Hi ,

We use oracle application server  and have some pausing problems inside
the java vm. The problem shows itself as pausings of executions , when
clients start to get late responses ( here lat e means < 4 sec. ) , i
see more than 10 garbage collector operations . The client applications
are web services and do database queries. The java process ( the os is
sun solaris) , according to the prstat  , has > 1000 threads inside ,
and during the garbage collectiong phase , consumes more than 60% cpu
time.  ( the server has 2 cpus - 2 gb. ram) The java process uses the
following parameters:

What i think is , the reason of the suspensions is garbage collector
activity.

In order to decrease the time that cause pausing , i either increase
the virtual memory allocated by the java process ,  or change the
garbage collector method.  Before adding up mor memory to teh system  ,
i want to be sure the effect of changing garbag ecollector methodology.

The gc used here is serial garbage collector , in order to speed it up
, the documents say that parallel garbage collector is used.

I write a small test program . This program creates 1000 threads  .
Each thread creates objects by using new  in a loop , and this causes
the garbage collector runs heavily in order to clean teh garbages.  And
i run the program bu using different garbage collectors but
unfortunately , i dont see great difference  beetween serial and
parallel gc ,and serial gc is faster.

Why does this so?

Serial gc:

timex java  -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
-Xmx450m -Xms450m  -XX:+PrintGCApplicationConcurrentTime
-XX:+PrintGCApplicationStoppedTime -XX:+UseSerialGC test > test1

real       23.48
user     3:26.67
sys         4.33

parallel gc:

timex java  -server -verbose:gc -XX:+PrintGCDetails
-XX:+PrintGCTimeStamps   -Xmx450m -Xms450m
-XX:+PrintGCApplicationConcurrentTime
-XX:+PrintGCApplicationStoppedTime -XX:+UseParallelGC test > test1

real       24.35
user     3:24.68
sys        30.95

and here is the test code:

(I run this test on a bigger box , 24gb.ram , 6 dual core solaris cpus
)

import java.util.*;
import java.net.*;
import java.io.*;

class testTh extends Thread
{
  public int val ;
 public testTh ( int pval) { val=pval; }
   public void run() {
      int i=0;
    String s  =new String("aaaa");
    boolean flag=true;
     while (flag)
    {
        for (int j=0;j<100000;j++) {
                  s = new String("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
        }
       i++;
       if (i>10) flag=false;
    }
    }
}

public class test
{
 public void dene() {
    for ( int j=0;j<1000;j++)
        (new testTh(j)).start();

      }
 public static void main(String args[])
  {
       test t = new test();
       t.dene();
}
}

Kind Regards,
hope