如何在删除ibdata1和ib_logfile的情况下恢复MySQL数据库
昨天，有个朋友对公司内部使用的一个MySQL实例开启binlog，但是在启动的过程中失败了（他也没提，为何会失败），在启动失败后，他删除了ibdata1和ib_logfile，后来，能正常启动了，但所有的表通过show tables能看到，但是select的过程中却报“Table doesn't exist”。
于是，建议他试试可传输表空间。
同时，自己也测试了下，确实可行。
测试版本 MySQL 5.6.32 社区版
恢复的基本步骤
1. 将原来的数据文件COPY到其它目录下。
2. 创建同名表，表结构必须保持一致。
3. 导出表空间
mysql> ALTER TABLE t DISCARD TABLESPACE;
4. 将原来的数据文件COPY回来
5. 导入表空间
mysql> ALTER TABLE t IMPORT TABLESPACE
下面的演示会略为复杂，主要是还原整个场景，并针对上述步骤中的2,4做了一个测试。
首先，创建测试数据
在这里创建两张表。之所以创建两张相同的表是为了方便后续的测试。
mysql> create table t1(id int,hiredate datetime); Query OK, 0 rows affected (0.14 sec) mysql> create table t2(id int,hiredate datetime); Query OK, 0 rows affected (0.01 sec) mysql> insert into t1 values(1,now()); Query OK, 1 row affected (0.06 sec) mysql> insert into t1 values(2,now()); Query OK, 1 row affected (0.00 sec) mysql> insert into t2 values(1,now()); Query OK, 1 row affected (0.00 sec) mysql> insert into t2 values(2,now()); Query OK, 1 row affected (0.00 sec)
关闭数据库
# /usr/test/mysql-5.6.32-linux-glibc2.5-x86_64/bin/mysqladmin shutdown -uroot -p123456 -h127.0.0.1 -P3310
删除ibdata1，ib_logfile0和ib_logfile1
[root@localhost data]# cd /data/ [root@localhost data]# ls auto.cnf ib_logfile0 localhost.localdomain.err mysql_upgrade_info test ibdata1 ib_logfile1 mysql performance_schema [root@localhost data]# rm -rf ibdata1 [root@localhost data]# rm -rf ib_logfile*[root@localhost data]# ls auto.cnf localhost.localdomain.err mysql mysql_upgrade_info performance_schema test
重新启动数据库
# /usr/test/mysql-5.6.32-linux-glibc2.5-x86_64/bin/mysqld --defaults-file=/usr/test/mysql-5.6.32-linux-glibc2.5-x86_64/my.cnf &
并没有报错
启动过程中的日志信息如下：
# 2016-08-18 11:13:18 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details). 2016-08-18 11:13:18 0 [Note] /usr/test/mysql-5.6.32-linux-glibc2.5-x86_64/bin/mysqld (mysqld 5.6.32) starting as process 3948 ... 2016-08-18 11:13:18 3948 [Note] Plugin 'FEDERATED' is disabled. 2016-08-18 11:13:18 3948 [Note] InnoDB: Using atomics to ref count buffer pool pages 2016-08-18 11:13:18 3948 [Note] InnoDB: The InnoDB memory heap is disabled 2016-08-18 11:13:18 3948 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins 2016-08-18 11:13:18 3948 [Note] InnoDB: Memory barrier is not used 2016-08-18 11:13:18 3948 [Note] InnoDB: Compressed tables use zlib 1.2.3 2016-08-18 11:13:18 3948 [Note] InnoDB: Using Linux native AIO 2016-08-18 11:13:18 3948 [Note] InnoDB: Using CPU crc32 instructions 2016-08-18 11:13:18 3948 [Note] InnoDB: Initializing buffer pool, size = 128.0M 2016-08-18 11:13:19 3948 [Note] InnoDB: Completed initialization of buffer pool 2016-08-18 11:13:19 3948 [Note] InnoDB: The first specified data file ./ibdata1 did not exist: a new database to be created! 2016-08-18 11:13:19 3948 [Note] InnoDB: Setting file ./ibdata1 size to 12 MB 2016-08-18 11:13:19 3948 [Note] InnoDB: Database physically writes the file full: wait... 2016-08-18 11:13:19 3948 [Note] InnoDB: Setting log file ./ib_logfile101 size to 48 MB 2016-08-18 11:13:21 3948 [Note] InnoDB: Setting log file ./ib_logfile1 size to 48 MB 2016-08-18 11:13:22 3948 [Note] InnoDB: Renaming log file ./ib_logfile101 to ./ib_logfile0 2016-08-18 11:13:22 3948 [Warning] InnoDB: New log files created, LSN=45781 2016-08-18 11:13:22 3948 [Note] InnoDB: Doublewrite buffer not found: creating new 2016-08-18 11:13:22 3948 [Note] InnoDB: Doublewrite buffer created 2016-08-18 11:13:22 3948 [Note] InnoDB: 128 rollback segment(s) are active. 