Mysql slave是否可以update ?
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最近平台要做迁移,由于业务迁移过程需求,希望slave在平台迁移过程中,既能保证master的数据同步到slave,但是也希望slave可以update.
这个需求,作为DBA,单单从数据库层面,基本可以判断,是不可行的.但是,实际测试,才有说服力.用数据/实验结果说话。
开始着手搭建一个测试的主从,进行slave的update测试.
- 将slave的read_only设置为on,让slave是可以更改的.这里需要注意.read_only这个参数.对于root或者拥有(.) 全instance权限的用户,是不生效的.
- 主库创建一个测试表test2
-
在slave上,可以看到test2已经同步过来
查询表行数mysql> select count(*) from test2; +----------+ | count(*) | +----------+ | 23502 | +----------+ 1 row in set (0.01 sec) -
删除10行
mysql> delete from test2 where id<10; Query OK, 9 rows affected (0.04 sec) - 再次查询表行数
mysql> select count(*) from test2; +----------+ | count(*) | +----------+ | 23493 | +----------+ 1 row in set (0.01 sec) - 在主库,修改表数据
mysql> select count(*) from test2; +----------+ | count(*) | +----------+ | 23502 | +----------+ 1 row in set (0.01 sec) - 删除5行数据
mysql> delete from test2 where id<5; Query OK, 4 rows affected (0.04 sec) - 查询行数
mysql> select count(*) from test2; +----------+ | count(*) | +----------+ | 23498 | +----------+ 1 row in set (0.01 sec) -
再到备库,查看同步状态
mysql> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 10.27.20.4 Master_User: envision Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000043 Read_Master_Log_Pos: 57380204 Relay_Log_File: replay-bin.000003 Relay_Log_Pos: 320 Relay_Master_Log_File: mysql-bin.000043 Slave_IO_Running: Yes Slave_SQL_Running: No Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 1032 Last_Error: Could not execute Delete_rows event on table cnpmjs.test2; Can't find record in 'test2', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000043, end_log_pos 57380173 Skip_Counter: 0 Exec_Master_Log_Pos: 57375790 Relay_Log_Space: 13539720 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: NULL Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 1032 Last_SQL_Error: Could not execute Delete_rows event on table cnpmjs.test2; Can't find record in 'test2', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000043, end_log_pos 57380173 Replicate_Ignore_Server_Ids: Master_Server_Id: 102 Master_UUID: b095e989-7dcf-11e8-83a2-0017fa032e39 Master_Info_File: /var/lib/mysql/master.info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: 180702 14:54:00 Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0 Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version: 1 row in set (0.00 sec)上面错误,已经说明,主从的数据已经不一致,无法继续同步
- 在slave上修复数据,插入缺少的10行
mysql> insert into test2 select * from user where id<10; Query OK, 9 rows affected (0.01 sec) Records: 9 Duplicates: 0 Warnings: 0 - 修改完成之后,重启slave进程
mysql> stop slave; Query OK, 0 rows affected (0.00 sec) mysql> start slave; Query OK, 0 rows affected (0.01 sec) - 再次查询,可以看到,slave又继续同步了.
mysql> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 10.27.20.4 Master_User: envision Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000043 Read_Master_Log_Pos: 57380204 Relay_Log_File: replay-bin.000005 Relay_Log_Pos: 320 Relay_Master_Log_File: mysql-bin.000043 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: 57380204 Relay_Log_Space: 688 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: 102 Master_UUID: b095e989-7dcf-11e8-83a2-0017fa032e39 Master_Info_File: /var/lib/mysql/master.info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Slave 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: Auto_Position: 0 Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version: 1 row in set (0.00 sec) - 查询数据,也是主库删除5条之后的信息.
mysql> select count(*) from test2; +----------+ | count(*) | +----------+ | 23498 | +----------+ 1 row in set (0.01 sec) - 再次更新master,看主从同步情况
mysql> insert into test2 select * from test2; Query OK, 23498 rows affected (1.01 sec) Records: 23498 Duplicates: 0 Warnings: 0 - 查询主库表的行数
mysql> select count(*) from test2; +----------+ | count(*) | +----------+ | 46996 | +----------+ 1 row in set (0.02 sec) - 从库查询,同步正常执行.
