PowerShell Memory leak misunderstanding

问题:

New to PowerShell, so kind of learning by doing.

The process I have created works, but it ends up locking down my machine until it is completed, eating up all memory. I thought I had this fixed by looking into forcing the garbage collector, and also moving from a for-each statement to using %() to loop through everything.

Quick synopsis of process: Need to merge multiple SharePoint log files into single ones to track usage across all of the companies' different SharePoint sites. PowerShell loops through all log directories on the SP server, and checks each file in the directory if it already exists on my local machine. If it does exist it appends the file text, otherwise it does a straight copy. Rinse-repeat for each file and directory on the SharePoint Log server. Between each loop, I'm forcing the GC because... Well because my basic understanding is the looped variables are held in memory, and I want to flush them. I'm probably looking at this all wrong. So here is the script in question.

$FinFiles = 'F:\Monthly Logging\Logs'

dir -path '\\SP-Log-Server\Log-Directory' | ?{$_.PSISContainer} | %{
    $CurrentDir = $_
    dir $CurrentDir.FullName | ?(-not $_.PSISContainer} | %{
        if($_.Extension -eq ".log"){
            $DestinationFile = $FinFiles + '\' + $_.Name
            if((Test-Path $DestinationFile) -eq $false){
                New-Item -ItemType file -path $DestinationFile -Force
                Copy-Item $_.FullName $DestinationFile
            }
            else{
                $A = Get-Content $_.FullName ; Add-Content $DestinationFile $A
                Write-Host "Log File"$_.FullName"merged."
            }
        [GC]::Collect()
    }
    [GC]::Collect()
}

Granted the completed/appended log files get very very large (min 300 MB, max 1GB). Am I not closing something I should be, or keeping something open in memory? (It is currently sitting at 7.5 of my 8 Gig memory total.)

Thanks in advance.

回答1:

Don't nest Get-ChildItem commands like that. Use wildcards instead. Try: dir "\\SP-Log-Server\Log-Directory\*\*.log" instead. That should improve things to start with. Then move this to a ForEach($X in $Y){} loop instead of a ForEach-Object{} loop (what you're using now). I'm betting that takes care of your problem.

So, re-written just off the top of my head:

$FinFiles = 'F:\Monthly Logging\Logs'

ForEach($LogFile in (dir -path '\\SP-Log-Server\Log-Directory\*\*.log')){
    $DestinationFile = $FinFiles + '\' + $LogFile.Name
        if((Test-Path $DestinationFile) -eq $false){
            New-Item -ItemType file -path $DestinationFile -Force
            Copy-Item $LogFile.FullName $DestinationFile
        }
        else{
            $A = Get-Content $LogFile.FullName ; Add-Content $DestinationFile $A
            Write-Host "Log File"$LogFile.FullName"merged."
        }
    }
}

Edit: Oh, right, Alexander Obersht may be quite right as well. You may well benefit from a StreamReader approach as well. At the very least you should use the -readcount argument to Get-Content, and there's no reason to save it as a variable, just pipe it right to the add-content cmdlet.

Get-Content $LogFile.FullName -ReadCount 5000| Add-Content $DestinationFile

To explain my answer a little more, if you use ForEach-Object in the pipeline it keeps everything in memory (regardless of your GC call). Using a ForEach loop does not do this, and should take care of your issue.

回答2:

You might find this and this helpful.

In short: Add-Content, Get-Content and Out-File are convenient but notoriously slow when you need to deal with large amounts of data or I/O operations. You want to fall back to StreamReader and StreamWriter .NET classes for performance and/or memory usage optimization in cases like yours.

Code sample:

$sInFile = "infile.txt"
$sOutFile = "outfile.txt"

$oStreamReader = New-Object -TypeName System.IO.StreamReader -ArgumentList @($sInFile)
# $true sets append mode.
$oStreamWriter = New-Object -TypeName System.IO.StreamWriter -ArgumentList @($sOutFile, $true)

foreach ($sLine in $oStreamReader.ReadLine()) {
    $oStreamWriter.WriteLine($sLine)
}

$oStreamReader.Close()
$oStreamWriter.Close()