背景
最近一个朋友说，程序误删了一张表，但是没有备份。我一心想，这不是凉凉了。因为按照正常的情况，如果误删了表，在有备份的情况下，可以通过备份+binlog的方式找回数据。如果没有备份的话，想找回数据基本是没什么希望了。本着死马当活马医的态度，在网上google了一阵，发现了竟然还有undrop-for-innodb这一个工具。
undrop-for-innodb工具按照描述，是可以实现在无备份的情况下，通过扫描ibdata1文件和磁盘文件，来找回删除表的数据。话不多说，立马实验一下。
恢复步骤
使用undrop-for-innodb工具分两种情况，分别是innodb_file_per_table=OFF和innodb_file_per_table=ON两种情况。innodb_file_per_table参数描述了innodb存储引擎存储数据的方式。如果为OFF，则库表的所有数据都存放在ibdata*的共享表空间内，若为ON，则每个表会生成独立的文件来存储数据。
在如今的mysql版本中，innodb_file_per_table参数默认为ON，于是这里来重点讲一下innodb_file_per_table=ON的这种情况。
一：安装undrop-for-innodb工具。
# git clone https://github.com/twindb/undrop-for-innodb.git # yum install -y make gcc flex bison # cd undrop-for-innodb # make
安装完之后，会在undrop-for-innodb目录下生成stream_parser和c_parser文件。
二：模拟mysql表误删操作：
这里我有一个iceny.assets_host_auth，里面存放了一些我自己系统的用户信息，如下：
删除assets_host_auth表：
mysql> drop table assets_host_auth; Query OK, 0 rows affected (0.01 sec)
三，扫描磁盘页以及ibdata文件
# df -k Filesystem 1K-blocks Used Available Use% Mounted on /dev/mapper/centos-root 19703808 6701800 13002008 35% / devtmpfs 922464 0 922464 0% /dev tmpfs 933524 0 933524 0% /dev/shm tmpfs 933524 16952 916572 2% /run tmpfs 933524 0 933524 0% /sys/fs/cgroup /dev/sda1 201380 123252 78128 62% /boot tmpfs 186708 0 186708 0% /run/user/0 # ./stream_parser -f /dev/mapper/centos-root -t 19703808k Opening file: /dev/mapper/centos-root File information: ID of device containing file: 5 inode number: 2006 protection: 60660 (block device) number of hard links: 1 user ID of owner: 0 group ID of owner: 6 device ID (if special file): 64768 blocksize for filesystem I/O: 4096 number of blocks allocated: 0 time of last access: 1533986548 Sat Aug 11 07:22:28 2018 time of last modification: 1533984737 Sat Aug 11 06:52:17 2018 time of last status change: 1533984737 Sat Aug 11 06:52:17 2018 total size, in bytes: 0 (0.000 exp(+0)) Size to process: 20176699392 (18.791 GiB) Opening file: /dev/mapper/centos-root File information: ID of device containing file: 5 inode number: 2006 protection: 60660 (block device) number of hard links: 1 user ID of owner: 0 group ID of owner: 6 device ID (if special file): 64768 blocksize for filesystem I/O: 4096 number of blocks allocated: 0 time of last access: 1533986548 Sat Aug 11 07:22:28 2018 time of last modification: 1533984737 Sat Aug 11 06:52:17 2018 time of last status change: 1533984737 Sat Aug 11 06:52:17 2018 total size, in bytes: 0 (0.000 exp(+0)) Size to process: 20176699392 (18.791 GiB) Worker(0): 1.16% done. 2018-08-13 20:20:29 ETA(in 00:06:06). Processing speed: 25.949 MiB/sec Worker(1): 1.16% done. 2018-08-13 20:22:01 ETA(in 00:07:37). Processing speed: 20.766 MiB/sec Worker(0): 