当DROP TABLE指令敲下的时候，你很爽，你有考虑过后果么？如果该表真的没用，你DROP到无所谓，如果还有用的，这时你肯定吓惨了吧，如果你有备份，那么恭喜你，逃过一劫，如果没有备份呢？这时就该绝望了？NO! 如果你的表是innodb表，那么还有希望挽救，如果是myisam表，那么真的没救了。前面文章介绍了 Recover InnoDB dictionary，这是恢复数据的前提。恢复innodb字典信息使用的是TwinDB recovery toolkit，我们恢复数据也是使用该工具。下面的案例是基于innodb_file_per_table=OFF的前提下，即使用共享表空间，所有的信息都保存在ibdata1中。使用独立表空间DROP TABLE后数据恢复将在后面的文章介绍。
错误的操作--删除表
用到的示例数据库还是sakila，关于下载地址前面的文章有地址。将模拟把sakila库中的actor表删除后进行恢复。
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root@localhost : sakila 21:34:11> SELECT * FROM actor LIMIT 10;
+----------+------------+--------------+---------------------+
| actor_id | first_name | last_name | last_update |
+----------+------------+--------------+---------------------+
| 1 | PENELOPE | GUINESS | 2006-02-15 04:34:33 |
| 2 | NICK | WAHLBERG | 2006-02-15 04:34:33 |
| 3 | ED | CHASE | 2006-02-15 04:34:33 |
| 4 | JENNIFER | DAVIS | 2006-02-15 04:34:33 |
| 5 | JOHNNY | LOLLOBRIGIDA | 2006-02-15 04:34:33 |
| 6 | BETTE | NICHOLSON | 2006-02-15 04:34:33 |
| 7 | GRACE | MOSTEL | 2006-02-15 04:34:33 |
| 8 | MATTHEW | JOHANSSON | 2006-02-15 04:34:33 |
| 9 | JOE | SWANK | 2006-02-15 04:34:33 |
| 10 | CHRISTIAN | GABLE | 2006-02-15 04:34:33 |
+----------+------------+--------------+---------------------+
10 rows in set (0.01 sec)
root@localhost : sakila 21:34:25>
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root@localhost : sakila 21:34:25> CHECKSUM TABLE actor;
+--------------+------------+
| Table | Checksum |
+--------------+------------+
| sakila.actor | 2472295518 |
+--------------+------------+
1 row in set (0.07 sec)
root@localhost : sakila 21:35:30> SET foreign_key_checks=OFF;
Query OK, 0 rows affected (0.00 sec)
root@localhost : sakila 21:35:46> DROP TABLE actor;
Query OK, 0 rows affected (0.07 sec)
root@localhost : sakila 21:35:57>
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从ibdata1恢复数据
现在actor表已经删除，但表中的信息仍然存与ibdata1中。该数据保持不变，直到InnoDB的重用空闲的页。我们需要尽快停止mysqld进程。
对于恢复，我们将使用TwinDB恢复工具包。看看我前面的文章Recover InnoDB dictionary。
解析innodb表空间（ibdata1）
InnoDB将所有数据存储在B +树索引。 一个表有只有一个聚集索引,所有字段存储在这里。 如果表有辅助索引，由index_id标识每个索引。
如果我们要恢复一个表，我们必须找到属于特定index_id的所有页面。
stream_parser读取InnoDB表和排序按类型和每个index_id的InnoDB的页面。
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[root@mysql-server-01 undrop-for-innodb]# ./stream_parser -f /data/mysql/user_3306/data/ibdata1
Opening file: /data/mysql/user_3306/data/ibdata1
File information:
ID of device containing file: 2055
inode number: 77760163
protection: 100660 (regular file)
number of hard links: 1
user ID of owner: 498
group ID of owner: 500
device ID (if special file): 0
blocksize for filesystem I/O: 4096
number of blocks allocated: 53248
time of last access: 1407057329 Sun Aug 3 17:15:29 2014
time of last modification: 1407072967 Sun Aug 3 21:36:07 2014
time of last status change: 1407072967 Sun Aug 3 21:36:07 2014
