Linux技巧：一次删除一百万个文件的最快方法

最初的测评

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 –delete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 FilesDeletion Timersync -a –delete empty/ s1/10000006m50.638sfind s2/ -type f -delete100000087m38.826sfind s3/ -type f | xargs -L 100 rm100000083m36.851sfind s4/ -type f | xargs -L 100 -P 100 rm100000078m4.658srm -rf s5100000080m33.434s

使用 –delete 和 –exclude，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。)

CommandElapsedSystem Time%CPUcs (Vol/Invol)rsync -a –delete empty/ a10.601.3195106/22find b/ -type f -delete28.5114.465214849/11find c/ -type f | xargs -L 100 rm41.6920.605437048/15074find d/ -type f | xargs -L 100 -P 100 rm34.3227.8289929897/21720rm -rf f31.2914.804715134/11

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 3find 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 4find 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。

[英文原文： A faster way to delete millions of files in a directory ]