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如何在eclipse dump Java内存占用情况和打印GC LOG
当使用java开发应用程序发生内存泄露的时候，经常会需要dump内存，然后使用内存分析工具，比如Eclipse Memory Analyzer(一般称作MAT)工具。
本文将介绍如何在eclipse中dump　内存。
提前准备：
　　一、下载ＭＡＴ　：　
二、测试代码如下：
package com.memoryLeakA
import java.util.ArrayL
import java.util.L
public class MemoryLeakDemo {
public static void main(String[] args) {
List&String& list = new ArrayList&String&();
while (true) {
list.add("OutOfMemoryError soon");
右键选择 run configurations
找到Arguments -----&VM arguments
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=c:/memoryLeakDemo.hprof-XX:+PrintGCDetails -XX:+PrintGCDateStamps
-XX:+PrintGCApplicationConcurrentTime
-XX:+PrintGCApplicationStoppedTime
-Xloggc:c:/memoryLeakDemoGc.log
点击Run运行。即可出现内存dump现象：
在c:/test目录下会出现两个文件：
其中memoryLeakDemo.hprof为dump的内存情况。
memoryleakDemoGc.log为打印的jvm gc 垃圾回收情况
使用Eclipse Memory Analyzer（MAT)打开memoryLeakDemo.hprof
，即可看到可疑的内存泄露情况，如下图：
打开memoryleakDemoGc.log日志：
出现类似于下图情况，可根据日志分析垃圾回收情况，从而分析JVM 内存使用情况。关于GC日志如何分析，请google之，将来会写文章介绍。
Application time: 0.0072104 seconds
T18:08:09.518+: [GC 0.079: [DefNew: 4017K-&261K(4928K), 0.0020189 secs] 4017K-&K), 0.0020804 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
Total time for which application threads were stopped: 0.0118427 seconds
Application time: 0.0015514 seconds
T18:08:09.531+: [GC 0.092: [DefNew: 2095K-&0K(4928K), 0.0022178 secs] 3258K-&K), 0.0022986 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Total time for which application threads were stopped: 0.0023873 seconds
Application time: 0.0021970 seconds
T18:08:09.536+: [GC 0.097: [DefNew: 2618K-&0K(4928K), 0.0027436 secs] 5788K-&K), 0.0027797 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Total time for which application threads were stopped: 0.0029137 seconds
Application time: 0.0033047 seconds
T18:08:09.542+: [GC 0.103: [DefNew: 3927K-&0K(4928K), 0.0040692 secs]0.107: [Tenured: 9715K-&K), 0.0078907 secs] 9715K-&K), [Perm : 376K-&376K(12288K)], 0.0120529 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
Total time for which application threads were stopped: 0.0121337 seconds
Application time: 0.0051220 seconds
T18:08:09.559+: [GC 0.120: [DefNew: 0K-&0K(4992K), 0.0019689 secs]0.122: [Tenured: 10078K-&K), 0.0086661 secs] 10078K-&K), [Perm : 376K-&376K(12288K)], 0.0107276 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
Total time for which application threads were stopped: 0.0108428 seconds
Application time: 0.0088859 seconds
T18:08:09.579+: [GC 0.140: [DefNew: 0K-&0K(4992K), 0.0026499 secs]0.143: [Tenured: 14987K-&K), 0.0113583 secs] 14987K-&K), [Perm : 376K-&376K(12288K)], 0.0141102 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]
Total time for which application threads were stopped: 0.0142300 seconds
Application time: 0.0131855 seconds
T18:08:09.606+: [GC 0.167: [DefNew: 0K-&0K(8960K), 0.0041453 secs]0.172: [Tenured: 22350K-&1K), 0.0153709 secs] 22350K-&1K), [Perm : 376K-&376K(12288K)], 0.0196298 secs] [Times: user=0.01 sys=0.00, real=0.02 secs]
