Full GC run freeing no memory despite many unreachable objects

Y. S. Ramakrishna y.s.ramakrishna at oracle.com
Wed Nov 10 10:03:56 PST 2010


Have you tried say doubling the size of your heap (old gen and
perm gen) to see what happens to the problem? May be you are using a
heap that is much too small for your application's natural footprint on
the platform on which you are running it? If you believe the process
heap needs should not be so large, check what the heap contains --
does a jmap -histo:live show many objects as live that you believe
should have been collected? Have you tried to determine, using a
tool such as jhat on these jmap heap dumps, to see if your application
has a real leak after all?

If you have determined that you do not have a leak, can you share
a test case? (Also please first try the latest 6u23 JDK before
you try to design a test case.)

best regards.
-- ramki


On 11/10/10 09:22, Darragh Curran wrote:
> Ooops, Here's the jstat output with headings:
> 
> S0C    S1C    S0U    S1U      EC       EU        OC         OU
> PC     PU    YGC     YGCT    FGC    FGCT     GCT
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060013.9
> 37376.0 37182.0  38654 1288.741 1105  5636.779 6925.520
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.0
> 37376.0 37182.0  38654 1288.741 1106  5646.857 6935.598
> ...
> ...
> ...
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1107  5656.903 6945.644
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1107  5656.903 6945.644
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
> 
> It looks like the perm gen is full (~99%)
> 
> The process doesn't recover on its own. Here's some other gc output
> from our logs:
> 
> 
> Heap
>  PSYoungGen      total 531712K, used 517887K [0x92d80000, 0xb42d0000,
> 0xb42d0000)
>   eden space 517888K, 99% used [0x92d80000,0xb273fff8,0xb2740000)
>   from space 13824K, 0% used [0xb2740000,0xb2740000,0xb34c0000)
>   to   space 14400K, 0% used [0xb34c0000,0xb34c0000,0xb42d0000)
>  PSOldGen        total 1092288K, used 1060042K [0x502d0000,
> 0x92d80000, 0x92d80000)
>   object space 1092288K, 97% used [0x502d0000,0x90e02a20,0x92d80000)
>  PSPermGen       total 37376K, used 37186K [0x4c2d0000, 0x4e750000, 0x502d0000)
>   object space 37376K, 99% used [0x4c2d0000,0x4e720b60,0x4e750000)
> 
> Nov 9, 2010 9:29:48 AM sun.rmi.transport.tcp.TCPTransport$AcceptLoop
> executeAcceptLoop
> WARNING: RMI TCP Accept-0: accept loop for
> ServerSocket[addr=0.0.0.0/0.0.0.0,port=0,localport=36857] throws
> java.lang.OutOfMemoryError: GC overhead limit exceeded
>         at sun.rmi.runtime.NewThreadAction.run(NewThreadAction.java:116)
>         at sun.rmi.runtime.NewThreadAction.run(NewThreadAction.java:34)
>         at java.security.AccessController.doPrivileged(Native Method)
>         at sun.rmi.transport.tcp.TCPTransport$1.newThread(TCPTransport.java:94)
>         at java.util.concurrent.ThreadPoolExecutor.addThread(ThreadPoolExecutor.java:672)
>         at java.util.concurrent.ThreadPoolExecutor.addIfUnderMaximumPoolSize(ThreadPoolExecutor.java:721)
>         at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:657)
>         at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:384)
>         at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:341)
>         at java.lang.Thread.run(Thread.java:619)
> 
>>From jmap I can see that most of the unreachable objects are
> LinkedHashMap.Entry objects that I know are created as part of many
> requests.
> 
> Darragh
> 
> On Wed, Nov 10, 2010 at 5:03 PM, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:
>>  I assume that the Java process does not recover on it's
>> own and has to be killed?
>>
>> What are the column heading for your jstat output?
>>
>> Turn on GC logging (if you don't already have it on) and check to
>> see if your perm gen is full.
>>
>> If your perm gen is not full but the Java heap appears to be
>> full, then the garbage collector just thinks that all that data
>> is live.  You used jmap.  Do you know what's filling up
>> the heap?
>>
>>
>>
>> On 11/10/2010 7:47 AM, Darragh Curran wrote:
>>> Hi,
>>>
>>> I hope someone can help me understand this better.
>>>
>>> I'm running java version "Java(TM) SE Runtime Environment (build
>>> 1.6.0_19-b04) Java HotSpot(TM) Server VM (build 16.2-b04, mixed mode)"
>>>
>>> It runs tomcat, with jvm heap options '-Xmx1600m -Xms1600m'
>>>
>>> Every few weeks a host becomes unavailable for requests. When I look
>>> into it, the java process is using 100% CPU, seems to have no running
>>> threads when I do multiple stack dumps, and based on jstat output
>>> appears to spend all it's time doing full gc runs:
>>>
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1107  5656.903 6945.644
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1108  5666.547 6955.287
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
>>> 14400.0 13824.0  0.0    0.0   517888.0 517888.0 1092288.0  1060014.1
>>> 37376.0 37182.0  38654 1288.741 1109  5675.945 6964.686
>>>
>>> I used jmap to dump the heap for analysis. When I analyse it I see
>>> that 94% of objects are unreachable, but not yet collected.
>>>
>>>> From jstat it appears that gc is running roughly every 10 seconds and
>>> lasting approx 10 seconds, but fails to free any memory.
>>>
>>> I'd really appreciate some advise on how to better understand my
>>> problem and what to do to try and fix it.
>>>
>>> Thanks,
>>> Darragh
>>> _______________________________________________
>>> hotspot-gc-use mailing list
>>> hotspot-gc-use at openjdk.java.net
>>> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
>> _______________________________________________
>> hotspot-gc-use mailing list
>> hotspot-gc-use at openjdk.java.net
>> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
>>
> _______________________________________________
> hotspot-gc-use mailing list
> hotspot-gc-use at openjdk.java.net
> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
_______________________________________________
hotspot-gc-use mailing list
hotspot-gc-use at openjdk.java.net
http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use


More information about the hotspot-gc-dev mailing list