2016-08-18 11:13:22 3948 [Warning] InnoDB: Creating foreign key constraint system tables. 2016-08-18 11:13:22 3948 [Note] InnoDB: Foreign key constraint system tables created 2016-08-18 11:13:22 3948 [Note] InnoDB: Creating tablespace and datafile system tables. 2016-08-18 11:13:22 3948 [Note] InnoDB: Tablespace and datafile system tables created. 2016-08-18 11:13:22 3948 [Note] InnoDB: Waiting for purge to start 2016-08-18 11:13:22 3948 [Note] InnoDB: 5.6.32 started; log sequence number 0 2016-08-18 11:13:22 3948 [Note] Server hostname (bind-address): '*'; port: 3310 2016-08-18 11:13:23 3948 [Note] IPv6 is available. 2016-08-18 11:13:23 3948 [Note] - '::' resolves to '::'; 2016-08-18 11:13:23 3948 [Note] Server socket created on IP: '::'. 2016-08-18 11:13:23 3948 [Note] Event Scheduler: Loaded 0 events 2016-08-18 11:13:23 3948 [Note] /usr/test/mysql-5.6.32-linux-glibc2.5-x86_64/bin/mysqld: ready for connections. Version: '5.6.32' socket: '/data/mysql.sock' port: 3310 MySQL Community Server (GPL)
可见，在启动的过程中，MySQL会重建ibdata1和redo log。
登录mysql客户端，看之前创建的t1，t2是否能访问
# /usr/test/mysql-5.6.32-linux-glibc2.5-x86_64/bin/mysql -h127.0.0.1 -p123456 -uroot -P3310
mysql> use test Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> show tables; +----------------+ | Tables_in_test | +----------------+ | t1 | | t2 | +----------------+ 2 rows in set (0.00 sec) mysql> select * from t1; ERROR 1146 (42S02): Table 'test.t1' doesn't exist
通过show tables能查看有t1表存在，但表中的具体内容则无法查看
同时，错误日志中输出以下信息
2016-08-18 11:15:13 3948 [Warning] InnoDB: Cannot open table test/t1 from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.
将数据目录下的test目录中的t1，t2表的数据文件和表定义文件COPY到其它地方
[root@localhost test]# cd /data/test/ [root@localhost test]# ll total 216 -rw-rw---- 1 mysql mysql 8594 Aug 18 11:06 t1.frm -rw-rw---- 1 mysql mysql 98304 Aug 18 11:07 t1.ibd -rw-rw---- 1 mysql mysql 8594 Aug 18 11:06 t2.frm -rw-rw---- 1 mysql mysql 98304 Aug 18 11:07 t2.ibd [root@localhost test]# mv * /backup/ [root@localhost test]# ls [root@localhost test]# ll /backup/ total 216 -rw-rw---- 1 mysql mysql 8594 Aug 18 11:06 t1.frm -rw-rw---- 1 mysql mysql 98304 Aug 18 11:07 t1.ibd -rw-rw---- 1 mysql mysql 8594 Aug 18 11:06 t2.frm -rw-rw---- 1 mysql mysql 98304 Aug 18 11:07 t2.ibd
登录客户端，创建t1和t2表，注意表结构和之前的必须保持一致
细心的童鞋会发现，下面的创表语句和刚开始的创表语句并不一样，列名不一致，这个其实是为了后续的测试
mysql> show tables; Empty set (0.00 sec) mysql> create table t1(id_1 int,hiredate_1 datetime); ERROR 1146 (42S02): Table 'test.t1' doesn't exist
明明已经手动移除了，为什么创建表的时候还报这个错误呢？
接下来，可先执行个drop table操作
mysql> drop table t1; ERROR 1051 (42S02): Unknown table 'test.t1' mysql> create table t1(id_1 int,hiredate_1 datetime); Query OK, 0 rows affected (0.07 sec)
对于t2表，我们定义一个不同的表结构，看是否可行？
mysql> drop table t2; ERROR 1051 (42S02): Unknown table 'test.t2' mysql> create table t2(id_1 int); Query OK, 0 rows affected (0.01 sec)
导出表空间
mysql> ALTER TABLE t1 DISCARD TABLESPACE; Query OK, 0 rows affected (0.00 sec) mysql> ALTER TABLE t2 DISCARD TABLESPACE; Query OK, 0 rows affected (0.00 sec)
