top查看java占用的内存比较多

top - :: up  days, :,   user,  load average: 0.03, 0.05, 0.05

Tasks:  total,    running,  sleeping,    stopped,    zombie

%Cpu(s):  0.0 us,  1.3 sy,  0.0 ni, 98.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st

KiB Mem :   total,    free,   used,   buff/cache

KiB Swap:   total,   free,   used.   avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND

  root           .598g   S   0.0 20.5  :01.18 jsvc

 root           .323g   S   0.0 17.0   :32.59 jsvc

 root           .136g   S   0.0 14.6 :06.62 jsvc

 root              S   0.0  9.2 :19.24 jsvc

可见每个占用了大概20%，还是比较高的，因为要部署新的服务，腾内存了

使用jstack查看一下进程的状态，其实也没什么用，不过我昨天刚学的java GC，就试用一下

jstack -F

Attaching to process ID , please wait...

Debugger attached successfully.

Server compiler detected.

JVM version is 25.111-b14

Deadlock Detection:

No deadlocks found.

Thread : (state = BLOCKED)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Interpreted frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Interpreted frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Interpreted frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

Thread : (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci= (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=, line= (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() @bci=, line= (Interpreted frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=, line= (Compiled frame)

 - java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=, line= (Interpreted frame)

 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=, line= (Interpreted frame)

 - java.lang.Thread.run() @bci=, line= (Interpreted frame)

后边不贴了，总之就是有大量的BLOCKED，这个程序说是bug导致的，下一个版本会修正，另外其他的进程实在IN_NATIVE状态，因为JAVA底层其实是C语言实现的，这个就是在执行C语言的调用，native

我竟然还以为是inactive，Naive

使用jstat分析一下gc，命令格式jstat -gc -t <PID>

jstat -gc -t

Timestamp        S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT

       484036.7 2048.0 2048.0  0.0   1296.0 694784.0 234952.5 1398272.0   259033.6  59136.0 57496.9 6400.0 6017.4      10.073         0.254   10.327

这里面S0C和S1C是两个survivor的容量，S0U和S1U是两个survivor已经使用的容量，EC和EU分别是新生代容量和已用容量，OC和OU是老年代的容量和已用，MC和MU是方法区的容量和使用大小，CCSC和CCSU是压缩类空间容量和使用大小，YGC是minor GC的次数，YGCT是minorGC的总计时间，FGC是major GC的次数，FGCT是major GC的时间，GCT是总共GC的占用时间。

其实这里还可以获取一下内存快照的，方法是

jmap -dump:format=b,file=heap.bin <pid>
file：保存路径及文件名
pid：进程编号（windows通过任务管理器查看，linux通过ps aux查看）

分析工具从http://www.eclipse.org/mat/下载，可惜我这里没有，所以说就算了吧

言归正传，用jmap分析下总的heap，heap就是堆，这里说下，堆和栈是有区别的，堆是存储变量，栈存储的是命令。堆是可以由应用程序来修改和申请空间，栈是由系统来管理的

root@localhost:~# jmap -heap

Attaching to process ID , please wait...

Debugger attached successfully.

Server compiler detected.

JVM version is 25.111-b14

using thread-local object allocation.

Parallel GC with  thread(s)

Heap Configuration:

   MinHeapFreeRatio         =

   MaxHeapFreeRatio         =

   MaxHeapSize              =  (.0MB)

   NewSize                  =  (.5MB)

   MaxNewSize               =  (.5MB)

   OldSize                  =  (.5MB)

   NewRatio                 =

   SurvivorRatio            =

   MetaspaceSize            =  (.796875MB)

   CompressedClassSpaceSize =  (.0MB)

   MaxMetaspaceSize         =  MB

   G1HeapRegionSize         =  (.0MB)

Heap Usage:

PS Young Generation

Eden Space:

   capacity =  (.5MB)

   used     =  (.6439056396484MB)

   free     =  (.856094360351562MB)

   96.33661100068511% used

From Space:

   capacity =  (.0MB)

   used     =  (.001068115234375MB)

   free     =  (.998931884765625MB)

   50.05340576171875% used

To Space:

   capacity =  (.0MB)

   used     =  (.0MB)

   free     =  (.0MB)

   0.0% used

PS Old Generation

   capacity =  (.5MB)

   used     =  (.53402709960938MB)

   free     =  (.9659729003906MB)

   18.493887008393216% used

震惊！运维工程师用jmap分析jvm，竟然……

Eden看起来有点高了，但是其实这么说也是不公平的，Eden（伊甸园）区满了就会触发minorGC，把不活跃的对象清理掉，几次GC后还没有被清理掉的进入survivor，还能幸存的进入老年代，所以如果一个进程说Linux的哪一块内存没有去过，其实潜台词就是他老了(逃

不过Eden还是不能太小了，否则如果被活跃的对象占满了，GC不会处理这些对象，新的对象一直等着进不来，就会造成进程假死了，参考文献

http://www.cnblogs.com/jackchen001/p/6902909.html

或者温和一点，大量的对象放进老生代，导致频繁的full GC，full GC是要暂停程序的，并且会占用大量的CPU，导致性能下降

http://blog.csdn.net/hengyunabc/article/details/24924843

现在就比较简单了，使用java -XX就可以调整了

这里可以看到NewRatio是2，那么就是NewGeneration:OldGeneration = 1:2，new占了1/3的空间，old占了2/3,这里调整一下，把总体从原来的2G调整到1G就可以了，这样老年代空间和新生代空间都缩小了一半，YGC会频繁一点，但是YGC很快，不太会影响，只要老年区不被沾满就行，如果还不放心可以把新生代调大一点，SUN官方推荐新生代为整体的3/8。SurvivoRatio是连个Survivor区与Eden区的大小比值，8就是Eden:Survivor=8:2

java -Xmx1024m -Xmn374m

这样调整后感觉好多了

参考文献

http://www.cnblogs.com/redcreen/archive/2011/05/04/2037057.html

http://www.importnew.com/1993.html

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