reasons why GcTimeLimit might not be erroring out?

Question

I have a web service in Java, contained in Jetty. I'm using Sun's Java 6 with the default ParallelGC, and I have the following command-line options turned on: "-verbose:gc -XX:+PrintGCTimeStamps --XX:+PrintGCDetails".

When my process is out of memory, I see loglines like this, back-to-back:

66872.846: [Full GC [PSYoungGen: 932534K->930686K(1865088K)] [PSOldGen: 5595037K->5595024K(5595136K)] 6527571K->6525710K(7460224K) [PSPermGen: 16488K->16487K(21504K)], 12.2488150 secs] [Times: user=12.25 sys=0.00, real=12.24 secs] 
66885.098: [Full GC [PSYoungGen: 932608K->932608K(1865088K)] [PSOldGen: 5595024K->5595024K(5595136K)] 6527632K->6527632K(7460224K) [PSPermGen: 16487K->16487K(21504K)], 9.6745600 secs] [Times: user=9.66 sys=0.01, real=9.67 secs] 
66894.773: [Full GC [PSYoungGen: 932608K->932488K(1865088K)] [PSOldGen: 5595024K->5595023K(5595136K)] 6527632K->6527512K(7460224K) [PSPermGen: 16487K->16487K(21504K)], 11.8445420 secs] [Times: user=11.85 sys=0.00, real=11.85 secs] 
66906.623: [Full GC [PSYoungGen: 932608K->932608K(1865088K)] [PSOldGen: 5595023K->5595023K(5595136K)] 6527631K->6527631K(7460224K) [PSPermGen: 16487K->16487K(21504K)], 9.6006950 secs] [Times: user=9.60 sys=0.00, real=9.60 secs] 
66916.224: [Full GC [PSYoungGen: 932608K->932488K(1865088K)] [PSOldGen: 5595023K->5595023K(5595136K)] 6527631K->6527512K(7460224K) [PSPermGen: 16487K->16487K(21504K)], 9.6498320 secs] [Times: user=9.65 sys=0.00, real=9.65 secs] 
66925.881: [Full GC [PSYoungGen: 932608K->0K(1865088K)] [PSOldGen: 5595023K->4133351K(5595136K)] 6527631K->4133351K(7460224K) [PSPermGen: 16487K->16487K(21504K)], 6.8990990 secs] [Times: user=6.90 sys=0.00, real=6.90 secs] 

The first five lines appear to show the garbage collector completely failing to make any progress. According to my understanding of the JVM, this should result in an OutOfMemoryError, but I don't see anything like that in the logs. Is it possible that something (at the JVM level) is preventing them from being thrown? Or maybe either Jetty or my application is suppressing them?

Thanks for your advice!

Answer 1

Try explicitly setting the option, or setting -XX:GCHeapFreeLimit instead. The documentation for these options is pretty thin, and may not exactly reflect the behavior of the JVM you are running. (Or maybe the defaults for relevant options have changed.)