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 files
deletion time
rsync -a –delete 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 –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。)
command
elapsed
system time
%cpu
cs (vol/invol)
rsync -a –delete 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