This is a problem I've been having recently. I'm using a program to upload a file of around 150mb. This is going to take a while as my upload speed averages around 0.5mb.
However when I begin the upload I can no longer load webpages. I don't get an error. They just spend 10-15 minutes trying to load.
I've looked at activity monitor and when I'm not uploading the number of packers in/out is quite balanced usually 30-80 per sec. When I begin uploading my packets out skyrockets to several thousand per sec and my packets in drops below 10.
As far as I can tell it only happens with I'm uploading using this one program (Xcode). I uploaded a file through the browser to a different site yesterday and everything was fine.
This is a big problem for me. I need to do the upload but with my slow upload speed and the fact it's killing my download speed it takes my internet out of commission for hours. This is only a recent problem. I've been uploading files using Xcode for years with the same ISP.
Another data point which may be useful for diagnosing it the data received/sent per second. when uploading sent is 1.5mb and received is 15kb. When browsing and not uploading they are both between 100kb and 150kb (per sec).
Any ideas on what's causing this or even a workaround?
I'm currently uploading the same file to Dropbox and getting none of the same issues.
I have discovered from a user on the Apple Developer forums that this is a rare Xcode bug. By preventing the ascp process using Little Snitch Xcode will use an alternative upload method which works correctly.