最初的測評

昨天，我看到一個(gè)非常有趣的刪除一個(gè)目錄下的海量文件的方法。這個(gè)方法來自http://www.quora.com/How-can-someone-rapidly-delete-400-000-files里的Zhenyu Lee。

他沒有使用find 或 xargs，他很有創(chuàng)意的利用了rsync的強(qiáng)大功能，使用rsync –delete將目標(biāo)文件夾以一個(gè)空文件夾來替換。之后，我做了一個(gè)實(shí)驗(yàn)來比較各種方法。讓我吃驚的是，Lee的方法要比其它的快的多。下面就是我的測評。

環(huán)境：

• CPU: Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz
• MEM: 4G
• HD: ST3250318AS: 250G/7200RPM

使用 –delete 和 –exclude，你可以選擇性刪除符合條件的文件。還有一點(diǎn)，當(dāng)你需要保留這個(gè)目錄做其它用處時(shí)，這種方法是再適合不過了。

重新測評

幾天前，Keith-Winstein在回復(fù)Quora上的這個(gè)帖子時(shí)說我之前的測評無法復(fù)制，因?yàn)椴僮鞯臅r(shí)間持續(xù)的太久。我澄清一下，這些數(shù)據(jù)過大，可能是因?yàn)槲业挠?jì)算機(jī)在過去的幾年里做的事太多，測評中可能存在一些文件系統(tǒng)錯(cuò)誤。但我不確定是這些原因。現(xiàn)在好了，我弄了一天比較新的計(jì)算機(jī)，把測評再做一次。這次我使用/usr/bin/time，它能提供更詳細(xì)的信息。下面就是新的結(jié)果。

(每次都是1000000個(gè)文件。每個(gè)文件的體積都是0。)

原始輸出

# 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

我真的十分好奇為什么Lee的方法要比其它的快，竟然比rm -rf也要快。如果有人知道，請寫在下面，非常感謝。

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