这个时候，数据目录下的test目录下，数据文件没有了，只剩下了表结构文件
[root@localhost test]# ls t1.frm t2.frm
导入表空间
首先对t1表进行测试
在这里，测试如下两种情况
1. 新的t1.frm+旧的t1.ibd
2. 旧的t1.frm+旧的t1.ibd
第一种情况
只是将t1表的数据文件COPY回来
[root@localhost test]# cp /backup/t1.ibd . [root@localhost test]# chown mysql.mysql t1.ibd
导入t1表的表空间
mysql> ALTER TABLE t1 IMPORT TABLESPACE; Query OK, 0 rows affected, 1 warning (0.21 sec) mysql> show warnings; +---------+------+-----------------------------------------------------------------------------------------------------------------------------------------+ | Level | Code | Message | +---------+------+-----------------------------------------------------------------------------------------------------------------------------------------+ | Warning | 1810 | InnoDB: IO Read error: (2, No such file or directory) Error opening './test/t2.cfg', will attempt to import without schema verification | +---------+------+-----------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
查看t1表是否能访问
mysql> select * from t1; +------+---------------------+ | id_1 | hiredate_1 | +------+---------------------+ | 1 | 2016-08-18 17:45:02 | | 2 | 2016-08-18 17:45:02 | +------+---------------------+ 2 rows in set (0.00 sec) mysql> flush table t1; Query OK, 0 rows affected (0.00 sec) mysql> select * from t1; +------+---------------------+ | id_1 | hiredate_1 | +------+---------------------+ | 1 | 2016-08-18 17:45:02 | | 2 | 2016-08-18 17:45:02 | +------+---------------------+ 2 rows in set (0.00 sec)
喔，确实能访问，注意观察，表的列名与新的创表语句保持一致。
在这里之所以使用flush table操作，是为了刷新内存中的表定义。
下面看看t1的第二种情况，旧的t1.frm+旧的t1.ibd
mysql> ALTER TABLE t1 DISCARD TABLESPACE; Query OK, 0 rows affected (0.00 sec)
[root@localhost test]# cp /backup/t1.frm . cp: overwrite `./t1.frm'? y [root@localhost test]# cp /backup/t1.ibd . [root@localhost test]# chown mysql.mysql t1.frm [root@localhost test]# chown mysql.mysql t1.ibd
mysql> ALTER TABLE t1 import TABLESPACE; Query OK, 0 rows affected, 1 warning (0.04 sec) mysql> select * from t1; +------+---------------------+ | id_1 | hiredate_1 | +------+---------------------+ | 1 | 2016-08-18 17:45:02 | | 2 | 2016-08-18 17:45:02 | +------+---------------------+ 2 rows in set (0.00 sec) mysql> flush table t1; Query OK, 0 rows affected (0.00 sec) mysql> select * from t1; +------+---------------------+ | id | hiredate | +------+---------------------+ | 1 | 2016-08-18 17:45:02 | | 2 | 2016-08-18 17:45:02 | +------+---------------------+ 2 rows in set (0.00 sec)
第一次查询的时候还是新的列名，对表进行flush后，就恢复到原来的列名了。
下面来看看t2表的导入情况
因为t2表的表结构发生了改变，在这里，也是测试如下两种情况
1. 新的t2.frm+旧的t2.ibd
2. 旧的t2.frm+旧的t2.ibd
首先，只是导入t2表的数据文件
[root@localhost test]# cp /backup/t2.ibd . [root@localhost test]# ll total 216 -rw-rw---- 1 mysql mysql 8594 Aug 18 17:55 t1.frm -rw-r----- 1 mysql mysql 98304 Aug 18 18:00 t1.ibd -rw-rw---- 1 mysql mysql 8556 Aug 18 17:52 t2.frm -rw-r----- 1 root root 98304 Aug 18 18:10 t2.ibd [root@localhost test]# chown mysql.mysql t2.ibd
导入t2表的表空间进行测试
mysql> ALTER TABLE t2 import TABLESPACE; Query OK, 0 rows affected, 1 warning (0.03 sec) mysql> select * from t2; +------+ | id_1 | +------+ | 1 | | 2 | +------+ 2 rows in set (0.00 sec) mysql> flush table t2; Query OK, 0 rows affected (0.00 sec) mysql> select * from t2; +------+ | id_1 | +------+ | 1 | | 2 | +------+ 2 rows in set (0.00 sec)
