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高效数据流转：Mycat分库分表与GreatSQL实时同步

2024-01-09 08:37:05 作者：GreatSQL

聚焦数据库扩容与实时数据同步,探索MyCat分库分表与GreatSQL的强大结合！想在大规模数据处理中游刃有余？本指南将带你轻松掌握MyCat的分布式解决方案和GreatSQL的实时同步机制,让高效、稳定的数据库管理触手可及,一起揭开高并发环境下数据库优化的神秘面纱吧！

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_errors

3.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;

4.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);

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);

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);

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。

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。

分别在3306、3307、3308给表tab创建一个索引

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

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)

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;

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

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