linux技巧：一次刪除一百萬個檔案的最快方法

最初的評估

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: 250RPG/7200%

Deletion Time

rsync -a –delete empty/ s1/    1000000    6m50.638s    

find s2/ -type f -200

find s3/ -type f | xargs -L 100 rm    1000000    83m36.851s

find s4/ -type f | xargs -L 100 -P 100 rm    1000000    78m4.658s     

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。

重新評估

幾天前，Keith-Winstein在回覆Quora上的這個貼文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，這些數據過大，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

%CPUEapsed

System Time

%CPU🜎 -a –delete empty/ a    10.60    1.31    95    106/22    

find b/ -type f -delete   28.51121    

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    89    929897/21720    89    929897/21720    89    929897/21720    89    929897/21720    89 中時 f 47    15134/11    

原輸出

# 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