Linux技巧:一次刪除一百萬個檔案的最快方法

aqee發表於2013-06-13

  最初的測評

  昨天,我看到一個非常有趣的刪除一個目錄下的海量檔案的方法。這個方法來自http://www.quora.com/How-can-someone-rapidly-delete-400-000-files裡的Zhenyu Lee。

  他沒有使用find 或 xargs,他很有創意的利用了rsync的強大功能,使用rsync –delete將目標資料夾以一個空資料夾來替換。之後,我做了一個實驗來比較各種方法。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,你可以選擇性刪除符合條件的檔案。還有一點,當你需要保留這個目錄做其它用處時,這種方法是再適合不過了。

  重新測評

  幾天前,Keith-Winstein在回覆Quora上的這個帖子時說我之前的測評無法複製,因為操作的時間持續的太久。我澄清一下,這些資料過大,可能是因為我的計算機在過去的幾年裡做的事太多,測評中可能存在一些檔案系統錯誤。但我不確定是這些原因。現在好了,我弄了一天比較新的計算機,把測評再做一次。這次我使用/usr/bin/time,它能提供更詳細的資訊。下面就是新的結果。

  (每次都是1000000個檔案。每個檔案的體積都是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麼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

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