total size, in bytes: 27262976 (26.000 MiB)
Size to process: 27262976 (26.000 MiB)
All workers finished in 0 sec
[root@mysql-server-01 undrop-for-innodb]#
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使用stream_parser将把数据从page保存到pages-ibdata1
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[root@mysql-server-01 FIL_PAGE_INDEX]# pwd
/root/undrop-for-innodb/pages-ibdata1/FIL_PAGE_INDEX
[root@mysql-server-01 FIL_PAGE_INDEX]# ll
total 6976
-rw-r--r-- 1 root root 32768 Aug 3 21:59 0000000000000001.page
-rw-r--r-- 1 root root 49152 Aug 3 21:59 0000000000000002.page
-rw-r--r-- 1 root root 49152 Aug 3 21:59 0000000000000003.page
-rw-r--r-- 1 root root 49152 Aug 3 21:59 0000000000000004.page
-rw-r--r-- 1 root root 32768 Aug 3 21:59 0000000000000005.page
。。。。。。。。。。。。。。。。。。。。。。。。。
-rw-r--r-- 1 root root 16384 Aug 3 21:59 0000000000000011.page
-rw-r--r-- 1 root root 16384 Aug 3 21:59 0000000000000012.page
-rw-r--r-- 1 root root 16384 Aug 3 21:59 0000000000000013.page
-rw-r--r-- 1 root root 16384 Aug 3 21:59 0000000000000053.page
-rw-r--r-- 1 root root 16384 Aug 3 21:59 0000000000000054.page
-rw-r--r-- 1 root root 16384 Aug 3 21:59 0000000000000055.page
-rw-r--r-- 1 root root 16384 Aug 3 21:59 18446744069414584320.page
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现在InnoDB表空间的每个index_id被保存在一个单独的文件。我们可以用c_parser工具从page提取记录。但是，我们需要知道哪个index_id对应表Sakila/actor。这些信息，我们可以从字典中获取：SYS_TABLES和SYS_INDEXES。
SYS_TABLES始终存储在文件index_id为1的page，ibdata1/FIL_PAGE_INDEX/0000000000000001.page 这让我们找到Sakila/actor表的标识符。如果MySQL有足够的时间来刷新到磁盘的变化再加入D选项，意思是“寻找被删除的记录“，innodb字典信息永远是冗余格式，所以我们需要指定选项-4。
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[root@mysql-server-01 undrop-for-innodb]# ./c_parser -4Df pages-ibdata1/FIL_PAGE_INDEX/0000000000000001.page -t dictionary/SYS_TABLES.sql | grep sakila/actor
000000000344 45000002B902C8 SYS_TABLES "sakila/actor" 13 4 1 0 0 "" 0
000000000344 45000002B902C8 SYS_TABLES "sakila/actor" 13 4 1 0 0 "" 0
SET FOREIGN_KEY_CHECKS=0;
LOAD DATA LOCAL INFILE '/root/undrop-for-innodb/dumps/default/SYS_TABLES' REPLACE INTO TABLE `SYS_TABLES` FIELDS TERMINATED BY '\t' OPTIONALLY ENCLOSED BY '"' LINES STARTING BY 'SYS_TABLES\t' (`NAME`, `ID`, `N_COLS`, `TYPE`, `MIX_ID`, `MIX_LEN`, `CLUSTER_NAME`, `SPACE`);
[root@mysql-server-01 undrop-for-innodb]#
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注意表名之后的数13。这是表标识符。这和前面的文章不谋而合，Recover InnoDB dictionary
接下来的事情，需要做的是找到actor表的的主键ID。为此，我们将从SYS_INDEXES文件0000000000000003.page获取记录（该表将包含有关index_id和表标识符信息）。 SYS_INDEXES的结构需要通过-t选项解析。
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[root@mysql-server-01 undrop-for-innodb]# ./c_parser -4Df pages-ibdata1/FIL_PAGE_INDEX/0000000000000003.page -t dictionary/SYS_INDEXES.sql | grep 13
000000000344 45000002B90145 SYS_INDEXES 13 15 "PRIMARY" 1 3 0 4294967295
000000000344 45000002B901B7 SYS_INDEXES 13 16 "idx\_actor\_last\_name" 1 0 0 4294967295
