Aggressive Heap and garbage collection in 1.4.2

Question

We are trying to monitor the memory usage and the garbage collection for one of our application servers. We are using JDK 1.4.2 b-19 on solaris 8. The machine has 4 900 Mhz CPUs and 8GB ram. The VM options are:
-server -XX:+AggressiveHeap -Xms3512m -Xmx3512m -verbose:gc
-XX:+PrintHeapAtGC -XX:+PrintTenuringDistribution -XX:+PrintGCTimestamps.The first full GC kicks in when the old generation gets full which is understandable. After that however, the full gc kicks in much more frequently and even the gc pauses are fairly long. Below are some of the output from gc.
For the first GC the old generation was almost full.
PSYoungGen total 1379840K, used 1324288K
PSOldGen total 2123648K, used 2103378K
For the second GC, young generation is 25MB out of 1300MB and old generation is 1100MB out of 2100MB. Still the full gc kicked in and took 23 secs.
PSYoungGen total 1356608K, used 25856K
PSOldGen total 2123648K, used 1169626K
I understand that the adaptive sizing is kicking in (by default) but it should make life better not worse. If the full GC could wait till the old generation gets full again, I will get lesser number of full gc pauses and few and far in between.
Any idea as to what I can do?
thanks
vinay
{Heap before GC invocations=108:
Heap
PSYoungGen      total 1379840K, used 1324288K [0x1a000000, 0x73e20000, 0x73e20000)
  eden space 228096K, 100% used [0x1a000000,0x27ec0000,0x27ec0000)
  from space 1151744K, 95% used [0x27ec0000,0x6ad40000,0x6e380000)
  to   space 92800K, 0% used [0x6e380000,0x6e380000,0x73e20000)
PSOldGen        total 2123648K, used 2103378K [0x73e20000, 0xf5800000, 0xf5800000)
  object space 2123648K, 99% used [0x73e20000,0xf4434af8,0xf5800000)
PSPermGen       total 31872K, used 31768K [0xf5800000, 0xf7720000, 0xf9800000)
  object space 31872K, 99% used [0xf5800000,0xf7706200,0xf7720000)
2842.142: [Full GC 3427666K->1083494K(3503488K), 26.6495189 secs]
Heap after GC invocations=108:
Heap
PSYoungGen      total 1379840K, used 0K [0x1a000000, 0x73e20000, 0x73e20000)
  eden space 1287040K, 0% used [0x1a000000,0x1a000000,0x688e0000)
  from space 92800K, 0% used [0x6e380000,0x6e380000,0x73e20000)
  to   space 92800K, 0% used [0x688e0000,0x688e0000,0x6e380000)
PSOldGen        total 2123648K, used 1083494K [0x73e20000, 0xf5800000, 0xf5800000)
  object space 2123648K, 51% used [0x73e20000,0xb6039978,0xf5800000)
PSPermGen       total 63744K, used 31768K [0xf5800000, 0xf9640000, 0xf9800000)
  object space 63744K, 49% used [0xf5800000,0xf7706200,0xf9640000)
{Heap before GC invocations=114:
Heap
PSYoungGen      total 1356608K, used 25856K [0x1a000000, 0x73e20000, 0x73e20000)
  eden space 1240576K, 0% used [0x1a000000,0x1a000000,0x65b80000)
  from space 116032K, 22% used [0x6ccd0000,0x6e610000,0x73e20000)
  to   space 116032K, 0% used [0x65b80000,0x65b80000,0x6ccd0000)
PSOldGen        total 2123648K, used 1169626K [0x73e20000, 0xf5800000, 0xf5800000)
  object space 2123648K, 55% used [0x73e20000,0xbb456858,0xf5800000)
PSPermGen       total 65536K, used 31773K [0xf5800000, 0xf9800000, 0xf9800000)
  object space 65536K, 48% used [0xf5800000,0xf7707578,0xf9800000)
3153.022: [Full GC 1195482K->1149586K(3482688K), 23.3155823 secs]
Heap after GC invocations=114:
Heap
PSYoungGen      total 1359040K, used 0K [0x1a000000, 0x73e20000, 0x73e20000)
  eden space 1245440K, 0% used [0x1a000000,0x1a000000,0x66040000)
  from space 113600K, 0% used [0x6cf30000,0x6cf30000,0x73e20000)
  to   space 113600K, 0% used [0x66040000,0x66040000,0x6cf30000)
PSOldGen        total 2123648K, used 1149586K [0x73e20000, 0xf5800000, 0xf5800000)
  object space 2123648K, 54% used [0x73e20000,0xba0c4830,0xf5800000)
PSPermGen       total 65536K, used 31773K [0xf5800000, 0xf9800000, 0xf9800000)
  object space 65536K, 48% used [0xf5800000,0xf7707578,0xf9800000)
}

Answer 1

We also had similar issues...If you are using RMI it might cause Full GC. This is the snippet from http://java.sun.com/docs/hotspot/gc/
<snip>
Garbage can't be collected in these distributed applications without occasional local collection, so RMI forces periodic full collection. The frequency of these collections can be controlled with properties. For example,
java -Dsun.rmi.dgc.client.gcInterval=3600000
-Dsun.rmi.dgc.server.gcInterval=3600000
</snip>
By default this is 1 min. So try changing this and try it out.