DROP TABLE 恢复【一】

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。

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> 

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> 

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。

[root@mysql-server- 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:
inode number:
protection:                          (regular file)
number of hard links:
user ID of owner:
group ID of owner:
device ID (if special file):
blocksize for filesystem I/O:
number of blocks allocated:
time of last access:             Sun Aug   ::
time of last modification:       Sun Aug   ::
time of last status change:      Sun Aug   ::
total size, in bytes:              (26.000 MiB)

Size to process:                   (26.000 MiB)
All workers finished in  sec
[root@mysql-server- undrop-for-innodb]# 

使用stream_parser将把数据从page保存到pages-ibdata1

[root@mysql-server- FIL_PAGE_INDEX]# pwd
/root/undrop-for-innodb/pages-ibdata1/FIL_PAGE_INDEX
[root@mysql-server- FIL_PAGE_INDEX]# ll
total
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
。。。。。。。。。。。。。。。。。。。。。。。。。
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page
-rw-r--r--  root root    Aug   : .page

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。

[root@mysql-server- undrop-for-innodb]# ./c_parser -4Df pages-ibdata1/FIL_PAGE_INDEX/.page -t dictionary/SYS_TABLES.sql | grep sakila/actor
    45000002B902C8  SYS_TABLES      "sakila/actor"                                    ""
    45000002B902C8  SYS_TABLES      "sakila/actor"                                    ""
SET FOREIGN_KEY_CHECKS=;
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- undrop-for-innodb]# 

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。

[root@mysql-server- undrop-for-innodb]# ./c_parser -4Df pages-ibdata1/FIL_PAGE_INDEX/.page -t dictionary/SYS_INDEXES.sql | grep
    45000002B90145  SYS_INDEXES                 "PRIMARY"
    45000002B901B7  SYS_INDEXES                 "idx\_actor\_last\_name"
    45000002B90145  SYS_INDEXES                 "PRIMARY"
    45000002B901B7  SYS_INDEXES                 "idx\_actor\_last\_name"
    45000002B90145  SYS_INDEXES                 "PRIMARY"
    45000002B901B7  SYS_INDEXES                 "idx\_actor\_last\_name"
SET FOREIGN_KEY_CHECKS=;
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- undrop-for-innodb]# 

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。

[root@mysql-server- undrop-for-innodb]# ./c_parser -6f pages-ibdata1/FIL_PAGE_INDEX/.page -t sakila/actor.sql |  head -
-- Page id: , Format: COMPACT, Records list: Valid, Expected records: ( )
00000000032C    AD000001750110  actor          "PENELOPE"      "GUINESS"       "2006-02-15 04:34:33"
00000000032C    AD00000175011A  actor          "NICK"  "WAHLBERG"      "2006-02-15 04:34:33"
00000000032C    AD000001750124  actor          "ED"    "CHASE" "2006-02-15 04:34:33"
00000000032C    AD00000175012E  actor          "JENNIFER"      "DAVIS" "2006-02-15 04:34:33"
00000000032C    AD000001750138  actor          "JOHNNY"        "LOLLOBRIGIDA"  "2006-02-15 04:34:33"
00000000032C    AD000001750142  actor          "BETTE" "NICHOLSON"     "2006-02-15 04:34:33"
00000000032C    AD00000175014C  actor          "GRACE" "MOSTEL"        "2006-02-15 04:34:33"
00000000032C    AD000001750156  actor          "MATTHEW"       "JOHANSSON"     "2006-02-15 04:34:33"
00000000032C    AD000001750160  actor          "JOE"   "SWANK" "2006-02-15 04:34:33"
[root@mysql-server- undrop-for-innodb]# 

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- undrop-for-innodb]#  mkdir -p dumps/default
[root@mysql-server- undrop-for-innodb]# 

[root@mysql-server- undrop-for-innodb]# ./c_parser -6f pages-ibdata1/FIL_PAGE_INDEX/.page -t sakila/actor.sql > dumps/default/actor > dumps/default/actor_load.sql
[root@mysql-server- undrop-for-innodb]# 

我们看看一个文件，其实是命令加载表而已

[root@mysql-server- undrop-for-innodb]# cat dumps/default/actor_load.sql
SET FOREIGN_KEY_CHECKS=;
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- 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

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> 

现在我们导入数据，恢复actor表

[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> 

检查恢复的数据

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> 

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/