Mycat分库分表实时同步到GreatSQL

这个事情怎么产生的

MyCat作为经典的分库分表中间件，在长时间内被广泛认为是管理超大MySQL数据库集合的有效解决方案。近来接到客户需求，需要将MyCat集群迁移到GreatSQL中，并且在一段时间内需要实时从MyCat中同步数据到GreatSQL中，全量同步数据比较容易操作，增量同步有如下两个棘手的问题：

1. 多个server，不同的库名字，都要同步到GreatSQL一个库中，即同步关系如下

server1:db1.tab->gdb:db.tab; server2:db2.tab->gdb:db.tab; server3:db3.tab->gdb:db.tab; 

2. ddl同步多次执行会冲突。当MyCat的表中添加一个索引、添加一个字段时，实际上是后端所有db都会执行这个DDL，同步到GreatSQL时，多次执行DDL，复制会异常中断。

为了解决上面两个问题，经过查询资料，发现有两个不常用，官方也不建议使用的功能，刚好能够满足需求

1. 为解决库名映射问题：需要在配置文件中添加参数

replicate_rewrite_db="channel_1:test_rep1->test_rep" replicate_rewrite_db="channel_2:test_rep2->test_rep" replicate_rewrite_db="channel_3:test_rep3->test_rep" 

2. 为了解决DDL同步后重复执行导致复制中断问题，在配置文件中添加

slave-skip-errors=ddl_exist_errors 

验证一下

为了简化问题，MyCat集群咱们就不搭建了，简化为多源同步复制问题。

1.初始化4个实例，同步关系如下

源端口	源DB_NAME	目标端口	目标映射DB	channel_name
3306	test_rep1	3309	test_rep	channel_3306
3307	test_rep2	3309	test_rep	channel_3307
3308	test_rep3	3309	test_rep	channel_3308

2.在3309的实例配置文件中，添加库映射关系配置和DDL冲突忽略参数

replicate_rewrite_db="channel_3306:test_rep1->test_rep" replicate_rewrite_db="channel_3307:test_rep2->test_rep" replicate_rewrite_db="channel_3308:test_rep3->test_rep" slave-skip-errors=ddl_exist_errors 

4.在3309实例中，配置三个channel

greatsql> change master to MASTER_HOST = '172.17.137.91',MASTER_USER = 'greatsql',MASTER_PASSWORD = 'greatsql',MASTER_PORT = 3306,MASTER_AUTO_POSITION = 1 FOR CHANNEL 'channel_3306'; greatsql> change master to MASTER_HOST = '172.17.137.91',MASTER_USER = 'greatsql',MASTER_PASSWORD = 'greatsql',MASTER_PORT = 3307,MASTER_AUTO_POSITION = 1 FOR CHANNEL 'channel_3307'; greatsql> change master to MASTER_HOST = '172.17.137.91',MASTER_USER = 'greatsql',MASTER_PASSWORD = 'greatsql',MASTER_PORT = 3308,MASTER_AUTO_POSITION = 1 FOR CHANNEL 'channel_3308'; greatsql> start slave; 

