前言
对于MySQL的理解，我认为很多性能优化工作、主从主主复制都是在调整参数，来适应不同时期不同数量级的数据。
故，理解透彻my.cnf里的参数是永恒的话题；只有理解透彻了参数设置，才能在某些方面对数据库进行调优。
前几天刚接手一个MySQL数据，操作系统为Ubuntu 16.04.5 LTS， 数据库版本为5.7.23-0ubuntu0.16.04.1（APT方式安装的MySQL）。这个操作系统下的MySQL的配置文件my.cnf很多地方都让人有点不适应（跟之前的MySQL环境有些出入，之前都是维护RHEL、CentOS等操作系统环境下的MySQL）。
遂研究总结了一下。具体如下所示：
root@mylnx12:~# find / -name "my.cnf"/etc/alternatives/my.cnf/etc/mysql/my.cnf/var/lib/dpkg/alternatives/my.cnfroot@mylnx12:~# locate my.cnf/etc/alternatives/my.cnf/etc/mysql/my.cnf/etc/mysql/my.cnf.fallback/var/lib/dpkg/alternatives/my.cnfroot@mylnx12:~# mysql --help | grep my.cnf order of preference, my.cnf, $MYSQL_TCP_PORT,/etc/my.cnf /etc/mysql/my.cnf ~/.my.cnf root@mylnx12:~# mysqld --verbose --help | grep -A 1 'Default options'Default options are read from the following files in the given order:/etc/my.cnf /etc/mysql/my.cnf ~/.my.cnf
从上面这些信息判断，MySQL的参数文件为/etc/mysql/my.cnf， 但是其他几个my.cnf又是什么情况呢？
root@mylnx12:~# ls -lrt /etc/alternatives/my.cnflrwxrwxrwx 1 root root 20 Sep 28 16:28 /etc/alternatives/my.cnf -> /etc/mysql/mysql.cnf
从上面信息可以看出，/etc/alternatives/my.cnf 其实是一个软连接，指向参数文件/etc/mysql/mysql.cnf
root@mylnx12:~# cat /var/lib/dpkg/alternatives/my.cnfauto/etc/mysql/my.cnf /etc/mysql/my.cnf.fallback100/etc/mysql/mysql.cnf200
光从上面这些信息，我们还看不出/var/lib/dpkg/alternatives/my.cnf与其它配置文件my.cnf是什么关系。那么我们先来看看参数文件/etc/mysql/my.cnf,从下面信息，可以看出“/etc/mysql/my.cnf”是全局配置，“~/.my.cnf”隐藏文件是个人用户设置.
root@mylnx12:~# cat /etc/mysql/my.cnf## The MySQL database server configuration file.## You can copy this to one of:# - "/etc/mysql/my.cnf" to set global options,# - "~/.my.cnf" to set user-specific options.# # One can use all long options that the program supports.# Run program with --help to get a list of available options and with# --print-defaults to see which it would actually understand and use.## For explanations see# http://dev.mysql.com/doc/mysql/en/server-system-variables.html ## * IMPORTANT: Additional settings that can override those from this file!# The files must end with '.cnf', otherwise they'll be ignored.# !includedir /etc/mysql/conf.d/!includedir /etc/mysql/mysql.conf.d/
但是/etc/mysql/my.cnf参数文件下面没有任何参数设置，只看到下面两行设置，表示导入这两个目录里面的配置文件。
!includedir /etc/mysql/conf.d/
#表示包含/etc/mysql/conf.d/这个路径下面的配置文件，前提是必须以为.cnf为后缀
!includedir /etc/mysql/mysql.conf.d/
#表示包含/etc/mysql/mysql.conf.d/这个路径下面的配置文件，前提是必须以为.cnf为后缀
其实MySQL的相关配置都位于mysqld.cnf（/etc/mysql/mysql.conf.d/mysqld.cnf）下面。使用相关参数测试了一下，确实都能生效。这种设置确实有点让刚接触的人有点不适应。暂时先总结到此！
root@mylnx12:~# cd /etc/mysql/mysql.conf.d/root@mylnx12:/etc/mysql/mysql.conf.d# ls -lrttotal 8-rw-r--r-- 1 root root 21 Feb 4 2017 mysqld_safe_syslog.cnf-rw-r--r-- 1 root root 3148 Oct 6 23:34 mysqld.cnfroot@mylnx12:/etc/mysql/mysql.conf.d# cat mysqld.cnf## The MySQL database server configuration file.## You can copy this to one of:# - "/etc/mysql/my.cnf" to set global options,# - "~/.my.cnf" to set user-specific options.# # One can use all long options that the program supports.# Run program with --help to get a list of available options and with# --print-defaults to see which it would actually understand and use.## For explanations see# http://dev.mysql.com/doc/mysql/en/server-system-variables.html # This will be passed to all mysql clients# It has been reported that passwords should be enclosed with ticks/quotes# escpecially if they contain "#" chars...# Remember to edit /etc/mysql/debian.cnf when changing the socket location. # Here is entries for some specific programs# The following values assume you have at least 32M ram [mysqld_safe]socket = /var/run/mysqld/mysqld.socknice = 0 [mysqld]## * Basic Settings#user = mysqlpid-file = /var/run/mysqld/mysqld.pidsocket = /var/run/mysqld/mysqld.sockport = 3306basedir = /usrdatadir = /var/lib/mysqltmpdir = /tmplc-messages-dir = /usr/share/mysqlskip-external-lockinglog_bin = mylnx12_binserver_id = 0character-set-server=utf8mb4collation-server=utf8mb4_general_ci ## Instead of skip-networking the default is now to listen only on# localhost which is more compatible and is not less secure.bind-address = 10.21.6.7## * Fine Tuning#key_buffer_size = 16Mmax_allowed_packet = 100Mthread_stack = 192Kthread_cache_size = 8# This replaces the startup script and checks MyISAM tables if needed# the first time they are touchedmyisam-recover-options = BACKUP#max_connections = 100#table_cache = 64#thread_concurrency = 10## * Query Cache Configuration#query_cache_limit = 1Mquery_cache_size = 16M## * Logging and Replication## Both location gets rotated by the cronjob.# Be aware that this log type is a performance killer.# As of 5.1 you can enable the log at runtime!#general_log_file = /var/log/mysql/mysql.log#general_log = 1## Error log - should be very few entries.#log_error = /var/log/mysql/error.log## Here you can see queries with especially long duration#log_slow_queries = /var/log/mysql/mysql-slow.log#long_query_time = 2#log-queries-not-using-indexes## The following can be used as easy to replay backup logs or for replication.# note: if you are setting up a replication slave, see README.Debian about# other settings you may need to change.#server-id = 1#log_bin = /var/log/mysql/mysql-bin.logexpire_logs_days = 10max_binlog_size = 100M#binlog_do_db = include_database_name#binlog_ignore_db = include_database_name## * InnoDB## InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/.# Read the manual for more InnoDB related options. There are many!## * Security Features## Read the manual, too, if you want chroot!# chroot = /var/lib/mysql/## For generating SSL certificates I recommend the OpenSSL GUI "tinyca".## ssl-ca=/etc/mysql/cacert.pem# ssl-cert=/etc/mysql/server-cert.pem#: ssl-key=/etc/mysql/server-key.pem
总结
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