这篇文章主要介绍“MyCat怎么实现MySQL一主两从读写分离”，在日常操作中，相信很多人在MyCat怎么实现MySQL一主两从读写分离问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”MyCat怎么实现MySQL一主两从读写分离”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
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环境搭建（一主两从）：
macat：192.168.8.30
master：192.168.8.31
slave1：192.168.8.32
slave2：192.168.8.33
工具包：
java-1.8.0-openjdk-1.8.0.161-2.b14.el7.x86_64
Mycat-server-1.6.6.1-release-20181031195535-linux.tar.gz
一、安装JDK和MyCat
系统已安装JDK，查看安装路径
[root@mycat ~]# java -version
openjdk version "1.8.0_161"
OpenJDK Runtime Environment (build 1.8.0_161-b14)
OpenJDK 64-Bit Server VM (build 25.161-b14, mixed mode)
[root@mycat ~]# ls -l /usr/bin/java
lrwxrwxrwx. 1 root root 22 Oct 22 10:30 /usr/bin/java -> /etc/alternatives/java
[root@mycat ~]# ls -l /etc/alternatives/java
lrwxrwxrwx. 1 root root 71 Oct 22 10:30 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.161-2.b14.el7.x86_64/jre/bin/java
安装MyCat
cd /software
tar zxvf Mycat-server-1.6.6.1-release-20181031195535-linux.tar.gz
cp -r mycat /usr/local/
配置环境变量
[root@mycat ~]# cat ~/.bash_profile
# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
# User specific environment and startup programs
export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.161-2.b14.el7.x86_64
export JRE_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.161-2.b14.el7.x86_64/jre
export MYCAT_HOME=/usr/local/mycat
PATH=$PATH:/mysql/app/mysql/bin:/mysql/app/xtrabackup/bin:$HOME/bin:/usr/bin:/sbin:/bin:$MYCAT_HOME/bin:$JAVA_HOME/bin
export PATH
二、创建测试库
master创建，slave同步
create database testdb1;
create table testdb1.t11(name1 varchar(40),name2 varchar(40),name3 varchar(40));
create database testdb2;
create table testdb2.t21(name1 varchar(40),name2 varchar(40),name3 varchar(40));
create database testdb3;
create table testdb3.t31(name1 varchar(40),name2 varchar(40),name3 varchar(40));
三、配置schema.xml
select user()
其中 checkSQLschema 表明是否检查并过滤 SQL 中包含schema的情况，如逻辑库为mycatdb1，则可能写为 select * from mycatdb1.t11，此时会自动过滤 mycatdb1，SQL变为select * from t11，若不会出现上述写法，则可以关闭属性为false。
sqlMaxLimit默认返回的最大记录数限制，MyCat1.4 版本里面，用户的Limit参数会覆盖掉MyCat的sqlMaxLimit默认设置
schema中的每一个dataHost中的host属性值必须唯一，否则会出现主从在所有dataHost中全部切换的现象
其中，balance 指的负载均衡类型，目前的取值有 4 种：
1. balance="0", 不开启读写分离机制，所有读操作都发送到当前可用的 writeHost 上。
2. balance="1"，全部的readHost与 stand by writeHost 参与select语句的负载均衡，简单的说，当双主双从模式(M1>S1，M2->S2，并且 M1 与 M2 互为主备)，正常情况下，M2,S1,S2 都参与select语句的负载均衡。
3. balance="2"，所有读操作都随机的在 writeHost、readhost 上分发。
4. balance="3"，所有读请求随机的分发到 wiriterHost 对应的 readhost 执行，writerHost 不负担读压力
因此，该配置文件中的 balance="1"意味着作为stand by writeHost的hostS1和hostS2将参与select语句的负载均衡，这就实现了主从的读写分离
switchType 指的是切换的模式，目前的取值也有 4 种：
1. switchType='-1' 表示不自动切换
2. switchType='1' 默认值，表示自动切换
3. switchType='2' 基于MySQL主从同步的状态决定是否切换,心跳语句为 show slave status
MyCat1.4 开始支持MySQL主从复制状态绑定的读写分离机制，让读更加安全可靠，配置如下：
MyCat心跳检查语句配置为 show slave status，dataHost上定义两个新属性：switchType="2"与slaveThreshold="100"，此时意味着开启MySQL主从复制状态绑定的读写分离与切换机制，MyCat 心跳机制通过检测show slave status 中的"Seconds_Behind_Master", "Slave_IO_Running", "Slave_SQL_Running"
三个字段来确定当前主从同步的状态以及 Seconds_Behind_Master 主从复制时延，当 Seconds_Behind_Master 大于 slaveThreshold 时，读写分离筛选器会过滤掉此Slave机器，防止读到很久之前的旧数据，而当主节点宕机后，切换逻辑会检查Slave上的Seconds_Behind_Master 是否为 0，为 0 时则表示主从同步，可以安全切换，否则不会切换。
