Linux技巧：一次删除一百万个文件的最快方法

昨天，我看到一个非常有趣的删除一个目录下的海量文件的方法。这个方法来自http://www.quora.com/How-can-someone-rapidly-delete-400-000-files里的Zhenyu Lee。

他没有使用find 或 xargs，他很有创意的利用了rsync的强大功能，使用rsync �Cdelete将目标文件夹以一个空文件夹来替换。之后，我做了一个实验来比较各种方法。让我吃惊的是，Lee的方法要比其它的快的多。下面就是我的测评。

环境：

• CPU: Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz

• MEM: 4G

• HD: ST3250318AS: 250G/7200RPM

Method	# Of Files	Deletion Time
rsync -a �Cdelete empty/ s1/	1000000	6m50.638s
find s2/ -type f -delete	1000000	87m38.826s
find s3/ -type f | xargs -L 100 rm	1000000	83m36.851s
find s4/ -type f | xargs -L 100 -P 100 rm	1000000	78m4.658s
rm -rf s5	1000000	80m33.434s

使用 �Cdelete 和 �Cexclude，你可以选择性删除符合条件的文件。还有一点，当你需要保留这个目录做其它用处时，这种方法是再适合不过了。

重新测评

几天前，Keith-Winstein在回复Quora上的这个帖子时说我之前的测评无法复制，因为操作的时间持续的太久。我澄清一下，这些数据过大，可能是因为我的计算机在过去的几年里做的事太多，测评中可能存在一些文件系统错误。但我不确定是这些原因。现在好了，我弄了一天比较新的计算机，把测评再做一次。这次我使用/usr/bin/time，它能提供更详细的信息。下面就是新的结果。

(每次都是1000000个文件。每个文件的体积都是0。)

Command	Elapsed	System Time	%CPU	cs (Vol/Invol)
rsync -a �Cdelete empty/ a	10.60	1.31	95	106/22
find b/ -type f -delete	28.51	14.46	52	14849/11
find c/ -type f | xargs -L 100 rm	41.69	20.60	54	37048/15074
find d/ -type f | xargs -L 100 -P 100 rm	34.32	27.82	89	929897/21720
rm -rf f	31.29	14.80	47	15134/11

原始输出

# method 1
~/test $ /usr/bin/time -v  rsync -a --delete empty/ a/
        Command being timed: "rsync -a --delete empty/ a/"
        User time (seconds): 1.31
        System time (seconds): 10.60
        Percent of CPU this job got: 95%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:12.42
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 24378
        Voluntary context switches: 106
        Involuntary context switches: 22
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

# method 2
        Command being timed: "find b/ -type f -delete"
        User time (seconds): 0.41
        System time (seconds): 14.46
        Percent of CPU this job got: 52%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:28.51
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 11749
        Voluntary context switches: 14849
        Involuntary context switches: 11
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0
# method 3
find c/ -type f | xargs -L 100 rm
~/test $ /usr/bin/time -v ./delete.sh
        Command being timed: "./delete.sh"
        User time (seconds): 2.06
        System time (seconds): 20.60
        Percent of CPU this job got: 54%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:41.69
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 1764225
        Voluntary context switches: 37048
        Involuntary context switches: 15074
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

# method 4
find d/ -type f | xargs -L 100 -P 100 rm
~/test $ /usr/bin/time -v ./delete.sh
        Command being timed: "./delete.sh"
        User time (seconds): 2.86
        System time (seconds): 27.82
        Percent of CPU this job got: 89%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:34.32
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 1764278
        Voluntary context switches: 929897
        Involuntary context switches: 21720
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

# method 5
~/test $ /usr/bin/time -v rm -rf f
        Command being timed: "rm -rf f"
        User time (seconds): 0.20
        System time (seconds): 14.80
        Percent of CPU this job got: 47%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:31.29
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 176
        Voluntary context switches: 15134
        Involuntary context switches: 11
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

我真的十分好奇为什么Lee的方法要比其它的快，竟然比rm -rf也要快。如果有人知道，请写在下面，非常感谢。