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POPerformance Linq
 

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  1. POPerformance Linq
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    <p>Today I tested the performance impacts of Linq and PLinq querys. Therefore I used the article on <a href="http://msdn.microsoft.com/en-gb/library/dd554944.aspx" rel="nofollow">msdn How to: Measure PLINQ Query Performance</a>. </p> <pre><code>void Main() { var source = Enumerable.Range(0, 600000000); System.Diagnostics.Stopwatch sw; var queryToMeasure1 = from num in source where num % 3 == 0 select Math.Sqrt(num); var queryToMeasure2 = from num in source.AsParallel() where num % 3 == 0 select Math.Sqrt(num); long freq = Stopwatch.Frequency; Console.WriteLine("Timer frequency in ticks per second = {0}", freq); Console.WriteLine("Measuring 1"); sw = System.Diagnostics.Stopwatch.StartNew(); foreach (var n in queryToMeasure1) { } Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds); Console.WriteLine("Measuring 2"); sw = System.Diagnostics.Stopwatch.StartNew(); foreach (var n in queryToMeasure2) { } Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds); Console.WriteLine("Measuring 3"); sw = System.Diagnostics.Stopwatch.StartNew(); System.Threading.Tasks.Parallel.ForEach(queryToMeasure1, n =&gt; {}); Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds); Console.WriteLine("Measuring 4"); sw = System.Diagnostics.Stopwatch.StartNew(); System.Threading.Tasks.Parallel.ForEach(queryToMeasure2, n =&gt; {}); Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds); Console.WriteLine("Measuring 5"); sw = System.Diagnostics.Stopwatch.StartNew(); queryToMeasure2.ForAll(n =&gt; {}); Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds);); } </code></pre> <p>Test environment: LinqPad4 on Win7 Enterprise, 64bit, 8GB RAM, I7-2600 (8cores)</p> <p>I figured out, and can't explain, why the query on one core (Measurement 1) are faster than the paralleled queries. Do I have to add more select delegates to get benefit from paralleled tasks?</p> <p>But now the results:</p> <p>1.Run: with an enumerable range of 60000:</p> <pre><code>Timer frequency in ticks per second = 3312851 Measuring 1 Total ticks: 3525 - Elapsed time: 1 ms Measuring 2 Total ticks: 15802 - Elapsed time: 4 ms Measuring 3 Total ticks: 5940 - Elapsed time: 1 ms Measuring 4 Total ticks: 26862 - Elapsed time: 8 ms Measuring 5 Total ticks: 4387 - Elapsed time: 1 ms </code></pre> <p>2.Run: with an enumerable range of 600000000:</p> <pre><code>Timer frequency in ticks per second = 3312851 Measuring 1 Total ticks: 29740243 - Elapsed time: 8977 ms Measuring 2 Total ticks: 33722438 - Elapsed time: 10179 ms Measuring 3 Total ticks: 77145502 - Elapsed time: 23286 ms Measuring 4 Total ticks: 120078284 - Elapsed time: 36246 ms Measuring 5 Total ticks: 30899585 - Elapsed time: 9327 ms </code></pre> <p>Interesting fact: using the Garbage Collector before performing the test script will increase the time for Measurement 4 vastly:</p> <p>3.Run: with an enumerable range of 600000000 and Garbage Collector (from LinqPad):</p> <pre><code>Timer frequency in ticks per second = 3312851 Measuring 1 Total ticks: 29597830 - Elapsed time: 8934 ms Measuring 2 Total ticks: 33532083 - Elapsed time: 10121 ms Measuring 3 Total ticks: 76403692 - Elapsed time: 23062 ms Measuring 4 Total ticks: 58534548 - Elapsed time: 17668 ms Measuring 5 Total ticks: 32943622 - Elapsed time: 9944 ms </code></pre> <p>In conclusion, can I say that method 1 is the most suitable option to perform small select queries and method 5 when the select delegates will increase? </p>
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    1. COModulo and `Math.Sqrt` are not good candidates for PLINQ since they are trivial(too fast). The more expensive the better. http://msdn.microsoft.com/en-us/library/dd997399.aspx You might also want to have a look at [my question here](http://stackoverflow.com/questions/7582591/how-to-plinq-an-existing-linq-query-with-joins), i've listed some recommendable readings.
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    2. CODo you have some actual question? Or did you just want to start a discussion? If that's the case, then your “question” is not appropriate for SO.
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    3. CONo I don't want to start a discussion, just want to know which is the best method to do some huge work. And was not quite sure if the delegates were to cheap to make a qualified statement. According to msdn it was. According to the guys over here, it's not
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