Mycat資料庫中介軟體的安裝與使用
MyCAT是mysql中介軟體，前身是阿里大名鼎鼎的Cobar，Cobar在開源了一段時間後，不了了之。於是MyCAT扛起了這面大旗，在大資料時代，其重要性愈發彰顯。這篇文章主要是MyCAT的入門部署。
一、安裝java
因Mycat是用java開發的，所以需要在實驗環境下安裝java，官方建議jdk1.7及以上版本
Java Oracle官方下載地址為：
解壓jdk-7u79-linux-x64.tar.gz檔案，並配置java的環境變數
# tar xvf jdk-7u79-linux-x64.tar.gz
# mv jdk1.7.0_79/ /usr/local/
編輯/etc/profile檔案
# vim /etc/profile 新增如下內容
JAVA_HOME=/usr/local/jdk1.7.0_79
JAVA_BIN=/usr/local/jdk1.7.0_79/bin
PATH=$JAVA_BIN:$PATH
CLASSPATH=$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export JAVA_HOME JAVA_BIN PATH CLASSPATH
# source /etc/profile --使/etc/profile檔案生效
# java -version
java version "1.7.0_79" Java(TM) SE Runtime Environment (build1.7.0_79-b15) Java HotSpot(TM) 64-Bit Server VM (build 24.79-b02, mixed mode)
二、安裝MySQL
MySQL官方下載地址如下：
裡面有各種版本，包括RPM，二進位制，原始碼包。
為了方便起見，我這裡選擇是RPM包
# yum install -y mysql-community-server-5.6.26-2.el5.x86_64.rpm
啟動MySQL
# /etc/init.d/mysqld start
Starting mysqld (via systemctl): [ OK ]
為root賬戶建立密碼
# mysqladmin -u root password "123456"
建議為123456，後面MyCAT配置檔案schema.xml中會用到
三、安裝MyCAT
建立MyCAT使用者並設定密碼
# useradd mycat
# passwd mycat
解壓MyCAT檔案
# tar xvf Mycat-server-1.5-alpha-20151221110028-linux.tar.gz
# mv mycat/ /usr/local/
設定mycat目錄的屬主和屬組
# chown -R mycat.mycat /usr/local/mycat/
四、測試MyCAT
首先在MySQL上建立三個資料庫：db1，db2，db3。
mysql> create database db1; Query OK, 1 row affected (0.00 sec) mysql> create database db2; Query OK, 1 row affected (0.00 sec) mysql> create database db3; Query OK, 1 row affected (0.00 sec)
啟動mycat服務
# cd /usr/local/mycat/bin/
# ./mycat start
Starting Mycat-server...
檢視mycat服務是否啟動
# ps -ef |grep mycat
root 9640 7257 0 22:47 pts/3 00:00:00 grep --color=auto mycat
並沒有啟動
檢視日誌
# cd /usr/local/mycat/logs/
# cat wrapper.log
STATUS | wrapper | 2016/01/07 22:44:23 | --> Wrapper Started as Daemon STATUS | wrapper | 2016/01/07 22:44:23 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:25 | JVM exited while loading the application. INFO | jvm 1 | 2016/01/07 22:44:25 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:29 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:29 | JVM exited while loading the application. INFO | jvm 2 | 2016/01/07 22:44:29 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:34 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:34 | JVM exited while loading the application. INFO | jvm 3 | 2016/01/07 22:44:34 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:38 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:38 | JVM exited while loading the application. INFO | jvm 4 | 2016/01/07 22:44:38 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known STATUS | wrapper | 2016/01/07 22:44:42 | Launching a JVM... ERROR | wrapper | 2016/01/07 22:44:43 | JVM exited while loading the application. INFO | jvm 5 | 2016/01/07 22:44:43 | Error: Exception thrown by the agent : java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: MySQL-Server1: MySQL-Server1: Name or service not known FATAL | wrapper | 2016/01/07 22:44:43 | There were 5 failed launches in a row, each lasting less than 300 seconds. Giving up. FATAL | wrapper | 2016/01/07 22:44:43 | There may be a configuration problem: please check the logs. STATUS | wrapper | 2016/01/07 22:44:43 | <-- Wrapper Stopped
根據報錯資訊，懷疑主機名沒有繫結
修改hosts檔案，繫結主機名
# vim /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 192.168.244.144 MySQL-Server1
重新啟動mycat服務
# cd /usr/local/mycat/bin/
# ./mycat start
這次mycat正常啟動
# ps -ef |grep mycat
root 10725 1 0 22:54 ? 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/mycat root 10881 7257 0 22:55 pts/3 00:00:00 grep --color=auto mycat
下面以Travelrecord為例，來進行插入，查詢，路由分析等基本操作。
首先利用mycat連線mysql資料庫
# mysql -utest -ptest -h127.0.0.1 -P8066 -DTESTDB
其中8066是mycat的監聽埠，類似於mysql的3306埠，其中-u，-p，-h分別是使用者名稱，密碼和主機，-D是連線的邏輯庫。
至於為什麼是這些，這個跟配置檔案有關。
紅色部分表明連線的是mycat。
建立Travelrecord表
create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int);
插入資料
