Re: GC issues

(I just today glanced through my adv-java archives and saw this.)

Couple of questions come to mind:
(*) The fact that you're getting Full GC sweeps one right after the other
clearly indicates you're maxed out. Do you have a leak somewhere? What's the
memory curve look like over that hour's time? (JConsole can be your friend
here.)
(*) Notice how your GC reporting numbers aren’t changing one bit? It looks
like the JVM is doing a full sweep, then can't find anything to free
up--that's a second smell that indicates a leak in your code someplace. Use
the MemoryPool MBeans (available through JConsole), take a snapshot of the
heap, and have a look at it in jhat. (Or, if you prefer, substitute your
favorite commercial profiler's functionality here. Either way, you need a
better look inside the heap.)
(*) What platform are you running on? If you're on a 32-bit operating
system, then specifying -mx4096M is a terrible idea, because you're
essentially giving the JVM carte blanche to try and allocate a Java heap
that's 4GB in size, which can never happen in a 32-bit (4GB) process! I'm
guessing you're on a 64-bit platform, since according to your GC output here
the heap itself thinks it's 5GB in size, but I figured I'd ask anyway.

Ted Neward
Java, .NET, XML Services
Consulting, Teaching, Speaking, Writing
http://www.tedneward.com
 

> -----Original Message-----
> From: Discussion of advanced Java topics. [mailto:ADVANCED-
> [email protected]] On Behalf Of Avinash Lakshman
> Sent: Monday, October 01, 2007 8:22 PM
> To: [email protected]
> Subject: [ADVANCED-JAVA] GC issues
> 
> Hi All
> 
> We are trying to profile our software on a single server in order to
> determine how many transactions per second it can handle. We were
> trying to
> figure out to what extent we can push it to. What we are observing is
> that
> things run fine on the server for like an hour and then everything goes
> haywire. We tried to dump the GC details and figured that the full
> times are
> on an average 15 secs (snapshot shown below). I am using the following
> VM
> options
> -Xms1024M -Xmx4096M -XX:+UseConcMarkSweepGC
> -XX:CMSInitiatingOccupancyFraction=50. How do I go about tuning this? I
> am
> sure one of you might have more insight and point in the right
> direction as
> to what the next steps should be for me. Please advice
> 
> 
> GC details snapshot:
> 
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 14.9602090 secs]
> 5044415K->5044415K(5044416K), [Perm : 14286K->14286K(21248K)],
> 14.9604460 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 14.9600190 secs]
> 5044415K->5044415K(5044416K), [Perm : 14286K->14286K(21248K)],
> 14.9602830 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 14.9943380 secs]
> 5044415K->5044415K(5044416K), [Perm : 14286K->14286K(21248K)],
> 14.9946070 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 15.0132030 secs]
> 5044415K->5044415K(5044416K), [Perm : 14286K->14286K(21248K)],
> 15.0135150 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 15.0087010 secs]
> 5044415K->5044415K(5044416K), [Perm : 14286K->14286K(21248K)],
> 15.0089700 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 15.0059100 secs]
> 5044415K->5044282K(5044416K), [Perm : 14286K->14286K(21248K)],
> 15.0062270 secs]
> 
> Exception in thread "ROW-MUTATION:7" java.lang.OutOfMemoryError: Java
> heap space
> 
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 15.0145700 secs]
> 5044415K->5044308K(5044416K), [Perm : 14286K->14286K(21248K)],
> 15.0148770 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 15.0113510 secs]
> 5044415K->5044330K(5044416K), [Perm : 14286K->14286K(21248K)],
> 15.0116270 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 15.0235560 secs]
> 5044415K->5044354K(5044416K), [Perm : 14286K->14286K(21248K)],
> 15.0238610 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 18.5820490 secs]
> 5044415K->5044372K(5044416K), [Perm : 14286K->14286K(21248K)],
> 18.5823870 secs]
> [Full GC [Tenured: 3478911K->3478911K(3478912K), 14.9996820 secs]
> 5044415K->5044393K(5044416K), [Perm : 14286K->14286K(21248K)],
> 14.9999700 secs]
> 
> Thanks
> A
> 
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