2.24% done. 2018-08-13 20:20:29 ETA(in 00:06:02). Processing speed: 25.949 MiB/sec Worker(1): 2.24% done. 2018-08-13 20:25:05 ETA(in 00:10:34). Processing speed: 14.828 MiB/sec Worker(0): 3.32% done. 2018-08-13 20:23:30 ETA(in 00:08:57). Processing speed: 17.300 MiB/sec Worker(1): 3.32% done. 2018-08-13 20:20:33 ETA(in 00:05:58). Processing speed: 25.957 MiB/sec Worker(0): 4.40% done. 2018-08-13 20:22:01 ETA(in 00:07:23). Processing speed: 20.760 MiB/sec Worker(1): 4.40% done. 2018-08-13 20:20:33 ETA(in 00:05:54). Processing speed: 25.949 MiB/sec Worker(0): 5.48% done. 2018-08-13 20:20:32 ETA(in 00:05:50). Processing speed: 25.949 MiB/sec Worker(1): 5.48% done. 2018-08-13 20:22:02 ETA(in 00:07:18). Processing speed: 20.759 MiB/sec Worker(0): 6.56% done. 2018-08-13 20:22:00 ETA(in 00:07:13). Processing speed: 20.759 MiB/sec Worker(1): 6.56% done. 2018-08-13 20:20:34 ETA(in 00:05:46). Processing speed: 25.949 MiB/sec Worker(0): 7.64% done. 2018-08-13 20:20:33 ETA(in 00:05:42). Processing speed: 25.949 MiB/sec Worker(1): 7.64% done. 2018-08-13 20:20:34 ETA(in 00:05:42). Processing speed: 25.949 MiB/sec Worker(0): 8.71% done. 2018-08-13 20:19:07 ETA(in 00:04:13). Processing speed: 34.616 MiB/sec Worker(0): 9.80% done. 2018-08-13 20:16:18 ETA(in 00:01:23). Processing speed: 104.000 MiB/sec Worker(1): 8.71% done. 2018-08-13 20:19:08 ETA(in 00:04:13). Processing speed: 34.599 MiB/sec Worker(0): 11.21% done. 2018-08-13 20:15:58 ETA(in 00:01:02). Processing speed: 136.000 MiB/sec Worker(1): 9.79% done. 2018-08-13 20:19:08 ETA(in 00:04:10). Processing speed: 34.599 MiB/sec Worker(0): 12.29% done. 2018-08-13 20:20:25 ETA(in 00:05:25). Processing speed: 25.953 MiB/sec Worker(1): 10.87% done. 2018-08-13 20:19:08 ETA(in 00:04:07). Processing speed: 34.599 MiB/sec Worker(1): 11.95% done. 2018-08-13 20:19:08 ETA(in 00:04:04). Processing speed: 34.605 MiB/sec Worker(0): 13.37% done. 2018-08-13 20:23:07 ETA(in 00:08:01). Processing speed: 17.299 MiB/sec Worker(1): 13.03% done. 2018-08-13 20:19:08 ETA(in 00:04:01). Processing speed: 34.599 MiB/sec
# ./stream_parser -f /opt/data/mysql_3306/ibdata1
扫描完之后，会在当前目录下生成相关的目录：
四，找出assets_host_auth表数据所在的磁盘页。
1，找出assets_host_auth的表ID：
./c_parser -4Df ./pages-ibdata1/FIL_PAGE_INDEX/0000000000000001.page -t ./dictionary/SYS_TABLES.sql | grep assets
000000002D0A 2A0000017E28FC SYS_TABLES "iceny/assets\_host\_auth" 185 4 33 0 80 "" 178
SET FOREIGN_KEY_CHECKS=0;
LOAD DATA LOCAL INFILE '/tmp/undrop-for-innodb-master/dumps/default/SYS_TABLES000000002D0A 2A0000017E28FC SYS_TABLES "iceny/assets\_host\_auth" 185 4 33 080 "" 178
' 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`);
