回收站简介
在HDFS里，删除文件时，不会真正的删除，其实是放入回收站/trash
回收站里的文件可以快速恢复。
可以设置一个时间阈值，当回收站里文件的存放时间超过这个阈值或是回收站被清空时，文件才会被彻底删除，并且释放占用的数据块。
hadoop 的回收站trash功能默认是关闭的，所以需要在core-site.xml中手动开启
--手动开启trash功能，添加fs.trash.interval属性
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls /user/grid/.Trash
ls: Cannot access /user/grid/.Trash: No such file or directory.
[grid@rac2 hadoop-0.20.2]$ vi conf/core-site.xml
<property>
<name>fs.trash.interval</name>
<value>1440</value>
<description>Number of minutes between trash checkpoints.
If zero, the trash feature is disabled.
</description>
</property>
注：fs.trash.interval 的含义是文件删除后保留时长，默认为0，单位为分钟，这里设的是1天（60*24）
--测试删除数据
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls in
Found 2 items
-rw-r--r-- 2 grid supergroup 12 2012-11-26 15:31 /user/grid/in/test1.txt
-rw-r--r-- 2 grid supergroup 13 2012-11-26 15:31 /user/grid/in/test2.txt
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -rmr in
Moved to trash: hdfs://gc:9000/user/grid/in
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -rm abc
Moved to trash: hdfs://gc:9000/user/grid/abc
--检查回收站数据，发现多出了.Trash目录
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls /user/grid/.Trash
Found 1 items
drwxr-xr-x - grid supergroup 0 2012-11-28 15:49 /user/grid/.Trash/Current
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls /user/grid/.Trash/Current
Found 1 items
drwxr-xr-x - grid supergroup 0 2012-11-28 15:49 /user/grid/.Trash/Current/user
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls /user/grid/.Trash/Current/user
Found 1 items
drwx------ - grid supergroup 0 2012-11-28 15:50 /user/grid/.Trash/Current/user/grid
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls /user/grid/.Trash/Current/user/grid
Found 2 items
-rw-r--r-- 2 grid supergroup 0 2012-11-27 14:04 /user/grid/.Trash/Current/user/grid/abc
drwxr-xr-x - grid supergroup 0 2012-11-26 15:31 /user/grid/.Trash/Current/user/grid/in
注：在HDFS上的回收站数据在 /user/$USER/.Trash/Current/user/$USER/目录下
--恢复回收站数据
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -mv /user/grid/.Trash/Current/user/grid/in /user/grid/in
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls in
Found 2 items
-rw-r--r-- 2 grid supergroup 12 2012-11-26 15:31 /user/grid/in/test1.txt
-rw-r--r-- 2 grid supergroup 13 2012-11-26 15:31 /user/grid/in/test2.txt
--清空回收站
清空回收站命令：hdfs dfs -expunge
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls .Trash/Current/user/grid
Found 1 items
-rw-r--r-- 2 grid supergroup 0 2012-11-27 14:04 /user/grid/.Trash/Current/user/grid/abc
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -expunge
12/11/28 16:09:12 INFO fs.Trash: Created trash checkpoint: /user/grid/.Trash/1211281609
[grid@rac2 hadoop-0.20.2]$ bin/hadoop dfs -ls .Trash/Current/user/grid
ls: Cannot access .Trash/Current/user/grid: No such file or directory.
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