【MySQL】重放binlog故障一则 ERROR 1050 (42S01) : Table '' already exists
〇 现象:
在通过binlog增量恢复数据时,报错1050。
〇 版本:
MySQL 5.5.x 及以下 ,低版本的MySQL 5.6.x (在5.6的高版本中测试,无法复现,疑似被修复)
〇 原因:
binlog记录了执行出错的DDL语句,此处,具体DDL是CREATE VIEW $view_name AS ...
有点奇怪,难道执行错误了的DDL也会被记录到binlog中么?
〇 复现:
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[17:52:45] root@localhost [a]> FLUSH LOGS;
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Query OK, 0 rows affected (0.01 sec)
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[17:52:47] root@localhost [a]> SHOW BINLOG EVENTS IN 'mysql55-bin.000006';
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+--------------------+-----+-------------+-----------+-------------+---------------------------------------+
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| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
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+--------------------+-----+-------------+-----------+-------------+---------------------------------------+
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| mysql55-bin.000006 | 4 | Format_desc | 55 | 107 | Server ver: 5.5.57-log, Binlog ver: 4 |
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+--------------------+-----+-------------+-----------+-------------+---------------------------------------+
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1 row in set (0.00 sec)
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[17:53:13] root@localhost [a]> CREATE TABLE t(id int);
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Query OK, 0 rows affected (0.01 sec)
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[17:53:18] root@localhost [a]> CREATE VIEW v_t AS SELECT * from t;
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Query OK, 0 rows affected (0.00 sec)
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[17:53:21] root@localhost [a]> CREATE VIEW v_t AS SELECT * from t;
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ERROR 1050 (42S01): Table 'v_t' already exists
此时,再次检查binlog:
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[17:53:24] root@localhost [a]> SHOW BINLOG EVENTS IN 'mysql55-bin.000006'/G
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*************************** 1. row ***************************
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Log_name: mysql55-bin.000006
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Pos: 4
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Event_type: Format_desc
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Server_id: 55
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End_log_pos: 107
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Info: Server ver: 5.5.57-log, Binlog ver: 4
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*************************** 2. row ***************************
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Log_name: mysql55-bin.000006
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Pos: 107
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Event_type: Query
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Server_id: 55
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End_log_pos: 189
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Info: use `a`; CREATE TABLE t(id int)
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*************************** 3. row ***************************
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Log_name: mysql55-bin.000006
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Pos: 189
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Event_type: Query
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Server_id: 55
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End_log_pos: 369
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Info: use `a`; CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v_t` AS SELECT * from t
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*************************** 4. row ***************************
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Log_name: mysql55-bin.000006
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Pos: 369
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Event_type: Query
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Server_id: 55
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End_log_pos: 549
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Info: use `a`; CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v_t` AS SELECT * from t
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4 rows in set (0.00 sec)
可以发现,第二次执行CREATE VIEW,即便在mysql client执行时报错,也被记录到binlog中。
自然,在通过mysqlbinlog重放binlog时,也会报错。
但在复制结构中,从实例不会重放该events,故从库不会报错。
重新通过mysqlbinlog解析日志得到:
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# at 107
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#180206 17:53:18 server id 55 end_log_pos 189 Query thread_id=13 exec_time=0 error_code=0
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use `a`/*!*/;
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SET TIMESTAMP=1517910798/*!*/;
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SET @@session.pseudo_thread_id=13/*!*/;
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SET @@session.foreign_key_checks=1, @@session.sql_auto_is_null=0, @@session.unique_checks=1, @@session.autocommit=1/*!*/;
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SET @@session.sql_mode=0/*!*/;
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SET @@session.auto_increment_increment=1, @@session.auto_increment_offset=1/*!*/;
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/*!/C utf8 *//*!*/;
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SET @@session.character_set_client=33,@@session.collation_connection=33,@@session.collation_server=8/*!*/;
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SET @@session.lc_time_names=0/*!*/;
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SET @@session.collation_database=DEFAULT/*!*/;
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CREATE TABLE t(id int)
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/*!*/;
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# at 189
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#180206 17:53:21 server id 55 end_log_pos 369 Query thread_id=13 exec_time=0 error_code=0
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SET TIMESTAMP=1517910801/*!*/;
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CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v_t` AS SELECT * from t
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/*!*/;
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# at 369
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#180206 17:53:22 server id 55 end_log_pos 549 Query thread_id=13 exec_time=0 error_code=1050
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SET TIMESTAMP=1517910802/*!*/;
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CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v_t` AS SELECT * from t
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/*!*/;
可以发现第二次报错的语句,虽然被记录到binlog中,但error_code标识为1050
至于为何从库不报错,大概是因为sql thread会特殊处理这种error_code,不会执行。
而mysqlbinlog mysql-binlog.00000x | mysql -u -p -S 重放binlog的方式会报错。——大概是因为mysql这个client工具没有做对mysqlbinlog解析出来的error_code的特殊处理吧。
暂时不知道是否为bug,但高版本的MySQL5.6.x已经修正了该问题,5.7也如此。
因此,在可能出现问题的版本,通过binlog增量恢复数据时,可能需要特殊处理。
正文到此结束