ParOldGen, old gen full, frequent full gc instead of heap expansion

[Ion Savin]

Hi,

I'm using -Xms512m -Xmx2200m -Xmn400m and for some reason even if the old generation is (almost?) full the jvm doesn't grow the heap size above the -Xms value (and with it the old generation size) and instead it does frequent full GCs.

Looking at the heap occupancy after the full gc it seems that the total heap free space is at 32% which is below the 40% default for -XX:MinHeapFreeRatio at which the heap should expand.

Can anyone help me understand why the jvm is behaving this way? Does it have anything to do with the disabled adaptive sizing?

There is no OOM exception and the application works OK (except for the total 1000+ seconds duration).

[...] (last minor and first major gc)

2012-09-12T08:47:23.733+0900: 26502.170: [GC [PSYoungGen: 257277K->40945K(307200K)] 353828K->149380K(421888K), 0.0422890 secs] [Times: user=0.40 sys=0.01, real=0.04 secs] 
2012-09-12T08:47:23.775+0900: 26502.213: [Full GC [PSYoungGen: 40945K->7139K(307200K)] [ParOldGen: 108434K->114683K(114688K)] 149380K->121823K(421888K) [PSPermGen: 10684K->10663K(21888K)], 0.7935330 secs] [Times: user=5.90 sys=0.07, real=0.79 secs]

[...] (~2900 full gcs between these two and no minor gc)

2012-09-12T19:36:08.332+0900: 65426.770: [Full GC [PSYoungGen: 204800K->169466K(307200K)] [ParOldGen: 114687K->114687K(114688K)] 319487K->284154K(421888K) [PSPermGen: 10763K->10763K(21248K)], 0.2298050 secs] [Times: user=2.02 sys=0.00, real=0.23 secs]

* jvm version:

java version "1.6.0_31"
Java(TM) SE Runtime Environment (build 1.6.0_31-b04)
Java HotSpot(TM) 64-Bit Server VM (build 20.6-b01, mixed mode)

* cmdline flags:

-XX:InitialHeapSize=536870912 -XX:MaxHeapSize=2306867200 -XX:MaxNewSize=419430400 -XX:NewSize=419430400 -XX:ParallelGCThreads=13 -XX:+PrintCommandLineFlags -XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintTenuringDistribution -XX:SurvivorRatio=2 -XX:+TraceClassUnloading -XX:-UseAdaptiveSizePolicy -XX:+UseCompressedOops -XX:+UseParallelGC -XX:+UseParallelOldGC

* jmap -heap output:
using thread-local object allocation.
Parallel GC with 13 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 2306867200 (2200.0MB)
   NewSize          = 419430400 (400.0MB)
   MaxNewSize       = 419430400 (400.0MB)
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 2
   PermSize         = 21757952 (20.75MB)
   MaxPermSize      = 85983232 (82.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 209715200 (200.0MB)
   used     = 198097304 (188.9203109741211MB)
   free     = 11617896 (11.079689025878906MB)
   94.46015548706055% used
>From Space:
   capacity = 104857600 (100.0MB)
   used     = 0 (0.0MB)
   free     = 104857600 (100.0MB)
   0.0% used
To Space:
   capacity = 104857600 (100.0MB)
   used     = 0 (0.0MB)
   free     = 104857600 (100.0MB)
   0.0% used
PS Old Generation
   capacity = 117440512 (112.0MB)
   used     = 117437840 (111.99745178222656MB)
   free     = 2672 (0.0025482177734375MB)
   99.99772480555943% used
PS Perm Generation
   capacity = 21757952 (20.75MB)
   used     = 11023832 (10.513145446777344MB)
   free     = 10734120 (10.236854553222656MB)
   50.6657611892884% used

Regards,
 Ion Savin