-- STATUS {"records_expected": 122, "records_dumped": 34, "records_lost": true} STATUS END 表ID为表名后面的那个数字，这里为185。
2，利用找出来的表ID，查找assets_host_auth的磁盘页ID：
# ./c_parser -4Df ./pages-ibdata1/FIL_PAGE_INDEX/0000000000000003.page -t ./dictionary/SYS_INDEXES.sql | grep 185 000000002D0A 2A0000017E27EB SYS_INDEXES 185 335 "PRIMARY" 1 3 178 4294967295 000000001140 2500000139185D SYS_INDEXES 119 207 "PRIMARY" 1 3 105 4294967295 000000002D0A 2A0000017E27EB SYS_INDEXES 185 335 "PRIMARY" 1 3 178 4294967295 000000001140 2500000139185D SYS_INDEXES 119 207 "PRIMARY" 1 3 105 4294967295 SET FOREIGN_KEY_CHECKS=0;
这里可以明细那看到，ID185对应的数值是335，这里的335就是assets_host_auth数据所在的的磁盘页ID。
3，查看扫描的磁盘页中是否存在335的page：
# ll pages-centos-root/FIL_PAGE_INDEX/0000000000000335.page -rw-r--r-- 1 root root 65536 Aug 13 20:31 pages-centos-root/FIL_PAGE_INDEX/0000000000000335.page
可以看到335page确实存在。
4，创建assets_host_auth.sql文件，内容是assets_host_auth表的数据结构：
# vi iceny/assets_host_auth.sql CREATE TABLE `assets_host_auth` ( `id` int(11) NOT NULL AUTO_INCREMENT, `host_ip` varchar(20) NOT NULL, `password` varchar(100) DEFAULT NULL, `env` varchar(20) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=22 DEFAULT CHARSET=utf8;
5，利用存在的磁盘page查看assets_host_auth数据是否还在；
./c_parser -6f pages-centos-root/FIL_PAGE_INDEX/0000000000000335.page -t iceny/assets_host_auth.sql | head -5 -- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (5 5) 000000002690 DF000001C10110 assets_host_auth 1 "192.168.204.128" "123456" "cmh\_test" 000000002690 DF000001C1011D assets_host_auth 17 "192.168.1.11" "]t;:<8qCLfse+8LZZhK+11" "HB" 000000002690 DF000001C1012A assets_host_auth 19 "192.168.1.12" "]t;:<8qCLfse+8LZZhK+12" "HB" 000000002690 DF000001C10137 assets_host_auth 20 "192.168.1.113" "]t;:<8qCLfse+8LZZhK+113" "HB"
这里可以看到找到了一些相关的数据。
6，导出数据，生成sql导入文件：
# ./c_parser -6f pages-centos-root/FIL_PAGE_INDEX/0000000000000335.page -t iceny/assets_host_auth.sql > dumps/default/assets_host_auth 2> dumps/default/assets_host_auth.sql
# more dumps/default/assets_host_auth.sql
SET FOREIGN_KEY_CHECKS=0;
LOAD DATA LOCAL INFILE '/tmp/undrop-for-innodb-master/dumps/default/assets_host_auth' REPLACE INTO TABLE `assets_host_auth` FIELDS TERMINATED BY '\t' OPTIONALLY ENCLOSED BY '"' LINES STA
RTING BY 'assets_host_auth\t' (`id`, `host_ip`, `password`, `env`);
-- STATUS {"records_expected": 20, "records_dumped": 20, "records_lost": false} STATUS END
# more /tmp/undrop-for-innodb-master/dumps/default/assets_host_auth
-- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (5 5)
000000002690 DF000001C10110 assets_host_auth 1 "192.168.204.128" "123456" "cmh\_test"
