Databases
StackOverflow2013
Postsdbo
POHow to get max performance using Parallel.For/ForEach? (performance timings included)
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
    primarykey
    data
    text
    <p>I am trying to parallelize my web parsing tool but the speed gains seem very minimal. I have i7-2600K (8 cores hyper-threading).</p> <p>Here is some code to show you the idea. I only show <code>Parallel.ForEach</code> but you get the idea:</p> <pre><code>List&lt;string&gt; AllLinks = this.GetAllLinks(); ConcurrentDictionary&lt;string, Topic&gt; AllTopics = new ConcurrentDictionary&lt;string, Topic&gt; ( ); int count = 0; Stopwatch sw = new Stopwatch ( ); sw.Start ( ); Parallel.ForEach ( AllLinks, currentLink =&gt; { Topic topic = this.ExtractTopicData ( currentLink ); this.AllTopics.TryAdd ( currentLink, topic ); ++count; if ( count &gt; 50 ) { Console.WriteLine ( sw.ElapsedMilliseconds ); count = 0; } } ); </code></pre> <p>I get these timings:</p> <pre><code>Standard foreach loop: 24582 59234 82800 117786 140315 2 links per second Paralel.For: 21902 31649 41168 49817 59321 5 links per second Paralel.ForEach: 10217 20401 39056 49220 58125 5 links per second </code></pre> <p>Firstly why is the "startup" timing is much slower in <code>Parallel.For</code>?</p> <p>Other than that the parallel loops give me 2.5x speed over the standard foreach loop. Is this normal?</p> <p>Is there a setting I can set so that the parallel loops can use all the cores?</p> <p>EDIT:</p> <p>Here is pretty much what <code>ExtractTopicData</code> does:</p> <pre><code>HtmlAgilityPack.HtmlWeb web = new HtmlWeb ( ); HtmlAgilityPack.HtmlDocument doc = web.Load ( url ); IEnumerable&lt;HtmlNode&gt; links = doc.DocumentNode.SelectNodes ( "//*[@id=\"topicDetails\"]" ); var topic = new Topic(); foreach ( var link in links ) { //parse the link data } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USJoan Venge
    1. USJoan Venge
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
      1. USJoan Venge
      1. VTFavorite
    3. VO
      singulars
      1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhat exactly does this.ExtractTopicData do. WebRequests? Which API?
      singulars
      1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
      1. USspender
    2. COSorry forgot to mention, it uses the html agility pack and does some parsing. Added details above.
      singulars
      1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
      1. USJoan Venge
    3. COAlso, you are mutating a local variable (count) in a non-safe manner. That will be unreliable.
      singulars
      1. POHow to get max performance using Parallel.For/ForEach? (performance timings included)
      1. USJudah Himango
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload