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    <p>A brief perusal of <code>HtmlAgilityPack.HtmlWeb</code> confirms that it is using the synchronous <code>WebRequest</code> API. You are therefore placing long running tasks into the ThreadPool (via <code>Parallel</code>). The ThreadPool is designed for short-lived operations that yield the thread back to the pool quickly. Blocking on IO is a big no-no. Given the ThreadPool's reluctance to start new threads (because it is not designed for this kind of usage), you're going to be constrained by this behaviour. </p> <p>Fetch your web content asynchronously (<em>see <a href="http://msdn.microsoft.com/en-us/library/system.net.webrequest.begingetresponse.aspx" rel="noreferrer">here</a> and <a href="http://msdn.microsoft.com/en-us/library/system.io.stream.beginread.aspx" rel="noreferrer">here</a> for the correct API to use, you'll have to investigate further yourself...</em>) so that you are not tying up the ThreadPool with blocking tasks. You can then feed the decoded response to the HtmlAgilityPack for parsing.</p> <p>If you really want to jazz up performance, you'll also need to consider that WebRequest is incapable of performing asynchronous DNS lookup. IMO this is a terrible flaw in the design of WebRequest.</p> <blockquote> <p>The BeginGetResponse method requires some synchronous setup tasks to complete (DNS resolution, proxy detection, and TCP socket connection, for example) before this method becomes asynchronous. </p> </blockquote> <p>It makes high performance downloading a real PITA. It's at about this time that you might consider writing your own HTTP library so that everything can execute without blocking (and therefore starving the ThreadPool).</p> <p>As an aside, getting maximum throughput when chumming through web-pages is a tricky affair. In my experience, you get the code right and are then let down by the routing equipment it has to go through. Many domestic routers simply aren't up to the job.</p>
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    1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
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    1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
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    1. COThanks, how can I fetch my web content asynchronously? I have all my links pre-generated. Is this what you meant? So basically I have 1000s of links ready to be parsed so I can use the parsed info to further get the data I need like topic title, topic owner, date, etc, by parsing the data given to my by the html agility pack.
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    2. COThanks spender that makes sense.
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    3. COBtw I implemented the web response and passed it to html agility pack but the perf isn't that much better. The initial GetAllLinks is 2x faster, but others are still the same and still very low cpu usage (3%). Lastly do you know about `DownloadStringAsync`? Should I use this one instead of `DownloadString`?
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