运行在容器里的 MySQL 删除数据目录依然可以正常使用？

[awker]

运行在容器里的 MySQL 删除数据目录依然可以正常使用，这是什么原因？ 同样的步骤在虚拟机操作，MySQL 就无法正常使用。

操作步骤如下：

// 创建 mysql 挂载目录
root@aliyun:~#  mkdir /data/mysql

// 启动一个 mysql
root@aliyun:~#  docker run -p 3306:3306 -v /data/mysql:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=123456 -d mysql

root@aliyun:~#  docker ps
CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS          PORTS                               NAMES
5a27786e1657   mysql     "docker-entrypoint.s…"   32 seconds ago   Up 31 seconds   0.0.0.0:3306->3306/tcp, 33060/tcp   relaxed_jang

// 进入 mysql 容器
root@aliyun:~# docker exec -it 5a27786e1657 /bin/bash

root@5a27786e1657:/# ls /var/lib/mysql/
'#ib_16384_0.dblwr'   auto.cnf	      binlog.index   client-cert.pem   ib_logfile0   ibtmp1	 performance_schema   server-cert.pem   undo_001
'#ib_16384_1.dblwr'   binlog.000001   ca-key.pem     client-key.pem    ib_logfile1   mysql	 private_key.pem      server-key.pem    undo_002
'#innodb_temp'	      binlog.000002   ca.pem	     ib_buffer_pool    ibdata1	     mysql.ibd	 public_key.pem       sys
// 删除容器里的 mysql 数据目录
root@5a27786e1657:/# rm -rf /var/lib/mysql/
rm: cannot remove '/var/lib/mysql/': Device or resource busy
root@5a27786e1657:/# ls /var/lib/mysql/
root@5a27786e1657:/# exit

root@aliyun:~#  ifconfig eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 172.17.17.108  netmask 255.255.192.0  broadcast 172.17.63.255
        ether 00:16:3e:00:46:06  txqueuelen 1000  (Ethernet)
        RX packets 3678  bytes 638716 (638.7 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 3294  bytes 1044025 (1.0 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

root@aliyun:~# netstat -nltup|grep 3306
tcp        0      0 0.0.0.0:3306            0.0.0.0:*               LISTEN      1329/docker-proxy
// 删除 mysql 数据目录后，可以正常创建一个测试库 foobar
root@aliyun:~# mysql -uroot -p123456 -h172.17.17.108 -P 3306 -e "create database foobar;show databases;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+--------------------+
| Database           |
+--------------------+
| foobar             |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+

root@aliyun:~# ls /data/mysql/
foobar
root@aliyun:~# ls /data/mysql/foobar/
root@aliyun:~# 

[awker]

可以看到其实文件描述符还是存在的
# lsof -p 1405|grep deleted
mysqld 1405 999 9uW REG 252,1 50331648 1442005 /var/lib/mysql/ib_logfile1 (deleted)
mysqld 1405 999 10uW REG 252,1 196608 1442006 /var/lib/mysql/#ib_16384_0.dblwr (deleted)
mysqld 1405 999 11uW REG 252,1 8585216 1442007 /var/lib/mysql/#ib_16384_1.dblwr (deleted)
mysqld 1405 999 12uW REG 252,1 16777216 1442009 /var/lib/mysql/undo_001 (deleted)
mysqld 1405 999 13u REG 0,47 0 1442013 /tmp/ibI2pqU8 (deleted)
mysqld 1405 999 14uW REG 252,1 16777216 1442011 /var/lib/mysql/undo_002 (deleted)
mysqld 1405 999 15uW REG 252,1 12582912 1442015 /var/lib/mysql/ibtmp1 (deleted)
mysqld 1405 999 16uW REG 252,1 31457280 1442008 /var/lib/mysql/mysql.ibd (deleted)
mysqld 1405 999 24w REG 252,1 532 1442321 /var/lib/mysql/binlog.000002 (deleted)
mysqld 1405 999 26uW REG 252,1 81920 1442016 /var/lib/mysql/#innodb_temp/temp_1.ibt (deleted)
mysqld 1405 999 27uW REG 252,1 81920 1442017 /var/lib/mysql/#innodb_temp/temp_2.ibt (deleted)
mysqld 1405 999 28uW REG 252,1 81920 1442018 /var/lib/mysql/#innodb_temp/temp_3.ibt (deleted)
mysqld 1405 999 29uW REG 252,1 81920 1442019 /var/lib/mysql/#innodb_temp/temp_4.ibt (deleted)
mysqld 1405 999 30uW REG 252,1 81920 1442020 /var/lib/mysql/#innodb_temp/temp_5.ibt (deleted)
mysqld 1405 999 31uW REG 252,1 81920 1442021 /var/lib/mysql/#innodb_temp/temp_6.ibt (deleted)
mysqld 1405 999 32uW REG 252,1 81920 1442022 /var/lib/mysql/#innodb_temp/temp_7.ibt (deleted)
mysqld 1405 999 33uW REG 252,1 81920 1442023 /var/lib/mysql/#innodb_temp/temp_8.ibt (deleted)
mysqld 1405 999 34uW REG 252,1 81920 1442024 /var/lib/mysql/#innodb_temp/temp_9.ibt (deleted)
mysqld 1405 999 35uW REG 252,1 81920 1442315 /var/lib/mysql/#innodb_temp/temp_10.ibt (deleted)