value. If there is a lot of replication lag, they will be different values. Choose the value for <tt>Relay_Master_Log_File</tt> just to be safe. Go back to the DB master and issue <tt>PURGE BINARY LOGS TO mysql-bin.000337</tt> where mysql-bin.000337 is the value of <tt>Relay_Master_Log_File</tt>
;Persistence :
To persist this setup so your data directory doesn't fill up again, issue
<source lang="mysql">
SET GLOBAL expire_logs_days = 3;
</source>
To put the setting into effect immediately. And for the next time MySQL is restarted, add to <tt>/etc/my.cnf</tt>
<source lang="ini">
[mysqld]
expire_logs_days=3
</source>
Since the binlongs are used to recover the database state after a crash, this assumes that you are making database backups every day. If you only backup once per week, you would want at least 7 days worth of binlogs.
==Tuning Reference==
#https://mariadb.com/kb/en/library/configuring-mariadb-for-optimal-performance
#https://www.experts-exchange.com/questions/29060302/Tune-MySQL-to-32GB-RAM.html
#https://www.tecmint.com/mysql-mariadb-performance-tuning-and-optimization/
#https://www.percona.com/blog/10-mysql-performance-tuning-settings-after-installation/
#https://www.percona.com/blog/2016/10/12/mysql-5-7-performance-tuning-immediately-after-installation/
#https://www.percona.com/blog/2009/11/16/table_cache-negative-scalability/
==MediaWiki==
As of 2024-04-23 MediaWiki only requires MariaDB 10.3.x or MySQL 5.7.x for installation<ref>https://www.mediawiki.org/wiki/Manual:Installation_requirements#Database_server</ref> However, these are out of support. MariaDB is available in versions ranging from [https://mariadb.com/kb/en/changes-and-improvements-in-mariadb-10-4/ 10.4] - 10.11 and 11.0 - 11.5 The latest release in the 10.4 series is 10.4.33, released on 2024-02-07
Practically, this means that even if the database doesn't show errors, it could become vulnerable to attack or corruption at any time. And, tools like MySQLTuner, VSCode, PHPMyAdmin, etc. may not support the old version any longer.
Starting in REL1_35, MediaWiki uses the [https://www.doctrine-project.org/projects/dbal.html Doctrine Database Abstraction Layer] (DBAL)
<br />
==Footnotes==
<references />
[[Category:Database]]