提高Powershell性能以生成随机文件 [英] Improve Powershell Performance to Generate a Random File
问题描述
我想让Powershell用户创建一个随机文本文件以用于基本系统测试(上传，下载，校验和等). 我已使用以下文章并提供了自己的代码段来创建随机文本文件，但性能却很糟糕.
I'd like to user Powershell to create a random text file for use in basic system testing (upload, download, checksum, etc). I've used the following articles and come up with my own code snippet to create a random text file but the performance is terrible.
- 在Windows中生成随机文件(stackoverflow.com)
- PowerShell –创建虚拟文件(verboon.信息)
- 使用Powershell创建大文件(基于上面的动词代码的chris-nullpayload.rhcloud.com)
- Generating Random Files in Windows (stackoverflow.com)
- PowerShell – Creating Dummy files (verboon.info)
- Create large files with Powershell (chris-nullpayload.rhcloud.com based on verboon code above)
这是我的代码示例，在现代Windows 7 Dell笔记本电脑上，该代码示例大约需要227秒才能生成1MB的随机文本文件.运行时间是使用Measure-Command cmdlet确定的.我在不同的系统负载下重复了几次测试，并获得了相似的长时间运行结果.
Here is my code sample that takes approximately 227 seconds to generate a 1MB random text file on a modern Windows 7 Dell laptop. Run time was determined using the Measure-Command cmdlet. I repeated the test several times during different system load with similar long runtime results.
# select characters from 0-9, A-Z, and a-z
$chars = [char[]] ([char]'0'..[char]'9' + [char]'A'..[char]'Z' + [char]'a'..[char]'z')
# write file using 128 byte lines each with 126 random characters
1..(1mb/128) | %{-join (1..126 | %{get-random -InputObject $chars }) } `
| out-file test.txt -Encoding ASCII
我正在寻找讨论为什么此代码的性能较差的答案，以及针对我可以做出的简单更改以改善运行时间的建议，以生成类似的随机文本文件( 126个随机字母数字字符的ASCII文本行-带"\ r \ n" EOL的128个字节，输出文件为偶数个兆字节，例如上面的1MB示例).我希望将文件输出分段(每次一行或多行)，这样我们就不再需要存储在内存中的输出文件大小的字符串了.
I am looking for answers that discuss why this code has poor performance and suggestions for simple changes I can make to improve the runtime for generating a similar random text file (ASCII text lines of 126 random alphanumeric characters - 128 bytes with "\r\n" EOL, output file an even number of megabytes such as the above 1MB sample). I would like file output to be written in pieces (one or more lines at a time) so that we never need a string the size of the output file stored in memory.
推荐答案
同意@dugas瓶颈正在为每个字符调用Get-Random.
Agree with @dugas that the bottleneck is calling Get-Random for every character.
如果增加字符数组集并使用Get-Random的-count属性，则应该能够实现几乎相同的随机性.
You should be able to achieve nearly the same randomness if you increase your character array set, and use the -count property of Get-Random.
如果您使用的是V4，则.foreach方法要比foreach-object快得多.
If you have V4, the .foreach method is considerably faster than foreach-object.
也将Out-File换为Add-Content，这也应该有所帮助.
Also traded Out-File for Add-Content, which should also help.
# select characters from 0-9, A-Z, and a-z
$chars = [char[]] ([char]'0'..[char]'9' + [char]'A'..[char]'Z' + [char]'a'..[char]'z')
$chars = $chars * 126
# write file using 128 byte lines each with 126 random characters
(1..(1mb/128)).foreach({-join (Get-Random $chars -Count 126) | add-content testfile.txt })
这在我的系统上完成了大约32秒.
That finished in about 32 seconds on my system.
使用生成的测试文件设置内容vs外文件:
Set-Content vs Out-File, using the generated test file:
$x = Get-Content testfile.txt
(Measure-Command {$x | out-file testfile1.txt}).totalmilliseconds
(Measure-Command {$x | Set-Content testfile1.txt}).totalmilliseconds
504.0069
159.0842
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