4. switchType='3'基于 MySQL galary cluster/PXC/mgr 的切换机制（适合集群）（1.4.1），心跳语句为 show status like 'wsrep%'。
四、配置server.xml
mysql
mycatdb1,mycatdb2,mycatdb3
user
mycatdb1,mycatdb2,mycatdb3
true
五、修改MyCat日志级别
vi log4j2.xml
修改
为
六、启动mycat
[root@mycat conf]# /usr/local/mycat/bin/mycat start
Starting Mycat-server...
查看日志
STATUS | wrapper | 2018/11/21 11:08:50 | --> Wrapper Started as Daemon
STATUS | wrapper | 2018/11/21 11:08:51 | Launching a JVM...
INFO | jvm 1 | 2018/11/21 11:08:51 | OpenJDK 64-Bit Server VM warning: ignoring option MaxPermSize=64M; support was removed in 8.0
INFO | jvm 1 | 2018/11/21 11:08:54 | Wrapper (Version 3.2.3) http://wrapper.tanukisoftware.org
INFO | jvm 1 | 2018/11/21 11:08:54 | Copyright 1999-2006 Tanuki Software, Inc. All Rights Reserved.
INFO | jvm 1 | 2018/11/21 11:08:54 |
INFO | jvm 1 | 2018/11/21 11:08:58 | MyCAT Server startup successfully. see logs in logs/mycat.log
查看端口
[root@mycat conf]# netstat -an|grep 8066
tcp6 0 0 :::8066
查看mycat进程
[root@mycat conf]# ps -ef|grep mycat
avahi 646 1 0 09:56 ? 00:00:03 avahi-daemon: running [mycat.local]
root 2653 1 0 11:08 ? 00:00:00 /usr/local/mycat/bin/./wrapper-linux-x86-64 /usr/local/mycat/conf/wrapper.conf wrapper.syslog.ident=mycat wrapper.pidfile=/usr/local/mycat/logs/mycat.pid wrapper.daemonize=TRUE wrapper.lockfile=/var/lock/subsys/myca
root 2655 2653 7 11:08 ? 00:00:07 java -DMYCAT_HOME=. -server -XX:MaxPermSize=64M -XX:+AggressiveOpts -XX:MaxDirectMemorySize=2G -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=1984 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Xmx4G -Xms1G -Djava.library.path=lib -classpath lib/wrapper.jar:conf:lib/asm-4.0.jar:lib/commons-collections-3.2.1.jar:lib/commons-lang-2.6.jar:lib/curator-client-2.11.0.jar:lib/curator-framework-2.11.0.jar:lib/curator-recipes-2.11.0.jar:lib/disruptor-3.3.4.jar:lib/dom4j-1.6.1.jar:lib/druid-1.0.26.jar:lib/ehcache-core-2.6.11.jar:lib/fastjson-1.2.12.jar:lib/guava-19.0.jar:lib/hamcrest-core-1.3.jar:lib/hamcrest-library-1.3.jar:lib/jline-0.9.94.jar:lib/joda-time-2.9.3.jar:lib/jsr305-2.0.3.jar:lib/kryo-2.10.jar:lib/leveldb-0.7.jar:lib/leveldb-api-0.7.jar:lib/libwrapper-linux-ppc-64.so:lib/libwrapper-linux-x86-32.so:lib/libwrapper-linux-x86-64.so:lib/log4j-1.2-api-2.5.jar:lib/log4j-1.2.17.jar:lib/log4j-api-2.5.jar:lib/log4j-core-2.5.jar:lib/log4j-slf4j-impl-2.5.jar:lib/mapdb-1.0.7.jar:lib/minlog-1.2.jar:lib/mongo-java-driver-2.11.4.jar:lib/Mycat-server-1.6.6.1-release.jar:lib/mysql-binlog-connector-java-0.16.1.jar:lib/mysql-connector-java-5.1.35.jar:lib/netty-3.7.0.Final.jar:lib/netty-buffer-4.1.9.Final.jar:lib/netty-common-4.1.9.Final.jar:lib/objenesis-1.2.jar:lib/reflectasm-1.03.jar:lib/sequoiadb-driver-1.12.jar:lib/slf4j-api-1.6.1.jar:lib/univocity-parsers-2.2.1.jar:lib/velocity-1.7.jar:lib/wrapper.jar:lib/zookeeper-3.4.6.jar -Dwrapper.key=G87oQ7EZv67RXK9D -Dwrapper.port=32000 -Dwrapper.jvm.port.min=31000 -Dwrapper.jvm.port.max=31999 -Dwrapper.pid=2653 -Dwrapper.version=3.2.3 -Dwrapper.native_library=wrapper -Dwrapper.service=TRUE -Dwrapper.cpu.timeout=10 -Dwrapper.jvmid=1 org.tanukisoftware.wrapper.WrapperSimpleApp io.mycat.MycatStartup start
