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
复制链路：
greatsql> show slave status\G;*************************** 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
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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)
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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)
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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: 0
greatsql> insert into dept select 90,'SALES','SZ';Query OK, 1 row affected (0.01 sec)Records: 1 Duplicates: 0 Warnings: 0
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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)
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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)
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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
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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
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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
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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)
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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 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
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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)
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后续测试，主库写入数据可正常同步到从库。
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