从结果可以看出，只能读出第一列。
下面测试第二种情况，旧的t2.frm和t2.ibd
mysql> ALTER TABLE t2 DISCARD TABLESPACE; Query OK, 0 rows affected (0.06 sec)
[root@localhost test]# rm -rf t2.frm [root@localhost test]# cp /backup/t2.frm . [root@localhost test]# cp /backup/t2.ibd . [root@localhost test]# chown mysql.mysql t2.frm [root@localhost test]# chown mysql.mysql t2.ibd
mysql> ALTER TABLE t2 import TABLESPACE; Query OK, 0 rows affected, 1 warning (0.09 sec) mysql> select * from t2; +------+ | id_1 | +------+ | 1 | | 2 | +------+ 2 rows in set (0.00 sec) mysql> flush table t2; Query OK, 0 rows affected (0.00 sec) mysql> select * from t2; ERROR 1146 (42S02): Table 'test.t2' doesn't exist
在重新刷新后，就出现错误了，个人感觉，这个和系统表空间中的数据字典信息有关。
实际上，后续还测试了一下，如果将hiredate的列定义为varchar，则无论是使用之前的frm文件还是之后的，在导入表空间，进行查询时，数据库直接挂掉。
mysql> create table t1(id int,hiredate varchar(10)); Query OK, 0 rows affected (0.05 sec) mysql> ALTER TABLE t1 DISCARD TABLESPACE; Query OK, 0 rows affected (0.00 sec) mysql> ALTER TABLE t1 import TABLESPACE; Query OK, 0 rows affected, 1 warning (0.03 sec) mysql> select * from t1; ERROR 2013 (HY000): Lost connection to MySQL server during query
结论
经过上面的一系列测试，可以看到
1. 使用可传输表空间，可以解决在删除ibdata1和ib_logfile的情况下恢复MySQL数据库，当然，本文测试的前提是数据库正常关闭下删除的ibdata1和ib_logfile。
2. 使用可传输表空间，建议新建表的表结构和原来的表结构完全一致，同时，在导入表空间前，只需COPY回原来的数据文件，即ibd。
事实上，在数据库正常关闭下删除ibdata1，会导致mysql库中的以下几张表无法访问
mysql> select table_name from information_schema.tables where table_schema='mysql' and engine='innodb'; +----------------------+ | table_name | +----------------------+ | innodb_index_stats | | innodb_table_stats | | slave_master_info | | slave_relay_log_info | | slave_worker_info | +----------------------+ 5 rows in set (0.00 sec) mysql> select * from mysql.innodb_index_stats; ERROR 1146 (42S02): Table 'mysql.innodb_index_stats' doesn't exist mysql> select * from mysql.innodb_table_stats; ERROR 1146 (42S02): Table 'mysql.innodb_table_stats' doesn't exist mysql> select * from mysql.slave_master_info; ERROR 1146 (42S02): Table 'mysql.slave_master_info' doesn't exist mysql> select * from mysql.slave_relay_log_info; ERROR 1146 (42S02): Table 'mysql.slave_relay_log_info' doesn't exist mysql> select * from mysql.slave_worker_info; ERROR 1146 (42S02): Table 'mysql.slave_worker_info' doesn't exist
同时，错误日志中报如下信息
2016-08-19 12:10:18 3041 [Warning] InnoDB: Cannot open table mysql/innodb_index_stats from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem. 2016-08-19 12:10:26 3041 [Warning] InnoDB: Cannot open table mysql/innodb_table_stats from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem. 2016-08-19 12:10:34 3041 [Warning] InnoDB: Cannot open table mysql/slave_master_info from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem. 2016-08-19 12:10:40 3041 [Warning] InnoDB: Cannot open table mysql/slave_relay_log_info from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem. 2016-08-19 12:10:46 3041 [Warning] InnoDB: Cannot open table mysql/slave_worker_info from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.
要解决这个问题，只能重建这些表。
参考
1. http://dev.mysql.com/doc/refman/5.6/en/tablespace-copying.html
2. http://dba.stackexchange.com/questions/48166/cannot-open-table-mysql-innodb-index-stats