七、登录mysql，查看逻辑库
[root@mycat ~]# mysql -uroot -pmysql -P8066 -h292.168.8.30
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.29-mycat-1.6.6.1-release-20181031195535 MyCat Server (OpenCloudDB)
Copyright (c) 2009-2018 Percona LLC and/or its affiliates
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show databases;
+----------+
| DATABASE |
+----------+
| mycatdb1 |
| mycatdb2 |
| mycatdb3 |
+----------+
3 rows in set (0.01 sec)
mysql> use mycatdb1;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> show tables;
+-------------------+
| Tables_in_testdb1 |
+-------------------+
| t11 |
+-------------------+
1 row in set (0.04 sec)
mysql> select * from t11;
Empty set (0.22 sec)
八、读写分离验证
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave1 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave1 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave1 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave2 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave1 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave2 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave2 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave2 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave1 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave2 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave1 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave1 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave2 |
+------------+
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select @@hostname"
mysql: [Warning] Using a password on the command line interface can be insecure.
+------------+
| @@hostname |
+------------+
| slave2 |
可以看到读操作全部在slave1和slave2
注意：这里的负载均衡并不是在slave1和slave2上边轮询，而是总体保持负载均衡。
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select * from mycatdb1.t11"
mysql: [Warning] Using a password on the command line interface can be insecure.
+--------+--------+--------+
| name1 | name2 | name3 |
+--------+--------+--------+
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
+--------+--------+--------+
九、主从切换测试
关闭master上的MySQL进程
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1184 (HY000) at line 1: java.net.ConnectException: Connection refused
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1184 (HY000) at line 1: java.net.ConnectException: Connection refused
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "insert into mycatdb1.t11 values(@@hostname,@@hostname,@@hostname)"mysql: [Warning] Using a password on the command line interface can be insecure.
[root@mycat conf]# mysql -uroot -pmysql -P8066 -h292.168.8.30 -e "select * from mycatdb1.t11"
mysql: [Warning] Using a password on the command line interface can be insecure.
+--------+--------+--------+
| name1 | name2 | name3 |
+--------+--------+--------+
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| master | master | master |
| slave1 | slave1 | slave1 |
| slave1 | slave1 | slave1 |
| slave1 | slave1 | slave1 |
+--------+--------+--------+
短暂的连接失败之后，写操作连进slave1，主从切换成功。
到此，关于“MyCat怎么实现MySQL一主两从读写分离”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注创新互联网站，小编会继续努力为大家带来更多实用的文章！
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