3.检查channel配置状态

greatsql> show slave status \G *************************** 1. row *************************** Slave_IO_State: Waiting for source to send event Master_Host: 172.17.137.91 Master_User: greatsql Master_Port: 3306 Connect_Retry: 60 Master_Log_File: binlog.000002 Read_Master_Log_Pos: 1119 Relay_Log_File: relaylog-channel_3306.000007 Relay_Log_Pos: 397 Relay_Master_Log_File: binlog.000002 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 1119 Relay_Log_Space: 606 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0 Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 0 Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 3306 Master_UUID: 5facacd7-9ed6-11ee-b76b-00163e5af5d6 Master_Info_File: mysql.slave_master_info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Replica has read all relay log; waiting for more updates Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: 49b66af0-9ed6-11ee-ae4f-00163e5af5d6:3, 5a369d0b-9ed6-11ee-b3d1-00163e5af5d6:3, 5facacd7-9ed6-11ee-b76b-00163e5af5d6:1-4, 9a5f9c26-4262-11ee-85fd-00163e5af5d6:1-16571224 Auto_Position: 1 Replicate_Rewrite_DB: (test_rep1,test_rep) Channel_Name: channel_3306 Master_TLS_Version: Master_public_key_path: Get_master_public_key: 0 Network_Namespace: *************************** 2. row *************************** Slave_IO_State: Waiting for source to send event Master_Host: 172.17.137.91 Master_User: greatsql Master_Port: 3307 Connect_Retry: 60 Master_Log_File: binlog.000002 Read_Master_Log_Pos: 1119 Relay_Log_File: relaylog-channel_3307.000004 Relay_Log_Pos: 1034 Relay_Master_Log_File: binlog.000002 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 1119 Relay_Log_Space: 1243 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0 Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 0 Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 3307 Master_UUID: 5a369d0b-9ed6-11ee-b3d1-00163e5af5d6 Master_Info_File: mysql.slave_master_info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Replica has read all relay log; waiting for more updates Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: 5a369d0b-9ed6-11ee-b3d1-00163e5af5d6:1-2:4 Executed_Gtid_Set: 49b66af0-9ed6-11ee-ae4f-00163e5af5d6:3, 5a369d0b-9ed6-11ee-b3d1-00163e5af5d6:3, 5facacd7-9ed6-11ee-b76b-00163e5af5d6:1-4, 9a5f9c26-4262-11ee-85fd-00163e5af5d6:1-16571224 Auto_Position: 1 Replicate_Rewrite_DB: (test_rep2,test_rep) Channel_Name: channel_3307 Master_TLS_Version: Master_public_key_path: Get_master_public_key: 0 Network_Namespace: *************************** 3. row *************************** Slave_IO_State: Waiting for source to send event Master_Host: 172.17.137.91 Master_User: greatsql Master_Port: 3308 Connect_Retry: 60 Master_Log_File: binlog.000002 Read_Master_Log_Pos: 1119 Relay_Log_File: relaylog-channel_3308.000004 Relay_Log_Pos: 1034 Relay_Master_Log_File: binlog.000002 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 1119 Relay_Log_Space: 1243 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0 Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 0 Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 3308 Master_UUID: 49b66af0-9ed6-11ee-ae4f-00163e5af5d6 Master_Info_File: mysql.slave_master_info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Replica has read all relay log; waiting for more updates Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: 49b66af0-9ed6-11ee-ae4f-00163e5af5d6:1-2:4 Executed_Gtid_Set: 49b66af0-9ed6-11ee-ae4f-00163e5af5d6:3, 5a369d0b-9ed6-11ee-b3d1-00163e5af5d6:3, 5facacd7-9ed6-11ee-b76b-00163e5af5d6:1-4, 9a5f9c26-4262-11ee-85fd-00163e5af5d6:1-16571224 Auto_Position: 1 Replicate_Rewrite_DB: (test_rep3,test_rep) Channel_Name: channel_3308 Master_TLS_Version: Master_public_key_path: Get_master_public_key: 0 Network_Namespace: 3 rows in set, 1 warning (0.00 sec) 

在上面的输出中，可以重点关注如下字段信息，说明db转换映射成功

$ MYSQL_PWD=greatsql mysql -ugreatsql -h127.0.0.1 -P3309 -e 'show replica status \G'| grep -wE 'Replica_IO_Running|Replica_SQL_Running|Replicate_Rewrite_DB|Channel_Name' Replica_IO_Running: Yes Replica_SQL_Running: Yes Replicate_Rewrite_DB: (test_rep1,test_rep) Channel_Name: channel_3306 Replica_IO_Running: Yes Replica_SQL_Running: Yes Replicate_Rewrite_DB: (test_rep2,test_rep) Channel_Name: channel_3307 Replica_IO_Running: Yes Replica_SQL_Running: Yes Replicate_Rewrite_DB: (test_rep3,test_rep) Channel_Name: channel_3308 

在3309实例中，查询replica_skip_errors，确认复制异常跳过的错误码，设置为ddl_exist_errors会自动转换为如下错误码

greatsql> select @@replica_skip_errors; +---------------------------------------------------+ | @@replica_skip_errors | +---------------------------------------------------+ | 1007,1008,1050,1051,1054,1060,1061,1068,1091,1146 | +---------------------------------------------------+ 1 row in set (0.00 sec) 

5.数据同步验证

1. 在3309库中，创建database test_rep

这个库需要手动创建，是测试发现映射关系只对库下面的表生效，库不会自动转换创建。

2. 在3306库中，创建database test_rep1，并且创建tab1表

$ mysql -ugreatsql -h127.0.0.1 -p -P3306 -s greatsql> create database test_rep1; greatsql> use test_rep1; greatsql> create table tab1(id int primary key auto_increment, cname varchar(10), age int); 

3. 在3307库中，创建database test_rep2，并且创建tab1表

$ mysql -ugreatsql -h127.0.0.1 -p -P3307 -s greatsql> create database test_rep2; greatsql> use test_rep2; greatsql> create table tab1(id int primary key auto_increment, cname varchar(10), age int); 

4. 在3308库中，创建database test_rep3，并且创建tab1表

$ mysql -ugreatsql -h127.0.0.1 -p -P3308 -s greatsql> create database test_rep3; greatsql> use test_rep3; greatsql> create table tab1(id int primary key auto_increment, cname varchar(10), age int); 

5. 在3309中确认database及表的同步

$ mysql -ugreatsql -h127.0.0.1 -p -P3309 -s greatsql> show databases; Database information_schema mysql performance_schema sys test_db test_rep test_rep1 test_rep2 test_rep3 greatsql> show tables from test_rep; Tables_in_test_rep tab1 greatsql> show tables from test_rep1; greatsql> show tables from test_rep2; greatsql> show tables from test_rep3; 

从上面的信息可以看出，在3309中，3306、3307、3308中创建的库均按照原有的名字进行了同步，但是表只同步在了3309映射的库test_rep中。

6. 分别在3306、3307、3308中插入一条记录

3306 : insert into test_rep1.tab1 values(1,'a',10); 3307 : insert into test_rep2.tab1 values(2,'b',20); 3308 : insert into test_rep3.tab1 values(3,'c',30); 

