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POwhy increment of newFixedThreadPool result in poor performance?
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  1. POwhy increment of newFixedThreadPool result in poor performance?
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    copied!<p>I'm trying to change the execution of a report and have it done in concurrency. In a 'serail mode' the execution test takes 30 seconds and when using a concurrent mode I get 27 seconds (consider that few steps must be taken in serial I'm ok with the result). </p> <p>The thing that I still don't get is this line:</p> <pre><code>ExecutorService executor = Executors.newFixedThreadPool(4); </code></pre> <p>My computer is armed with 2x2.6 Ghz Quad Core and I would expect that the execution time will decrease if the newFixedThreadPool is high (16). In reality, the more I increase the newFixedThreadPool the slower the execution. This begs the question: What am I doing wrong or what am I failing to understand?!?!</p> <p>I'm embedding 2 results screenshots from my execution.</p> <p>A. newSingleThreadExecuter - runs in 23 sec</p> <p>B. newFixedThreadPool(4) - runs in 43 sec.</p> <p>Each time I submit a 'Worker' I get system.out the currentTimeMillis and the "fatched tkt" result is milliseconds that it takes to get the data from the db. (in strategy A - it takes ~3ms and in B up to 7ms).</p> <pre><code> Stopper stopper = new Stopper(); for (Long iNum : multimap.asMap().keySet()) { List&lt;Long&gt; tickets = (List&lt;Long&gt;) multimap.get(iNum); for (Long ticketNumber : tickets) { pojoPks = getPkData(iNum); Callable&lt;PojoTicket&gt; worker = new MaxCommThread(ticketNumber, pojoPks); Future&lt;PojoTicket&gt; submit = executor.submit(worker); futures.add(submit); } } System.out.println("futurues: " +futures.size()); for (Future&lt;PojoTicket&gt; future : futures) { try { PojoTicket pojoTicket = future.get(); //do the rest here } catch (InterruptedException e) { System.out.println("----------------------&gt;InterruptedException"); } catch (ExecutionException e) { System.out.println("----------------------&gt;ExecutionException"); } } executor.shutdown(); stopper.stop(); </code></pre> <p><img src="https://i.stack.imgur.com/nqUwN.png" alt="enter image description here"></p> <p><img src="https://i.stack.imgur.com/I3iXH.png" alt="enter image description here"></p>
 

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