Total time for which application threads were stopped: 0.0197569 seconds
Application time: 0.0192821 seconds
T18:08:09.646+: [GC 0.207: [DefNew: 0K-&0K(14976K), 0.0057633 secs]0.212: [Tenured: 33395K-&2K), 0.0206766 secs] 33395K-&2K), [Perm : 376K-&376K(12288K)], 0.0265551 secs] [Times: user=0.03 sys=0.00, real=0.03 secs]
Total time for which application threads were stopped: 0.0266673 seconds
Application time: 0.0289176 seconds
T18:08:09.701+: [GC 0.262: [DefNew: 0K-&0K(23872K), 0.0086104 secs]0.271: [Tenured: 49962K-&3K), 0.0294036 secs] 49962K-&3K), [Perm : 376K-&376K(12288K)], 0.0380994 secs] [Times: user=0.03 sys=0.00, real=0.04 secs]
Total time for which application threads were stopped: 0.0382799 seconds
Application time: 0.0436154 seconds
T18:08:09.783+: [GC 0.344: [DefNew: 0K-&0K(23872K), 0.0131421 secs]0.357: [Tenured: 74812K-&4K), 0.0415558 secs] 74812K-&4K), [Perm : 376K-&376K(12288K)], 0.0548393 secs] [Times: user=0.05 sys=0.00, real=0.06 secs]
Total time for which application threads were stopped: 0.0550578 seconds
Application time: 0.0657430 seconds
T18:08:09.904+: [GC 0.465: [DefNew: 0K-&0K(43968K), 0.0198380 secs]0.485: [Tenured: 112088K-&6K), 0.0608105 secs] 112088K-&6K), [Perm : 376K-&376K(12288K)], 0.0807997 secs] [Times: user=0.08 sys=0.00, real=0.08 secs]
Total time for which application threads were stopped: 0.0809335 seconds
Application time: 0.0991039 seconds
T18:08:10.084+: [GC 0.645: [DefNew: 0K-&0K(74240K), 0.0293317 secs]0.674: [Tenured: 168002K-&4784K), 0.0895410 secs] 168002K-&9024K), [Perm : 376K-&376K(12288K)], 0.1189829 secs] [Times: user=0.12 sys=0.00, real=0.12
T18:08:10.203+: [Full GC 0.764: [Tenured: 100905K-&4784K), 0.0861601 secs] 100905K-&3440K), [Perm : 376K-&371K(12288K)], 0.0862167 secs] [Times: user=0.08 sys=0.00, real=0.09 secs]
Total time for which application threads were stopped: 0.2053870 seconds
Application time: 0.0006161 seconds
Total time for which application threads were stopped: 0.5625090 seconds
def new generation
total 78656K, used 2190K [0xx29bebe0000)
eden space 69952K,
3% used [0xx248b3bd8, 0x28ae0000)
from space 8704K,
0% used [0x28aeae60000)
space 8704K,
0% used [0xxx29be0000)
tenured generation
total 174784K, used 100892K [0x29be990000)
the space 174784K,
57% used [0x29befe6fe690000)
compacting perm gen
total 12288K, used 371K [0xxx)
the space 12288K,
3% used [0xx346ecf38, 0x346ed000, 0x)
ro space 10240K,
55% used [0xx38c1c190000)
rw space 12288K,
55% used [0xx, 0xx39c90000)
Application time: 0.0016332 seconds
&&&&推荐文章:
【上篇】【下篇】eclipse启动优化（一）
阅读：6844次
&首先了解下JVM中几个相关的概念：
Xms：最小堆大小
Xmx：最大堆大小
Xmn：年轻代堆大小
Xss：每个线程的堆大小
PermSize：初始持久代大小
MaxPermSize：最大持久代大小
一般Xms、Xmx设置相同，PermSize、MaxPermSize设置相同，这样可以避免伸缩堆大小带来的性能损耗。
首先eclipse安装根目录下打开eclipse.ini，加上配置：
-Xloggc:gc.log
-XX:+PrintGCTimeStamps
-XX:+PrintGCDetails
目的是运行eclipse的时候可以打出详细gc过程。