然后在各自节点查询数据插入情况

$ mysql -ugreatsql -h127.0.0.1 -p -P3306 -s test_rep1 -e 'select * from tab1' id cname age 1 a 10 $ mysql -ugreatsql -h127.0.0.1 -p -P3307 -s test_rep2 -e 'select * from tab1' id cname age 2 b 20 $ mysql -ugreatsql -h127.0.0.1 -p -P3308 -s test_rep3 -e 'select * from tab1' id cname age 3 c 30 $ mysql -ugreatsql -h127.0.0.1 -p -P3309 -s test_rep -e 'select * from tab1' id cname age 1 a 10 2 b 20 3 c 30 $ mysql -ugreatsql -h127.0.0.1 -p -P3309 -s test_rep1 -e 'select * from tab1' ERROR 1146 (42S02) at line 1: Table 'test_rep1.tab1' doesn't exist $ mysql -ugreatsql -h127.0.0.1 -p -P3309 -s test_rep2 -e 'select * from tab1' ERROR 1146 (42S02) at line 1: Table 'test_rep2.tab1' doesn't exist $ mysql -ugreatsql -h127.0.0.1 -p -P3309 -s test_rep3 -e 'select * from tab1' ERROR 1146 (42S02) at line 1: Table 'test_rep3.tab1' doesn't exist 

从上面的查询情况可以看出，3306、3307、3308节点中只有一条记录，并且记录都被同步到了3309的test_rep.tab1表中，而且在3309的test_rep1、test_rep2、test_rep3中是没有表存在的。

7. 分别在3306、3307、3308给表tab创建一个索引

greatsql> alter table tab1 add index idx_cname(cname); 

8. 观察3309中表的索引情况，可以看到索引idx_cname被同步过来了

$ mysql -ugreatsql -h127.0.0.1 -p -P3309 -s greatsql> use test_rep greatsql> show create table tab1 \G *************************** 1. row *************************** Table: tab1 Create Table: CREATE TABLE `tab1` ( `id` int NOT NULL AUTO_INCREMENT, `cname` varchar(10) COLLATE utf8mb4_unicode_ci DEFAULT NULL, `age` int DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_cname` (`cname`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci 1 row in set (0.00 sec) 

9. 分别在3306、3307、3308做update、delete操作

greatsql> update test_rep1.tab1 set age=110 where id=1; greatsql> update test_rep2.tab1 set age=120 where id=2; greatsql> update test_rep3.tab1 set age=130 where id=3; greatsql> delete from test_rep1.tab1 where id=1; greatsql> delete from test_rep2.tab1 where id=1; greatsql> delete from test_rep3.tab1 where id=1; 

查看3309的数据同步情况，确认数据被清理

$ mysql -ugreatsql -h127.0.0.1 -p -P3309 -s Welcome to the MySQL monitor. Commands end with ; or \g. greatsql> select * from test_rep.tab1; 

10. 观察3个channel的同步情况，可以确认三个复制同步均正常

$ mysql -ugreatsql -h127.0.0.1 -p -P3309 -e 'show replica status \G'| grep -E 'Replica_IO_Running|Replica_SQL_Running|Channel_Name' greatsql: [Warning] Using a password on the command line interface can be insecure. Replica_IO_Running: Yes Replica_SQL_Running: Yes Replica_SQL_Running_State: Replica has read all relay log; waiting for more updates Channel_Name: channel_3306 Replica_IO_Running: Yes Replica_SQL_Running: Yes Replica_SQL_Running_State: Replica has read all relay log; waiting for more updates Channel_Name: channel_3307 Replica_IO_Running: Yes Replica_SQL_Running: Yes Replica_SQL_Running_State: Replica has read all relay log; waiting for more updates Channel_Name: channel_3308 

至此dml、ddl同步均验证。

方案缺陷

1. 本方案中，业务访问MyCat的表名字，和server后端的表名字完全一致，只是库名字不相同，然后MyCat代理表名和实际server的表名字可以不相同，这种情况下，暂时无法映射处理
2. MyCat代理的实际上是多个单独的库，如果这些库之前没有做自增主键步长处理，或者其他一些主键不重复策略，同步过程中，会存在主键冲突导致数据同步中断的情况，需要提前准备处理方案。

最后附上参考资料

• https://dev.mysql.com/doc/refman/8.0/en/replication-options-replica.html#option_mysqld_replicate-rewrite-db

• https://dev.mysql.com/doc/refman/8.0/en/replication-options-replica.html#option_mysqld_slave-skip-errors

Enjoy GreatSQL :)

---

关于GreatSQL

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关于 GreatSQL

GreatSQL是适用于金融级应用的国内自主开源数据库，具备高性能、高可靠、高易用性、高安全等多个核心特性，可以作为MySQL或Percona Server的可选替换，用于线上生产环境，且完全免费并兼容MySQL或Percona Server。

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