《那些年，我在乙方的日子 -- 神谕篇NO1》

某个夏日的午后，窗外知了在大声鸣叫。而我却在睡梦中跟基友一起吃鸡，正准备抢空投时 。手机突然铃声响起，惊醒后一看是领导电话，一下子回到了现实中。心想又得去公司吃 "机" 了。

领导:“神谕，工单积压很多了，你过来帮忙处理下。午睡啊？打车过来，公司全额报销”。

1、max_execution_time 过小导致

mysqldump: Error: Query execution was interrupted, maximum statement execution time exceeded when trying to dump tablespaces OR mysqldump: Error 3024: Query execution was interrupted, maximum statement execution time exceeded when dumping table $tb_name at row: xxxx

版本：MySQL 5.7.8+

原因：max_execution_time过小

处理思路：

① 通过hint，增大N值（文档说，在hint用法中，将N改为0为无限制，但我测下来不生效，可设置成一个较大值如999999解决）SELECT /*+ MAX_EXECUTION_TIME(N) */ * FROM t1 LIMIT 100000; ② 修改max_execution_time值，将该值设置为较大一个值，或设置为0（不限制）

附录：该参数5.7.8被添加，单位为ms，动态参数，默认为0，设置为0时意味着SELECT超时不被设置（不限制超时时间）。不作用于存储过程中的SELECT语句，并且只作用于只读的SELECT，如INSERT ... SELECT ... 是不被作用的。

for more information: http://blog.itpub.net/29773961/viewspace−2150443/

2、关于view引用了无效的表，列，函数或者定义。

mysqldump: Couldnt execute SHOW FIELDS FROM view_name: View db_name.view_name references invalid table(s) or column(s) or function(s) or definerinvoker of view lack rights to use them (1356)

原因：该view引用了无效的表，列，函数或者定义者。

处理思路：可以根据报错信息，进入db，执行SHOW CREATE VIEW view_name\G，查看该view的定义，逐一检查该view的基表，列，或相关函数与用户是否具有相关权限。考虑重建或删除视图。

mysqldump: Couldnt execute show create table view_name: Illegal mix of collations for operation UNION (1271)

原因：创建view时，使用UNION时存在非法的排序规则组合。

处理思路：检查该视图定义，检查字符集，考虑重建或删除视图。

3、关于MySQL字符串大小写

Error: Couldnt read status information for table Income_config ()mysqldump: Couldnt execute show create table Tser_table: Table db_name.test_table doesnt exist (1146) OR mysqldump: Got error: 1049: Unknown database $db_name when selecting the database

原因一：从lower_case_table_names的0设置成1，导致部分原来含有大写字母的库表“找不到”。

处理思路：将lower_case_table_names设置回0。如若有需要将lower_case_table_names设置为1，需先设置为0，并将含有大写字母的库表改成小写，再设置为1。

原因二（MySQL 5.5及以下版本可能出现）：

表损坏导致该表找不到（InnoDB）。frm和ibd文件都在，但无法SHOW CREATE TABLE xxx\G error log一则：

170820 17:44:48 InnoDB: error: space object of table 'db_name/tb_name',
InnoDB: space id 4335 did not exist in memory. Retrying an open.
170820 17:44:48 InnoDB: Error: tablespace id and flags in file './db_name/tb_name.ibd' are 0 and 0, but in the InnoDB
InnoDB: data dictionary they are 4335 and 0.
InnoDB: Have you moved InnoDB .ibd files around without using the
InnoDB: commands DISCARD TABLESPACE and IMPORT TABLESPACE?
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.5/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
170820 17:44:48 InnoDB: cannot calculate statistics for table db_name/tb_name
InnoDB: because the .ibd file is missing. For help, please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.5/en/innodb-troubleshooting.html
170820 17:44:48 [ERROR] MySQL is trying to open a table handle but the .ibd file for
table db_name/tb_name does not exist.
Have you deleted the .ibd file from the database directory under
the MySQL datadir, or have you used DISCARD TABLESPACE?
See http://dev.mysql.com/doc/refman/5.5/en/innodb-troubleshooting.html
how you can resolve the problem.

处理思路：从完整备份+binlog还原，对于有主或从的实例，可考虑通过物理备份还原。

该故障出现的原因可能很多，此处只列出两种。排错思路比较简单，找到这张表或库，并确认能否手动正常访问。

4、max_allowed_packet设置过小

mysqldump: Error 2020: Got packet bigger than max_allowed_packet bytes when dumping table tb_name at row: xxxx

原因：默认的max_allowed_packet过小

处理思路：在mysqldump时增加max_allowed_packet的大小，如mysqldump --max-allowed-packet=268435456

5、备份期间执行DDL

mysqldump: Error 1412: Table definition has changed, please retry transaction when dumping table tb_name at row: 0

