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From Leon Rosenberg <rosenberg.l...@gmail.com>
Subject Re: What is the healthy interval length for young gc?
Date Mon, 03 Jan 2011 14:41:23 GMT
On Mon, Jan 3, 2011 at 3:10 PM, Pid <pid@pidster.com> wrote:
> On 1/3/11 1:10 PM, Leon Rosenberg wrote:
>> Actually no, in my understanding both are independent. I mean the gc
>> doesn't start "to copy over" if young is full, it simply cleans young.
>> However,
>> to quote your article: "Old generation objects are objects that
>> survived a few collections in the young generation area", and if
>> objects managed to survive longer as they should in the young space,
>> they might have been copied to old gen, despite the fact, that they
>> are young generation objects by nature (meaning short lifetime). This
>> theory is what I'm trying to check.
>
> Objects which survive collections in young generations will make their
> way into the old generation, and then sit around for a long time waiting
> to be collected.

Hello pid-ster,


>
> What are your memory settings currently and how are the generations divided?

-Xmx12G
-Xms12G
-XX:PermSize=128M
-XX:MaxPermSize=256M
-XX:+DisableExplicitGC
-verbose:GC
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-Xloggc:/.../tomcat/logs/gc_tomcat.log

jmap says:

Attaching to process ID 16969, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 14.2-b01

using thread-local object allocation.
Parallel GC with 6 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 12884901888 (12288.0MB)
   NewSize          = 2686976 (2.5625MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 134217728 (128.0MB)
   MaxPermSize      = 268435456 (256.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 4074897408 (3886.125MB)
   used     = 1509410704 (1439.4862213134766MB)
   free     = 2565486704 (2446.6387786865234MB)
   37.04168603206219% used
>From Space:
   capacity = 110755840 (105.625MB)
   used     = 47330080 (45.137481689453125MB)
   free     = 63425760 (60.487518310546875MB)
   42.73371047522189% used
To Space:
   capacity = 109314048 (104.25MB)
   used     = 0 (0.0MB)
   free     = 109314048 (104.25MB)
   0.0% used
PS Old Generation
   capacity = 8589934592 (8192.0MB)
   used     = 6636110912 (6328.688537597656MB)
   free     = 1953823680 (1863.3114624023438MB)
   77.25449874997139% used
PS Perm Generation
   capacity = 268435456 (256.0MB)
   used     = 228667664 (218.07447814941406MB)
   free     = 39767792 (37.92552185058594MB)
   85.18534302711487% used



>
> How many processors do you have available and are you using CMS &
> incremental mode?

vm with 6 assigned cores and no to both.


I also might add, that the amount of free space right now is much
higher as during the peak times, when its usually below 1GB (more
sessions, more caches).

regards
Leon

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