在Mycat教程當中，讀寫與分離也是重要的知識點，大家可要好好學習哦。

測試讀寫分離：

[root@anedbtest01 conf]# cat schema.xml 
<?xml version="1.0"?>
<!DOCTYPE mycat:schema SYSTEM "schema.dtd">
<mycat:schema xmlns:mycat="http://io.mycat/">
    <schema name="testdb" checkSQLschema="true" sqlMaxLimit="100">
        <table name="travelrecord" dataNode="dn1" autoIncrement="true" primaryKey="ID"  /> 
           <table name="t1" dataNode="dn1" autoIncrement="true" primaryKey="ID"  />
       </schema>
    <dataNode name="dn1" dataHost="shard" database="db1" />
    <dataHost name="shard" maxCon="1000" minCon="10" balance="0"  writeType="0" dbType="mysql" dbDriver="native" switchType="1"  slaveThreshold="100">
        <heartbeat>select user()</heartbeat>
        <writeHost host="hostM1" url="127.0.0.1:3306" user="root"  password="123">
            <readHost host="hostS2" url="127.0.0.1:3307" user="root" password="123" />
        </writeHost>
    </dataHost>
</mycat:schema>

balance="0"：讀請求僅發送到writeHost上(不開啟讀寫分離)。

balance="1"：讀請求隨機分發到當前writeHost對應的readHost和standby的writeHost上。

balance="2"：讀請求隨機分發到當前dataHost內所有的writeHost和readHost上。

balance="3"：讀請求隨機分發到當前writeHost對應的readHost上。

mysql> show @@heartbeat;
+--------+-------+-----------+------+---------+-------+--------+---------+--------------+---------------------+-------+
| NAME   | TYPE  | HOST      | PORT | RS_CODE | RETRY | STATUS | TIMEOUT | EXECUTE_TIME | LAST_ACTIVE_TIME    | STOP  |
+--------+-------+-----------+------+---------+-------+--------+---------+--------------+---------------------+-------+
| hostM1 | mysql | 127.0.0.1 | 3306 |       1 |     0 | idle   |       0 | 1,1,1        | 2018-09-05 16:44:36 | false |
| hostS2 | mysql | 127.0.0.1 | 3307 |       1 |     0 | idle   |       0 | 0,0,0        | 2018-09-05 16:44:36 | false |
+--------+-------+-----------+------+---------+-------+--------+---------+--------------+---------------------+-------+
2 rows in set (0.00 sec)
 create table t1 (id bigint not null primary key,user_id varchar(100),date DATE, fee decimal);

我們在主庫：3306 插入數據

insert into t1(id,user_id,date,fee) values(2,@@hostname,20180901,100);

insert into t1(id,user_id,date,fee) values(5000002,@@hostname,20180905,100);

從庫3307插入數據

insert into t1(id,user_id,date,fee) values(3,@@port,20180901,100);

insert into t1(id,user_id,date,fee) values(5000003,@@port,20180905,100);

主庫查看數據：

mysql> select * from t1;
+---------+-------------+------------+------+
| id      | user_id     | date       | fee  |
+---------+-------------+------------+------+
|       2 | anedbtest01 | 2018-09-01 |  100 |
| 5000002 | anedbtest01 | 2018-09-05 |  100 |
+---------+-------------+------------+------+
2 rows in set (0.00 sec)

從庫查看數據：

mysql> select * from t1;
+---------+-------------+------------+------+
| id      | user_id     | date       | fee  |
+---------+-------------+------------+------+
|       2 | anedbtest01 | 2018-09-01 |  100 |
|       3 | 3307        | 2018-09-01 |  100 |
| 5000002 | anedbtest01 | 2018-09-05 |  100 |
| 5000003 | 3307        | 2018-09-05 |  100 |
+---------+-------------+------------+------+
4 rows in set (0.00 sec)

通過mycat查看數據可以發現,查看的數據是從庫的數據,實現了讀寫分離：

[root@anedbtest01 bin]# /mnt/mysql5641/bin/mysql -uroot -p123 -P8066 -h127.0.0.1
mysql> select * from t1;
+---------+-------------+------------+------+
| id      | user_id     | date       | fee  |
+---------+-------------+------------+------+
|       2 | anedbtest01 | 2018-09-01 |  100 |
|       3 | 3307        | 2018-09-01 |  100 |
| 5000002 | anedbtest01 | 2018-09-05 |  100 |
| 5000003 | 3307        | 2018-09-05 |  100 |
+---------+-------------+------------+------+
4 rows in set (0.00 sec)

修改 schema.xml 中balance="2" ,在mycat端查詢，可以看到有時候查詢會落到主庫，有時候查詢會落到在從庫

 [root@anedbtest01 bin]# /mnt/mysql5641/bin/mysql -uroot -p123 -P8066 -h127.0.0.1
 mysql> select * from t1;
+---------+-------------+------------+------+
| id      | user_id     | date       | fee  |
+---------+-------------+------------+------+
|       2 | anedbtest01 | 2018-09-01 |  100 |
|       3 | 3307        | 2018-09-01 |  100 |
| 5000002 | anedbtest01 | 2018-09-05 |  100 |
| 5000003 | 3307        | 2018-09-05 |  100 |
+---------+-------------+------------+------+
4 rows in set (0.00 sec)
mysql> select * from t1;
+---------+-------------+------------+------+
| id      | user_id     | date       | fee  |
+---------+-------------+------------+------+
|       2 | anedbtest01 | 2018-09-01 |  100 |
| 5000002 | anedbtest01 | 2018-09-05 |  100 |
+---------+-------------+------------+------+
2 rows in set (0.01 sec)

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