原因：在备份该表时，表定义被修改。FLUSH TABLE WITH READ LOCK只保证数据一致性，并不保证schema不被修改。

处理思路：备份时期不做DDL操作。

复现一：

session1> CREATE TABLE a (id int) ENGINE=InnoDB;
session2> START TRANSACTION WITH CONSISTENT SNAPSHOT;
session1> ALTER TABLE a ADD COLUMN name varchar(32);
session2> SELECT * FROM a;
ERROR 1412 (HY000): Table definition has changed, please retry transaction

p.s. 如果③和④调换顺序，则ALTER TABLE无法成功，则会等待MDL。

复现二：

① session1> START TRANSACTION WITH CONSISTENT SNAPSHOT;
② session2> CREATE TABLE b (id int) ENGINE=InnoDB;
③ session1> SELECT * FROM b;
ERROR 1412 (HY000): Table definition has changed, please retry transaction

6、备份MERGE存储引擎或者MyISAM损坏

mysqldump: Couldnt execute show create table $tb_name: Unable to open underlying table which is differently defined or of non-MyISAM type or doesnt exist (1168)

原因：出现在表引擎为MERGE时，备份到该表时，发现该表定义存在问题。可能merge的表不存在，或者该表合并的基表包含非MyISAM引擎的表。

处理思路：删除或者重建该MERGE表。

复现一（merge表中定义包含了非MyISAM表）：

CREATE TABLE t1(id int) ENGINE=InnoDB;
CREATE TABLE t2(id int) ENGINE=MyISAM;
CREATE TABLE merge_t(id int)ENGINE=MERGE UNION=(t1, t2); 
SELECT * FROM merge_t;
ERROR 1168 (HY000): Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist

复现二（表不存在）：

CREATE TABLE t1(id int) ENGINE=InnoDB;
CREATE TABLE t2(id int) ENGINE=MyISAM;
CREATE TABLE merge_t(id int)ENGINE=MERGE UNION=(t1, t2); 
SELECT * FROM merge_t;
ERROR 1168 (HY000): Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist

附录：

通过check table merge_t可以检查是哪张表有问题，如此处是t1：

[15:20:12] root@localhost [test]> check table merge_t\G
*************************** 1. row ***************************
   Table: test.merge_t
      Op: check
 Msg_type: Error
 Msg_text: Table 'test.t1' is differently defined or of non-MyISAM type or doesn't exist
 *************************** 2. row ***************************
   Table: test.merge_t
      Op: check
       Msg_type: Error
       Msg_text: Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist
  *************************** 3. row ***************************
      Table: test.merge_t
      Op: check
      Msg_type: error
     Msg_text: Corrupt
 3 rows in set (0.00 sec)

通过cat表MGR定义结构文件可以检查MERGE表的基表：

[root@host test]# pwd
/data/mysql-data/mysql57/data/test
[root@host test]# cat merge_t.MRG 
t1
t2

mysqldump: Couldnt execute show create table tb_name: Table ./db_name/tb_name is marked as crashed and last (automatic?) repair failed (144) OR mysqldump: Couldnt execute show create table $tb_name: Table ./db_name/tb_name is marked as crashed and should be repaired (145) ORmysqldump: Error 1194: Table tb_name is marked as crashed and should be repaired when dumping table tb_name at row: xxxxx

原因：mysqldump在拉取表定义时报错，表损坏。

处理思路：该损坏发生在非事务表如MyISAM，通过mysqlcheck或者repair table修复即可。

7、数据字典不存在或损坏

mysqldump: Couldnt execute show events: Cannot proceed because system tables used by Event Scheduler were found damaged at server start (1577)

原因：字典表不正确，极大可能是导入了其他版本的mysql schema盖掉了字典表。

处理思路：尝试mysql_upgrade来修复，或找到对应版本的mysql_system_tables_fix.sql来导入。可能有的情况，需要在upgrade操作之后重启实例。

8、tmpdir空间满

mysqldump: Error: Got error 28 from storage engine when trying to dump tablespaces OR mysqldump: Couldnt execute show fields from $tb_name: Got error 28 from storage engine (1030)

原因：@@tmpdir满。

处理思路：清除@@tmpdir，可以通过SELECT @@tmpdir;检查具体目录。

9、执行mysqlump期间mysqld被关闭

mysqldump: Lost connection to MySQL server during query (2013) OR ERROR 2002 (HY000): Can't connect to local MySQL server through socket '@@socket' (111)

原因：mysqldump执行过程中mysqld被关闭。

处理思路：检查mysqld被关闭的原因，一般常见原因是发生OOM。

10.mysqldump执行用户缺少权限

mysqldump: Couldn't execute 'SHOW SLAVE STATUS': Access denied; you need (at least one of) the SUPER, REPLICATION CLIENT privilege(s) for this operation (1227) OR mysqldump: Couldn't execute 'STOP SLAVE SQL_THREAD': Access denied for user 'dump'@'localhost' (using password: YES) (1045)

原因：mysqldump加了--dump-slave参数，缺少SUPER或REPLICATION CLIENT来执行SHOW SLAVE STATUS。或缺少SUPER权限使用STOP SLAVE SQL_THREAD。

处理思路：检查使用mysqldump的用户权限。

结尾

月黑风高，漆黑的夜晚，城市里的人们早已入梦，路边两个撸串的年轻男子。

正把酒言欢，酒过三巡，突然两位年轻男子拥抱痛哭。

此时的吵闹声与这个城市的宁静格格不入。

为何俩男子会情绪崩溃？

为何俩男子会相拥？

难道是...

且听下回：神谕为何深夜痛哭~

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