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：
- 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; - 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
- 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" - 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_errors4.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
- 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。
- 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
- 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
- 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
Enjoy GreatSQL :)
关于GreatSQL
GreatSQL数据库是一款开源免费数据库，可在普通硬件上满足金融级应用场景，具有高可用、高性能、高兼容、高安全等特性，可作为MySQL或Percona Server for MySQL的理想可选替换。
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Enjoy GreatSQL :)
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。
相关链接： GreatSQL社区 Gitee GitHub Bilibili
GreatSQL社区：
社区有奖建议反馈： https://greatsql.cn/thread-54-1-1.html
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