000000000344 45000002B90145 SYS_INDEXES 13 15 "PRIMARY" 1 3 0 4294967295
000000000344 45000002B901B7 SYS_INDEXES 13 16 "idx\_actor\_last\_name" 1 0 0 4294967295
000000000344 45000002B90145 SYS_INDEXES 13 15 "PRIMARY" 1 3 0 4294967295
000000000344 45000002B901B7 SYS_INDEXES 13 16 "idx\_actor\_last\_name" 1 0 0 4294967295
SET FOREIGN_KEY_CHECKS=0;
LOAD DATA LOCAL INFILE '/root/undrop-for-innodb/dumps/default/SYS_INDEXES' REPLACE INTO TABLE `SYS_INDEXES` FIELDS TERMINATED BY '\t' OPTIONALLY ENCLOSED BY '"' LINES STARTING BY 'SYS_INDEXES\t' (`TABLE_ID`, `ID`, `NAME`, `N_FIELDS`, `TYPE`, `SPACE`, `PAGE_NO`);
[root@mysql-server-01 undrop-for-innodb]#
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我们可以从输出看到，PRIMARY index_id标示符是15。因此，我们的数据将从0000000000000015.page寻找。
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[root@mysql-server-01 undrop-for-innodb]# ./c_parser -6f pages-ibdata1/FIL_PAGE_INDEX/0000000000000015.page -t sakila/actor.sql | head -10
-- Page id: 307, Format: COMPACT, Records list: Valid, Expected records: (200 200)
00000000032C AD000001750110 actor 1 "PENELOPE" "GUINESS" "2006-02-15 04:34:33"
00000000032C AD00000175011A actor 2 "NICK" "WAHLBERG" "2006-02-15 04:34:33"
00000000032C AD000001750124 actor 3 "ED" "CHASE" "2006-02-15 04:34:33"
00000000032C AD00000175012E actor 4 "JENNIFER" "DAVIS" "2006-02-15 04:34:33"
00000000032C AD000001750138 actor 5 "JOHNNY" "LOLLOBRIGIDA" "2006-02-15 04:34:33"
00000000032C AD000001750142 actor 6 "BETTE" "NICHOLSON" "2006-02-15 04:34:33"
00000000032C AD00000175014C actor 7 "GRACE" "MOSTEL" "2006-02-15 04:34:33"
00000000032C AD000001750156 actor 8 "MATTHEW" "JOHANSSON" "2006-02-15 04:34:33"
00000000032C AD000001750160 actor 9 "JOE" "SWANK" "2006-02-15 04:34:33"
[root@mysql-server-01 undrop-for-innodb]#
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看见上面的输出，是不是觉得希望来了？哈哈
上面的结果正是我们想要的，我们现在把数据存贮在文件中，然后倒入，创建dump/default目录存储数据。
[root@mysql-server-01 undrop-for-innodb]# mkdir -p dumps/default
[root@mysql-server-01 undrop-for-innodb]#
[root@mysql-server-01 undrop-for-innodb]# ./c_parser -6f pages-ibdata1/FIL_PAGE_INDEX/0000000000000015.page -t sakila/actor.sql > dumps/default/actor 2> dumps/default/actor_load.sql
[root@mysql-server-01 undrop-for-innodb]#
我们看看一个文件，其实是命令加载表而已
[root@mysql-server-01 undrop-for-innodb]# cat dumps/default/actor_load.sql
SET FOREIGN_KEY_CHECKS=0;
LOAD DATA LOCAL INFILE '/root/undrop-for-innodb/dumps/default/actor' REPLACE INTO TABLE `actor` FIELDS TERMINATED BY '\t' OPTIONALLY ENCLOSED BY '"' LINES STARTING BY 'actor\t' (`actor_id`, `first_name`, `last_name`, `last_update`);
[root@mysql-server-01 undrop-for-innodb]#
将数据load回数据库中
现在将数据恢复到数据库中。但是，在导入数据以前，我们需要创建表actor（前提我们要有表结构备份，如果没有只有使用另外的工具找到表结构Percona Data Recovery Tool）看来还是需要两个工具结合使用啊。
root@localhost : sakila 23:03:50> source sakila/actor.sql