000000002690 DF000001C1011D assets_host_auth 17 "192.168.1.11" "]t;:<8qCLfse+8LZZhK+11" "HB"
000000002690 DF000001C1012A assets_host_auth 19 "192.168.1.12" "]t;:<8qCLfse+8LZZhK+12" "HB"
000000002690 DF000001C10137 assets_host_auth 20 "192.168.1.113" "]t;:<8qCLfse+8LZZhK+113" "HB"
000000002690 DF000001C10144 assets_host_auth 21 "192.168.1.15" "]t;:<8qCLfse+8LZZhK+15" "HB"
-- Page id: 3, Found records: 5, Lost records: NO, Leaf page: YES
-- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (5 5)
000000002690 DF000001C10110 assets_host_auth 1 "192.168.204.128" "123456" "cmh\_test"
000000002690 DF000001C1011D assets_host_auth 17 "192.168.1.11" "]t;:<8qCLfse+8LZZhK+11" "HB"
000000002690 DF000001C1012A assets_host_auth 19 "192.168.1.12" "]t;:<8qCLfse+8LZZhK+12" "HB"
000000002690 DF000001C10137 assets_host_auth 20 "192.168.1.113" "]t;:<8qCLfse+8LZZhK+113" "HB"
000000002690 DF000001C10144 assets_host_auth 21 "192.168.1.15" "]t;:<8qCLfse+8LZZhK+15" "HB"
-- Page id: 3, Found records: 5, Lost records: NO, Leaf page: YES
-- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (5 5)
000000002690 DF000001C10110 assets_host_auth 1 "192.168.204.128" "123456" "cmh\_test"
000000002690 DF000001C1011D assets_host_auth 17 "192.168.1.11" "]t;:<8qCLfse+8LZZhK+11" "HB"
000000002690 DF000001C1012A assets_host_auth 19 "192.168.1.12" "]t;:<8qCLfse+8LZZhK+12" "HB"
000000002690 DF000001C10137 assets_host_auth 20 "192.168.1.113" "]t;:<8qCLfse+8LZZhK+113" "HB"
000000002690 DF000001C10144 assets_host_auth 21 "192.168.1.15" "]t;:<8qCLfse+8LZZhK+15" "HB"
-- Page id: 3, Found records: 5, Lost records: NO, Leaf page: YES
-- Page id: 3, Format: COMPACT, Records list: Valid, Expected records: (5 5)
000000002690 DF000001C10110 assets_host_auth 1 "192.168.204.128" "123456" "cmh\_test"
000000002690 DF000001C1011D assets_host_auth 17 "192.168.1.11" "]t;:<8qCLfse+8LZZhK+11" "HB"
000000002690 DF000001C1012A assets_host_auth 19 "192.168.1.12" "]t;:<8qCLfse+8LZZhK+12" "HB"
000000002690 DF000001C10137 assets_host_auth 20 "192.168.1.113" "]t;:<8qCLfse+8LZZhK+113" "HB"
000000002690 DF000001C10144 assets_host_auth 21 "192.168.1.15" "]t;:<8qCLfse+8LZZhK+15" "HB"
-- Page id: 3, Found records: 5, Lost records: NO, Leaf page: YES 可以看到，我们已经找回了我们所删除的数据，最后要做的，就是把这些数据导入数据库中去：
7，把数据导入数据库：
#导入表结构 mysql> use iceny; Database changed mysql> source /tmp/undrop-for-innodb-master/iceny/assets_host_auth.sql Query OK, 0 rows affected (0.21 sec)
导入数据，并查看：
对比之前的数据，发现并无差异，至此，我们就通过undrop-for-innodb工具在无备份的情况下找回了数据。
undrop-for-innodb的一些问题（个人猜想）
由于undrop-for-innodb是通过扫描磁盘页来找回数据的，所以在删除表的一定短时间内，来用这种方法来找回数据是可行的。若是时间过长，磁盘页由于大量的IO操作，导致刷新了，有可能数据就被刷新掉了，这时候能不能找回数据，就不一定了。所以，在发现执行了误操作后，应立即停止mysql，把数据磁盘挂载为只读模式，避免数据页被刷新。