mysql> select count(*) from test2; +----------+ | count(*) | +----------+ | 46996 | +----------+ 1 row in set (0.02 sec)前面测试的是delete,现在测试update是否可行
- 在备库,修改数据
mysql> update test2 set json=0 where id=5; Query OK, 2 rows affected (0.08 sec) Rows matched: 2 Changed: 2 Warnings: 0 mysql> select * from test2 where id=5\G; *************************** 1. row *************************** id: 5 gmt_create: 2016-02-23 12:28:51 gmt_modified: 2016-02-23 12:28:51 name: m_gol salt: 0 password_sha: 0 ip: 0 roles: [] rev: 2-379c3d7dfc06312105072ec0ccf84b4a email: m.goleb@gmail.com json: 0 npm_user: 1 - 在主库,修改数据
mysql> update test2 set json=1000 where id=5; Query OK, 0 rows affected (0.07 sec) Rows matched: 2 Changed: 0 Warnings: 0 mysql> select * from test2 where id=5\G; *************************** 1. row *************************** id: 5 gmt_create: 2016-02-23 12:28:51 gmt_modified: 2016-02-23 12:28:51 name: m_gol salt: 0 password_sha: 0 ip: 0 roles: [] rev: 2-379c3d7dfc06312105072ec0ccf84b4a email: m.goleb@gmail.com json: 1000 npm_user: 1 - 在备库查询slave同步状态
mysql> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 10.27.20.4 Master_User: envision Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000043 Read_Master_Log_Pos: 70913715 Relay_Log_File: replay-bin.000005 Relay_Log_Pos: 13529969 Relay_Master_Log_File: mysql-bin.000043 Slave_IO_Running: Yes Slave_SQL_Running: No Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 1032 Last_Error: Could not execute Update_rows event on table cnpmjs.test2; Can't find record in 'test2', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000043, end_log_pos 70912987 Skip_Counter: 0 Exec_Master_Log_Pos: 70909853 Relay_Log_Space: 13534935 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: NULL Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 1032 Last_SQL_Error: Could not execute Update_rows event on table cnpmjs.test2; Can't find record in 'test2', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000043, end_log_pos 70912987 Replicate_Ignore_Server_Ids: Master_Server_Id: 102 Master_UUID: b095e989-7dcf-11e8-83a2-0017fa032e39 Master_Info_File: /var/lib/mysql/master.info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: 180702 15:23:42 Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0 Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version: 1 row in set (0.00 sec)总结, slave是不能修改的,尤其是在相同的表,和相同的行,如果出现查找的行不存在.就会导致同步失败.
即使,不是delete,只是update,也是不可以的.
所以slave还是需要以read_only的形式存在. 才能保证组从一直正常同步.
原因是，binglog中，是记录行信息的上下文的，如果上下文对不上了（在slave端被修改过），接下来的binglog的recover就不能正确找到需要继续还原的信息，也就不能成功执行recover，进而导致slave同步失败。
参考下面一段binlog的截取信息：
mysqlbinlog mysql-bin.000005 >> test.log
#181126 9:53:49 server id 101 end_log_pos 8342676 CRC32 0x928e28de Anonymous_GTID last_committed=2436 sequence_number=2437 rbr_only=yes
;
SET @@SESSION.GTID_NEXT= 'ANONYMOUS';
# at 8342676
#181126 9:53:49 server id 101 end_log_pos 8342758 CRC32 0x1068a385 Query thread_id=58717 exec_time=0 error_code=0
SET TIMESTAMP=1543226029;
BEGIN
;
# at 8342758
#181126 9:53:49 server id 101 end_log_pos 8342849 CRC32 0x2ee04d35 Table_map: `test`.`app_purchases` mapped to number 290
# at 8342849
#181126 9:53:49 server id 101 end_log_pos 8343168 CRC32 0x598ec3d0 Update_rows: table id 290 flags: STMT_END_F
BINLOG '
rcL7WxNlAAAAWwAAAEFNfwAAACIBAAAAAAEADmVvc19wb3J0YWxfd2ViAA1hcHBfcHVyY2hhc2Vz
AAsPDw8PAQ8SEhESAQ7AAMAAwADAAP0CAAAAAPgHNU3gLg==
rcL7Wx9lAAAAPwEAAIBOfwAAACIBAAAAAAEAAgAL/////2D7JDBlM2FmNzJkLWIxNDctNGQ3My1h
ZjY5LTBhNDQxZmZmMTdiMSQzN2Q2ZDJjZS1hZGU2LTRhNzEtOTEzYS1lNDJhMTQ5NmQxMDAPbzE1
NDI1MjM2NjI4NDcxJDM3ZDZkMmNlLWFkZTYtNGE3MWQ5ZDc1NWUyLWJmYTQtNDA3ZgKZoXSdawBg
+CQwZTNhZjcyZC1iMTQ3LTRkNzMtYWY2OS0wYTQ0MWZmZjE3YjEkMzdkNmQyY2UtYWRlNi00YTcx
LTkxM2EtZTQyYTE0OTZkMTAwD28xNTQyNTIzNjYyODQ3MSQzN2Q2ZDJjZS1hZGU2LTRhNzFkOWQ3
NTVlMi1iZmE0LTQwN2YCmaF0nWtb+8KtmaF0nXEB0MOOWQ==
';
# at 8343168
#181126 9:53:49 server id 101 end_log_pos 8343199 CRC32 0xcb9106dc Xid = 400668
COMMIT;
# at 8343199免责声明：
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