mysql> insert into travelrecord(id,user_id,traveldate,fee,days) values(1,'Victor',20160101,100,10); Query OK, 1 row affected (0.00 sec) mysql> insert into travelrecord(id,user_id,traveldate,fee,days) values(5000001,'Job',20160102,100,10); Query OK, 1 row affected (0.00 sec) mysql> insert into travelrecord(id,user_id,traveldate,fee,days) values(10000001,'Slow',20160103,100,10); Query OK, 1 row affected (0.00 sec)
至於ID為什麼取三個值，這個與conf目錄下autopartition-long.txt的定義有關，這個檔案主要定義auto-sharding-long的規則。
# range start-end ,data node index # K=1000,M=10000. 0-500M=0 500M-1000M=1 1000M-1500M=2
我主要是測試在id取不同區間的值時，分片的效果。
下面來看看分片的效果
mysql> select * from db1.travelrecord; +----+---------+------------+------+------+ | id | user_id | traveldate | fee | days | +----+---------+------------+------+------+ | 1 | Victor | 2016-01-01 | 100 | 10 | +----+---------+------------+------+------+ 1 row in set (0.00 sec) mysql> select * from db2.travelrecord; +---------+---------+------------+------+------+ | id | user_id | traveldate | fee | days | +---------+---------+------------+------+------+ | 5000001 | Job | 2016-01-02 | 100 | 10 | +---------+---------+------------+------+------+ 1 row in set (0.00 sec) mysql> select * from db3.travelrecord; +----------+---------+------------+------+------+ | id | user_id | traveldate | fee | days | +----------+---------+------------+------+------+ | 10000001 | Slow | 2016-01-03 | 100 | 10 | +----------+---------+------------+------+------+ 1 row in set (0.00 sec)
果然是分配到三個不同的節點上了。
如果想看MyCAT具體會將資料分配到哪個節點上，可通過路由分析。
語法其實蠻簡單，就是SQL語句前加上explain語句。
下面根據explain命令檢視create語句和insert語句具體會分配到哪些Datanode上。
mysql> explain create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int); +-----------+-----------------------------------------------------------------------------------------------------------------------+ | DATA_NODE | SQL | +-----------+-----------------------------------------------------------------------------------------------------------------------+ | dn1 | create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int) | | dn2 | create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int) | | dn3 | create table travelrecord (id bigint not null primary key,user_id varchar(100),traveldate DATE, fee decimal,days int) | +-----------+-----------------------------------------------------------------------------------------------------------------------+ 3 rows in set (0.00 sec) mysql> explain insert into travelrecord(id,user_id,traveldate,fee,days) values(1,'Victor',20160101,100,10); +-----------+----------------------------------------------------------------------------------------------+ | DATA_NODE | SQL | +-----------+----------------------------------------------------------------------------------------------+ | dn1 | insert into travelrecord(id,user_id,traveldate,fee,days) values(1,'Victor',20160101,100,10) | +-----------+----------------------------------------------------------------------------------------------+ 1 row in set (0.01 sec) mysql> explain insert into travelrecord(id,user_id,traveldate,fee,days) values(5000001,'Job',20160102,100,10); +-----------+-------------------------------------------------------------------------------------------------+ | DATA_NODE | SQL | +-----------+-------------------------------------------------------------------------------------------------+ | dn2 | insert into travelrecord(id,user_id,traveldate,fee,days) values(5000001,'Job',20160102,100,10) | +-----------+-------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) mysql> explain insert into travelrecord(id,user_id,traveldate,fee,days) values(10000001,'Slow',20160103,100,10); +-----------+---------------------------------------------------------------------------------------------------+ | DATA_NODE | SQL | +-----------+---------------------------------------------------------------------------------------------------+ | dn3 | insert into travelrecord(id,user_id,traveldate,fee,days) values(10000001,'Slow',20160103,100,10) | +-----------+---------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
總結：
關於MyCAT的配置其實是蠻簡單的，最主要的是熟悉各配置檔案的規則。以上使用者名稱，密碼，如何分庫，都是在配置檔案中定義的，後續，有時間再一一詳表。
關於配置檔案，conf目錄下主要以下三個需要熟悉。
server.xml是Mycat伺服器引數調整和使用者授權的配置檔案
schema.xml是邏輯庫定義和表以及分片定義的配置檔案
rule.xml是分片規則的配置檔案