运行着Innodb 引擎的MySQL 在遇到硬件故障,内核bug 或者是突然断电,MySQL本身的bug,可能会造成Innodb表空间的损坏,提示的信息大致如下:
InnoDB: Database page corruption on disk or a failed InnoDB: file read of page 7. InnoDB: You may have to recover from a backup. 080703 23:46:16 InnoDB: Page dump in ascii and hex (16384 bytes): … A LOT OF HEX AND BINARY DATA… 080703 23:46:16 InnoDB: Page checksum 587461377, prior-to-4.0.14-form checksum 772331632 InnoDB: stored checksum 2287785129, prior-to-4.0.14-form stored checksum 772331632 InnoDB: Page lsn 24 1487506025, low 4 bytes of lsn at page end 1487506025 InnoDB: Page number (if stored to page already) 7, InnoDB: space id (if created with >= MySQL-4.1.1 and stored already) 6353 InnoDB: Page may be an index page where index id is 0 25556 InnoDB: (index “PRIMARY” of table “test”.”test”) InnoDB: Database page corruption on disk or a failed
提示出现断言错误(assertion failure);
对于损坏的表,大致可分为三种情况,Data corrupted In Secondary Index, Data corrupted In clustered key,Data corrupted In table dictionary,恢复难度依次增加;
下面我们来做一个简单恢复实验,我手动编辑test.ibd 文件,只修改一小部分,此时,我手动check 一下:
mysql> check table test; ERROR 2013 (HY000): Lost connection to MySQL server during query mysql> check table test; +-----------+-------+----------+----------+ | Table | Op | Msg_type | Msg_text | +-----------+-------+----------+----------+ | test.test | check | status | OK | +-----------+-------+----------+----------+ 1 row in set (0.69 sec)
第一次运行的时候,Innodb发现checksum error并出现crash的情况(运行check 的时候同样会发生crash),第二次运行的时候我设置了 innodb_force_recovery=1,但是check 的结果却是ok,对于check功能还是不要太过相信啊,
在Innodb_force_recovery=1 的情况下,我们可以建一张引擎为MyISAM同样表结构的表,对新表导入数据,然后去掉force recovery选项,重启MyISAM,并将引擎转换为INNODB,:
mysql> CREATE TABLE `test2` ( -> `c` char(255) DEFAULT NULL, -> `id` int(10) unsigned NOT NULL AUTO_INCREMENT, -> PRIMARY KEY (`id`) -> ) ENGINE=MYISAM; Query OK, 0 rows affected (0.03 sec) mysql> insert into test2 select * from test; Query OK, 229376 rows affected (0.91 sec) Records: 229376 Duplicates: 0 Warnings: 0
以上的操作确实有点简单,下面我们尝试把test.ibd 的page header部分全部擦除,这次甚至在innodb_force_recovery=1 的情况下,运行check table 同样会出现断言的错误(Assertion failure):
080704 0:22:53 InnoDB: Assertion failure in thread 1158060352 in file btr/btr0btr.c line 3235 InnoDB: Failing assertion: page_get_n_recs(page) > 0 || (level == 0 && page_get_page_no(page) == dict_index_get_page(index)) InnoDB: We intentionally generate a memory trap. InnoDB: Submit a detailed bug report to http://bugs.mysql.com. InnoDB: If you get repeated assertion failures or crashes, even
这个时候,提高innodb_force_recovery 参数值,也还是可能出现下面的情况:
mysql> insert into test2 select * from test; ERROR 2013 (HY000): Lost connection to MySQL server during query
对于上面这个语句,我们可能认为 当扫描table时第一次遇到corrupted的row时,会报错,并把已扫描的row存储在MyISAM(非事务型存储引擎)中,但实践是test2最终是没有记录的,原因是:there is some buffering taking place and as MySQL crashes it does not store all data it could recover to MyISAM table;(对这个理解还不是很懂)
对于这种情况,只能加上limit,一部分一部分的导入:
mysql> insert ignore into test2 select * from test limit 10; Query OK, 10 rows affected (0.00 sec) Records: 10 Duplicates: 0 Warnings: 0 mysql> insert ignore into test2 select * from test limit 20; Query OK, 10 rows affected (0.00 sec) Records: 20 Duplicates: 10 Warnings: 0 mysql> insert ignore into test2 select * from test limit 100; Query OK, 80 rows affected (0.00 sec) Records: 100 Duplicates: 20 Warnings: 0 mysql> insert ignore into test2 select * from test limit 200; Query OK, 100 rows affected (1.47 sec) Records: 200 Duplicates: 100 Warnings: 0 mysql> insert ignore into test2 select * from test limit 300; ERROR 2013 (HY000): Lost connection to MySQL server during query
以上我们可以得出,损坏的row就在200行-300行之间,下面我们可以使用二分查找,在次缩小查找范围,
mysql> select max(id) from test2; +---------+ | max(id) | +---------+ | 220 | +---------+ 1 row in set (0.00 sec) mysql> insert ignore into test2 select * from test where id>250; ERROR 2013 (HY000): Lost connection to MySQL server during query mysql> insert ignore into test2 select * from test where id>300; Query OK, 573140 rows affected (7.79 sec) Records: 573140 Duplicates: 0 Warnings: 0
当跳过80行的时候,才insert成功;如果是 directory page 损坏,我们可能需要跳过更多page,如果是损坏的 higher level btree,可能会跳过更多,,,
在一些个别场景中像Data dictionary 或者root page 损坏,上面的方式可能不会奏效,此时可以尝试一把 innodb recovery toolkit 。。。