Linux技巧：一次刪除一百萬個文件最快方法

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

他沒有使用find 或 xargs，他很有創意的利用了rsync的強大功能，使用rsync –delete將目標文件夾以一個空文件夾來替換。之后，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

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使用 –delete 和 –exclude，你可以選擇性刪除符合條件的文件。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在回復Quora上的這個帖子時說我之前的測評無法復制，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里做的事太多，測評中可能存在一些文件系統錯誤。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，它能提供更詳細的信息。下面就是新的結果。

(每次都是1000000個文件。每個文件的體積都是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

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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): 1.31System time (seconds): 10.60Percent of CPU this job got: 95%Elapsed (wall clock) time (h:mm:ss or m:ss): 0:12.42Average shared text size (kbytes): 0Average unshared data size (kbytes): 0Average stack size (kbytes): 0Average total size (kbytes): 0Maximum resident set size (kbytes): 0Average resident set size (kbytes): 0Major (requiring I/O) page faults: 0Minor (reclaiming a frame) page faults: 24378Voluntary context switches: 106Involuntary context switches: 22Swaps: 0File system inputs: 0File system outputs: 0Socket messages sent: 0Socket messages received: 0Signals delivered: 0Page size (bytes): 4096Exit status: 0# method 2Command being timed: "find b/ -type f -delete"User time (seconds): 0.41System time (seconds): 14.46Percent of CPU this job got: 52%Elapsed (wall clock) time (h:mm:ss or m:ss): 0:28.51Average shared text size (kbytes): 0Average unshared data size (kbytes): 0Average stack size (kbytes): 0Average total size (kbytes): 0Maximum resident set size (kbytes): 0Average resident set size (kbytes): 0Major (requiring I/O) page faults: 0Minor (reclaiming a frame) page faults: 11749Voluntary context switches: 14849Involuntary context switches: 11Swaps: 0File system inputs: 0File system outputs: 0Socket messages sent: 0Socket messages received: 0Signals delivered: 0Page size (bytes): 4096Exit status: 0
# method 3
find c/ -type f | xargs -L 100 rm
~/test $ /usr/bin/time -v ./delete.shCommand being timed: "./delete.sh"User time (seconds): 2.06System time (seconds): 20.60Percent of CPU this job got: 54%Elapsed (wall clock) time (h:mm:ss or m:ss): 0:41.69Average shared text size (kbytes): 0Average unshared data size (kbytes): 0Average stack size (kbytes): 0Average total size (kbytes): 0Maximum resident set size (kbytes): 0Average resident set size (kbytes): 0Major (requiring I/O) page faults: 0Minor (reclaiming a frame) page faults: 1764225Voluntary context switches: 37048Involuntary context switches: 15074Swaps: 0File system inputs: 0File system outputs: 0Socket messages sent: 0Socket messages received: 0Signals delivered: 0Page size (bytes): 4096Exit status: 0# method 4
find d/ -type f | xargs -L 100 -P 100 rm
~/test $ /usr/bin/time -v ./delete.shCommand being timed: "./delete.sh"User time (seconds): 2.86System time (seconds): 27.82Percent of CPU this job got: 89%Elapsed (wall clock) time (h:mm:ss or m:ss): 0:34.32Average shared text size (kbytes): 0Average unshared data size (kbytes): 0Average stack size (kbytes): 0Average total size (kbytes): 0Maximum resident set size (kbytes): 0Average resident set size (kbytes): 0Major (requiring I/O) page faults: 0Minor (reclaiming a frame) page faults: 1764278Voluntary context switches: 929897Involuntary context switches: 21720Swaps: 0File system inputs: 0File system outputs: 0Socket messages sent: 0Socket messages received: 0Signals delivered: 0Page size (bytes): 4096Exit status: 0# method 5
~/test $ /usr/bin/time -v rm -rf fCommand being timed: "rm -rf f"User time (seconds): 0.20System time (seconds): 14.80Percent of CPU this job got: 47%Elapsed (wall clock) time (h:mm:ss or m:ss): 0:31.29Average shared text size (kbytes): 0Average unshared data size (kbytes): 0Average stack size (kbytes): 0Average total size (kbytes): 0Maximum resident set size (kbytes): 0Average resident set size (kbytes): 0Major (requiring I/O) page faults: 0Minor (reclaiming a frame) page faults: 176Voluntary context switches: 15134Involuntary context switches: 11Swaps: 0File system inputs: 0File system outputs: 0Socket messages sent: 0Socket messages received: 0Signals delivered: 0Page size (bytes): 4096Exit 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 ]