Re: java

On 17.12.2006 12:14, hopehope_123 wrote:
> 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:

2GB for a Solaris box seems a bit low - especially if it has to handle traffic from 1000 clients concurrently.

> 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 stops all other threads and does only GC - this is more efficient than parallel GC - you can find articles about this on java.sun.com - I don't have a link handy.

Parallel GC is overall slower but has smaller stop the world phases which leads to better responsiveness.

> 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

Note that there is a whole bunch of other GC parameters that affect performance. You can for example change the ration between young and old generation heap space etc.

        robert Received on Sun Dec 17 2006 - 05:31:21 CST