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背景
在GreatSQL主从复制环境中，有时候可能会出现一些误操作，将本应该写入到主库的数据写入到了从库，导致主从数据不一致，影响数据同步。是否可以将写入从库的数据同步写入主库呢？
测试环境
| 角色 | IP地址 | 数据库开放端口 | 版本 |
|---|---|---|---|
| 主库 | 192.168.137.179 | 3308 | GreatSQL 8.0.32 |
| 从库 | 192.168.137.180 | 3308 | GreatSQL 8.0.32 |
复制链路：
greatsql> show slave status\G;
*************************** 1. row ***************************Slave_IO_State: Waiting for source to send eventMaster_Host: 192.168.137.179Master_User: rootMaster_Port: 3308Connect_Retry: 60Master_Log_File: binlog.000001Read_Master_Log_Pos: 157Relay_Log_File: oracle_dts-relay-bin.000002Relay_Log_Pos: 367Relay_Master_Log_File: binlog.000001Slave_IO_Running: YesSlave_SQL_Running: Yes表数据
主库
greatsql> select * from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
| 60 | it | 成都 |
+--------+------------+----------+
5 rows in set (0.00 sec)greatsql> insert into dept select 70,'IT','CTU';
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0greatsql> commit;
Query OK, 0 rows affected (0.00 sec)从库
greatsql> select * from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
| 60 | it | 成都 |
| 70 | IT | CTU |
+--------+------------+----------+
6 rows in set (0.00 sec)主库写入的数据正常同步到从库
在从库写入数据
greatsql> insert into dept select 80,'IT','SZ';
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0greatsql> insert into dept select 90,'SALES','SZ';
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0从库数据
greatsql> select * from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
| 60 | it | 成都 |
| 70 | IT | CTU |
| 80 | IT | SZ |
| 90 | SALES | SZ |
+--------+------------+----------+
8 rows in set (0.00 sec)主库数据
greatsql> select * from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
| 60 | it | 成都 |
| 70 | IT | CTU |
+--------+------------+----------+
6 rows in set (0.01 sec)此时从库写入的数据在主库中并没有出现
解析从库的二进制日志
$ mysqlbinlog -vv --base64-output=decode-rows binlog.000002>b002.sqlBEGIN
/*!*/;#at 354
#240221 16:10:25 server id 18001 end_log_pos 416 CRC32 0xcc81584b Table_map: `scott`.`dept` mapped to number 101
#has_generated_invisible_primary_key=0
#at 416
#240221 16:10:25 server id 18001 end_log_pos 462 CRC32 0x5149e38a Write_rows: table id 101 flags:STMT_END_F###INSERT INTO `scott`.`dept`
###SET
###@1=80 /* INT meta=0 nullable=0 is_null=0 */
###@2='IT' /* VARSTRING(56) meta=56 nullable=1 is_null=0 */
###@3='SZ' /* VARSTRING(52) meta=52 nullable=1 is_null=0 */
#at 462
#240221 16:10:25 server id 18001 end_log_pos 493 CRC32 0xab795e4a Xid = 34可以看到写入的从库写入的数据在 binlog.000002，我们可以通过 grep 从库的 server id 确定日志文件中有没有在从库写入的数据。
复制从库日志到主库
$ scp binlog.000002 192.168.137.179:/tmp/
Warning: Permanently added '192.168.137.179' (ECDSA) to the list of known hosts.
root@192.168.137.179's password:
binlog.000002 100% 836 1.1MB/s 00:00 应用从库的二进制日志
应用从库的日志到主库
$ mysqlbinlog binlog.000002|mysql -uroot -p -h127.1 -P3308主库应用从库二进制日志时，从库二进制日志信息未发生变化
greatsql> show binary logs;
+---------------+-----------+-----------+
| Log_name | File_size | Encrypted |
+---------------+-----------+-----------+
| binlog.000001 | 498 | No |
| binlog.000002 | 836 | No |
| binlog.000003 | 237 | No |
+---------------+-----------+-----------+
3 rows in set (0.00 sec)主从复制链路状态正常
greatsql> show slave status\G;
*************************** 1. row ***************************Slave_IO_State: Waiting for source to send eventMaster_Host: 192.168.137.179Master_User: rootMaster_Port: 3308Connect_Retry: 60Master_Log_File: binlog.000001Read_Master_Log_Pos: 1059Relay_Log_File: oracle_dts-relay-bin.000002Relay_Log_Pos: 1269Relay_Master_Log_File: binlog.000001Slave_IO_Running: YesSlave_SQL_Running: Yes可以看到主库在应用从库产生的二进制日志时，从库没有重复应用这些二进制日志(By default, the replication I/O (receiver) thread does not write binary log events to the relay log if they have the replica's server ID (this optimization helps save disk usage). )，出现主键冲突，导致复制状态出错
查看主库数据
greatsql> select * from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
| 60 | it | 成都 |
| 70 | IT | CTU |
| 80 | IT | SZ |
| 90 | SALES | SZ |
+--------+------------+----------+
8 rows in set (0.00 sec)后续测试，主库写入数据可正常同步到从库。
Enjoy GreatSQL :)
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