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root@localhost : sakila 23:03:50> show create table actor\G
*************************** 1. row ***************************
Table: actor
Create Table: CREATE TABLE `actor` (
`actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`first_name` varchar(45) NOT NULL,
`last_name` varchar(45) NOT NULL,
`last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`actor_id`),
KEY `idx_actor_last_name` (`last_name`)
) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
root@localhost : sakila 23:04:36>
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现在我们导入数据，恢复actor表
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[root@mysql-server-01 undrop-for-innodb]# mysql -uroot -p123456 -S /data/mysql/user_3306/mysql.sock --local-infile
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 18
Server version: 5.5.37-log MySQL Community Server (GPL)
Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
root@localhost : (none) 23:17:16> use sakila
Database changed
root@localhost : sakila 23:17:19> source dumps/default/actor_load.sql;
Query OK, 0 rows affected (0.00 sec)
Query OK, 600 rows affected (0.08 sec)
Records: 400 Deleted: 200 Skipped: 0 Warnings: 0
root@localhost : sakila 23:17:22>
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检查恢复的数据
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root@localhost : sakila 23:19:00> SELECT COUNT(*) FROM actor;
+----------+
| COUNT(*) |
+----------+
| 200 |
+----------+
1 row in set (0.00 sec)
root@localhost : sakila 23:19:34> SELECT * FROM actor LIMIT 10;
+----------+------------+--------------+---------------------+
| actor_id | first_name | last_name | last_update |
+----------+------------+--------------+---------------------+
| 1 | PENELOPE | GUINESS | 2006-02-15 04:34:33 |
| 2 | NICK | WAHLBERG | 2006-02-15 04:34:33 |
| 3 | ED | CHASE | 2006-02-15 04:34:33 |
| 4 | JENNIFER | DAVIS | 2006-02-15 04:34:33 |
| 5 | JOHNNY | LOLLOBRIGIDA | 2006-02-15 04:34:33 |
| 6 | BETTE | NICHOLSON | 2006-02-15 04:34:33 |
| 7 | GRACE | MOSTEL | 2006-02-15 04:34:33 |
| 8 | MATTHEW | JOHANSSON | 2006-02-15 04:34:33 |
| 9 | JOE | SWANK | 2006-02-15 04:34:33 |
| 10 | CHRISTIAN | GABLE | 2006-02-15 04:34:33 |
+----------+------------+--------------+---------------------+
10 rows in set (0.00 sec)
root@localhost : sakila 23:19:37> CHECKSUM TABLE actor;
+--------------+------------+
| Table | Checksum |
+--------------+------------+
| sakila.actor | 2472295518 |
+--------------+------------+
1 row in set (0.00 sec)
root@localhost : sakila 23:19:40>
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可以发现和drop table之前完全一致。到这里数据就恢复完成啦。希望小伙伴们永远不要使用到改工具。
参考资料
https://twindb.com/recover-innodb-table-after-drop-table-innodb/
作者：Atlas
出处：Atlas的博客 http://www.cnblogs.com/gomysql
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