Invoke-WebRequest / getElementsByTagName is incredibly slow on some machines by DanTup

Active

Type:	Bug
ID:	778371
Opened:	2/2/2013 11:00:00 AM
Access Restriction:	Public

Workaround(s)

view

User(s) can reproduce this bug

I've posted full details and a sample on StackOverflow here:

http://stackoverflow.com/questions/14202054/why-is-this-powershell-code-invoke-webrequest-getelementsbytagname-so-incred/14657508?iemail=1

I have some code that uses Invoke-WebRequest to fetch a web page, and then use .ParsedHtml.body.getElementsByTagName to scrape some info from the site.

However, the getElementsByTagName call seems to take a *long* time for me (around 1.5seconds per call) on all three machines I've tested it on (Windows 7 Home Premium, Windows 7 Enterprise, Windows 8). Other people see sub-100 millisecond times running the same code.

There's more discussion about this issue on Google+ here:
https://plus.google.com/communities/114336958783305019912

I can't find any common pattern between machines that do/don't have this issue. It occurs for me with no PS profile, in both ISE and the console. I have VS 2012 (and therefore .NET 4.5) installed on two of the machines, but not the third.

Details (expand)

Always Happens

I don't know if this issue existed previously

Run the following code:

$url = "http://www.icy-veins.com/restoration-shaman-wow-pve-healing-gear-loot-best-in-slot"
$response = (iwr $url).ParsedHtml

# Loop through the h2 tags
$response.body.getElementsByTagName("h2") | foreach {

    # Get the table that comes after the heading
    $slotTable = $_.nextSibling

    # Grab the rows from the table, skipping the first row (column headers)
    measure-command { $rows = $slotTable.getElementsByTagName("tr") | select -Skip 1 } | select TotalMilliseconds
}

Except to get short times, like this sample from somebody in the Google+ Community:

TotalMilliseconds
-----------------
         76.9098
         112.6745
         56.6522
         140.5845
         84.9599
         48.6669
         79.9283
         73.4511
         94.0683
         81.4443
         147.809
         139.2805
         111.4078
         56.3881
         41.3386

However, I get this:

TotalMilliseconds
-----------------
        1575.7633
        2371.5566
        1073.7552
        2307.8844
        1779.5518
        1063.9977
        1588.5112
        1372.4927
        1248.7245
        1718.3555
         3283.843
        2931.1616
        2557.8595
        1230.5093
         995.2934

0 attachments

Microsoft