1.mysqld_multi介绍

mysqld_multi can be used to start, reload, or stop any number of separate mysqld processes running in different TCP/IP ports and UNIX sockets.
mysqld_multi可用于启动，重新加载或停止在不同的TCP / IP端口和UNIX套接字中运行的任意数量的独立mysqld进程。

2.mysqld_multi用法和注意事项

2.1创建专用用户

mysqld服务的MySQL用户对mysqld_multi访问的所有MySQL服务器具有相同的密码。
建议您为由mysqld_multi控制的所有MySQL服务器创建一个通用的“ multi_admin”用户，此用户对mysqld_multi访问的所有MySQL服务器具有相同的密码。该用户需要具有'Shutdown_priv'-特权，出于安全原因，不应具有其他特权。示例：
GRANT SHUTDOWN ON *.* TO multi_admin@localhost IDENTIFIED BY 'password'

2.2PID文件

如果使用mysqld_safe启动mysqld，请确保每个MySQL服务器都有一个单独的pid文件。为了通过mysqld_multi使用mysqld_safe，您需要使用两个选项：

mysqld=/path/to/mysqld_safe
ledir=/path/to/mysqld-binary/

ledir (library executable directory), 是仅mysqld_safe接受的选项，如果尝试将其直接传递给mysqld，则会收到错误消息。因此，最好直接在[mysqld＃]组中使用上述选项。

2.3.DATA DIRECTORY

不建议在同一数据目录中运行许多MySQL服务器。这样做将最终导致不良结果。

Speed penalty
速度惩罚
Risk of table/data corruption
表/数据损坏的风险
Data synchronising problems between the running servers
正在运行的服务器之间的数据同步问题
Heavily media (disk) bound
大量介质（磁盘）绑定
Relies on the system (external) file locking
依靠系统（外部）文件锁定
Is not applicable with all table types. (Such as InnoDB)
不适用于所有表格类型。（例如InnoDB）

2.4.TCP/IP Port

Every server requires one and it must be unique.每个服务器都需要一个，并且必须唯一。

2.5.[mysqld#] Groups

在配置文件中，mysqld group之间有间隔。如实例配置文件中所示，[mysqld1]和[mysqld5]没有配置。

2.6.MySQL Server User

您可以在[mysqld＃]组内传递user = ...选项。在某些情况下，这可能非常方便，但是随后您需要以UNIX root用户身份运行mysqld_multi。

2.7.A Start-up Manage Script for mysqld_multi

在support-files 目录中有一个名为mysqld_multi.server.sh的文件，可以启动和停止多台服务器。您可以将文件放在/etc/init.d/mysqld_multi.server.sh中，并在各种运行级别（根据Linux / Unix标准）建立所需的符号链接。也可以用/etc/init.d/mysql.server脚本替换它。
在使用之前，必须在my.cnf文件，并添加[mysqld_multi]和[mysqld＃]组。
mysqld_multi配置示例：

[mysqld_multi]
mysqld     = /usr/local/mysql/bin/mysqld_safe
mysqladmin = /usr/local/mysql/bin/mysqladmin
user       = multi_admin
password   = my_password

[mysqld2]
socket     = /tmp/mysql.sock2
port       = 3307
pid-file   = /usr/local/mysql/data2/hostname.pid2
datadir    = /usr/local/mysql/data2
language   = /usr/local/mysql/share/mysql/english
user       = unix_user1

[mysqld3]
mysqld     = /path/to/mysqld_safe
ledir      = /path/to/mysqld-binary/
mysqladmin = /path/to/mysqladmin
socket     = /tmp/mysql.sock3
port       = 3308
pid-file   = /usr/local/mysql/data3/hostname.pid3
datadir    = /usr/local/mysql/data3
language   = /usr/local/mysql/share/mysql/swedish
user       = unix_user2

[mysqld4]
socket     = /tmp/mysql.sock4
port       = 3309
pid-file   = /usr/local/mysql/data4/hostname.pid4
datadir    = /usr/local/mysql/data4
language   = /usr/local/mysql/share/mysql/estonia
user       = unix_user3
 
[mysqld6]
socket     = /tmp/mysql.sock6
port       = 3311
pid-file   = /usr/local/mysql/data6/hostname.pid6
datadir    = /usr/local/mysql/data6
language   = /usr/local/mysql/share/mysql/japanese
user       = unix_user4

support-files/mysqld_multi.server

#!/bin/sh
#
# A simple startup script for mysqld_multi by Tim Smith and Jani Tolonen.
# This script assumes that my.cnf file exists either in /etc/my.cnf or
# /root/.my.cnf and has groups [mysqld_multi] and [mysqldN]. See the
# mysqld_multi documentation for detailed instructions.
#
# This script can be used as /etc/init.d/mysql.server
#
# Comments to support chkconfig on RedHat Linux
# chkconfig: 2345 64 36
# description: A very fast and reliable SQL database engine.
#
# Version 1.0
#

basedir=/usr/local/mysql
bindir=/usr/local/mysql/bin

if test -x $bindir/mysqld_multi
then
  mysqld_multi="$bindir/mysqld_multi";
else
  echo "Can't execute $bindir/mysqld_multi from dir $basedir";
  exit;
fi

case "$1" in
    'start' )
        "$mysqld_multi" start $2
        ;;
    'stop' )
        "$mysqld_multi" stop $2
        ;;
    'report' )
        "$mysqld_multi" report $2
        ;;
    'restart' )
        "$mysqld_multi" stop $2
        "$mysqld_multi" start $2
        ;;
    *)
        echo "Usage: $0 {start|stop|report|restart}" >&2
        ;;
esac

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