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 statusG;
*************************** 1. row ***************************
Slave_IO_State: Waiting for source to send event
Master_Host: 192.168.137.179
Master_User: root
Master_Port: 3308
Connect_Retry: 60
Master_Log_File: binlog.000001
Read_Master_Log_Pos: 157
Relay_Log_File: oracle_dts-relay-bin.000002
Relay_Log_Pos: 367
Relay_Master_Log_File: binlog.000001
Slave_IO_Running: Yes
Slave_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: 0
greatsql> commit;
Query OK, 0 rows affected (0.00 sec)
从库
greatsql> select * from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+服务器托管网----------+
| 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 Duplicate服务器托管网s: 0 Warnings: 0
greatsql> 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.sql
BEGIN
/*!*/;
#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 statusG;
*************************** 1. row ***************************
Slave_IO_State: Waiting for source to send event
Master_Host: 192.168.137.179
Master_User: root
Master_Port: 3308
Connect_Retry: 60
Master_Log_File: binlog.000001
Read_Master_Log_Pos: 1059
Relay_Log_File: oracle_dts-relay-bin.000002
Relay_Log_Pos: 1269
Relay_Master_Log_File: binlog.000001
Slave_IO_Running: Yes
Slave_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 🙂
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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