Getting results in order from multiple threads

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Hi, my requirement is to brake the MySQL database query into parts and execute each part within different threads for example

if user want to see the record from 1 to 1000 then query would be (Select * from record where rec_no > = 1 and rec_no <= 1000). Now instead of running this query I want to run 4 queries such as

1st query= (Select * from Record where rec_no > = 1 and rec_no <= 250)
2nd query = (Select * from Record where rec_no > = 251 and rec_no <= 500)
3rd query =(Select * from Record where rec_no > = 501 and rec_no <= 750)
4th query =Select * from Record where rec_no > = 751 and rec_no <= 1000)

this way all queries would take fraction of second and get executed parallel and fast.
I am getting result from all query but only facing problem to accumulate them in single array which would hold the result and reason behind that any thread would get executed first and return me the result.

part of my code is

C#

private void btnStartThread_Click(object sender, System.EventArgs e)
		{
            Thread[] m_WorkerThread = new Thread[Environment.ProcessorCount];
			

	  // create worker thread instance
            for (int i = 0; i < Environment.ProcessorCount; i++)
            {
                m_WorkerThread[i] = new Thread(WorkerThreadFunction));

                m_WorkerThread[i].Name = "Worker Thread Sample" + i;	

                m_WorkerThread[i].Start("querylist[i]");
            }
		}

C#

private void WorkerThreadFunction( string s)
		{
            //Thread[] t = new Thread[Environment.ProcessorCount];
            
                MyDefinedClass IClass;

                lClass = new MyDefineClass();

                Iclass.Run(s);
            
		}

finally I am getting result in

C#

private void AddString(array[] s)
		{
			
       final_array // would add record one by one, that is result of query 1, then query 2 
                   // till query 4 in order. but I am not aware of thread that is returning me           //result as any thread can return result first                  	
		}

Thanks in advance

Posted 22-Oct-13 6:38am

rameshKumar1717

Updated 22-Oct-13 6:39am

v4

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Dave Kreskowiak · Answer 1 · 2013-10-22T06:49:00

I see a ton of incorrect assumptions with this...

First, unless each of those threads is creating it's own connection to the database (which is time consuming), your queries, though in separate threads, are being sent and executed one at a time. A MySQL connection will only work on one query at a time.

Second, threads will execute in any order and at any time. You cannot get them to return results in a predetermined order. What you do to compensate for this is to add all the records to your collection, then sort the end result (which is time consuming).

Now, is your MySQL server running on the same machine as your code?? Putting together 4 threads isn't going to do anything at all since the MySQL server is going to be competing for CPU time with, not only your threads, but the hundreds of other threads on the system that are running.

I don't see how you're going to get a performance boost by threading when you have to pay for that boost with more time to assemble and clean up your query.