启动eclipse，然后打开gc.log一看，哇塞启动一次就做了几十次GC，包括不少次Full GC，着手优化&&
先解决Full GC的问题：
3.159: [Full GC 3.159: [Tenured: 22716K-&2K), 0.1116536 secs] 38493K-&2K), [Perm : 20479K-&2K)], 0.1117614 secs] [Times: user=0.11 sys=0.00, real=0.11 secs]&
3.706: [Full GC 3.706: [Tenured: 26133K-&2K), 0.1235449 secs] 40042K-&2K), [Perm : 24575K-&2K)], 0.1236474 secs] [Times: user=0.13 sys=0.00, real=0.13 secs]&
如上GC日志可以看出，Full GC主要是针对Tenured、Perm区的GC，好那先调整Perm大小，指定充裕的持久代区域，eclipse.ini中加入：
-XX:PermSize=128m
-XX:MaxPermSize=128m
再次启动看gc.log，Full GC没有了，但是还有很多次普通GC，说明还是需要进一步优化。
eclipse的初始堆大小分配得很小，因此不利于年轻代堆大小的分配，如果设置的年轻代堆大小Xmn大于最小堆大小Xms，eclipse将无法启动。
因此，将Xms调整为512m，重启动后观察GC大幅减少。
最后调整Xmn，年轻代堆大小，经过反复比较后，发现设置&-Xmn256m&效果最优。
优化后的GC日志：
3.203: [GC 3.204: [DefNew: 209776K-&2K), 0.0876304 secs] 209776K-&2K), 0.0876921 secs] [Times: user=0.09 sys=0.00, real=0.09 secs]&
5.422: [GC 5.422: [DefNew: 235968K-&1K), 0.0989335 secs] 236976K-&3K), 0.0990229 secs]
在接近6秒的启动时间内，eclipse总共只做了2次普通GC回收，怎么样效果明显吧！
原文出处：http://blog.csdn.net/tomato8524/article/details/7428742
（转载本站文章请注明作者和出处
，请勿用于任何商业用途）
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如何在eclipse dump Java内存占用情况和打印GC LOG
当使用java开发应用程序发生内存泄露的时候，经常会需要dump内存，然后使用内存分析工具，比如Eclipse Memory Analyzer(一般称作MAT)工具。
本文将介绍如何在eclipse中dump 内存。
提前准备：
一、下载ＭＡＴ ：
二、测试代码如下：
package com.memoryLeakA
import java.util.ArrayL
import java.util.L
public class MemoryLeakDemo {
public static void main(String[] args) {
List&String& list = new ArrayList&String&();
while (true) {
list.add(&OutOfMemoryError soon&);
右键选择 run configurations&
找到Arguments -----&VM arguments&
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=c:/memoryLeakDemo.hprof
-XX:+PrintGCDetails&
-XX:+PrintGCDateStamps&
-XX:+PrintGCApplicationConcurrentTime
-XX:+PrintGCApplicationStoppedTime &
-Xloggc:c:/memoryLeakDemoGc.log
点击Run运行。即可出现内存dump现象：
在c:/test目录下会出现两个文件：
其中memoryLeakDemo.hprof为dump的内存情况。
memoryleakDemoGc.log为打印的jvm gc 垃圾回收情况
Eclipse Memory Analyzer（MAT)打开
memoryLeakDemo.hprof ，即可看到可疑的内存泄露情况，如下图：
memoryleakDemoGc.log日志：
出现类似于下图情况，可根据日志分析垃圾回收情况，从而分析JVM 内存使用情况。关于GC日志如何分析，请google之，将来会写文章介绍。
Application time: 0.0072104 seconds
T18:08:09.518+: [GC 0.079: [DefNew: 4017K-&261K(4928K), 0.0020189 secs] 4017K-&K), 0.0020804 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]&
Total time for which application threads were stopped: 0.0118427 seconds
Application time: 0.0015514 seconds
T18:08:09.531+: [GC 0.092: [DefNew: 2095K-&0K(4928K), 0.0022178 secs] 3258K-&K), 0.0022986 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]&
Total time for which application threads were stopped: 0.0023873 seconds
Application time: 0.0021970 seconds
T18:08:09.536+: [GC 0.097: [DefNew: 2618K-&0K(4928K), 0.0027436 secs] 5788K-&K), 0.0027797 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]&
Total time for which application threads were stopped: 0.0029137 seconds
Application time: 0.0033047 seconds
T18:08:09.542+: [GC 0.103: [DefNew: 3927K-&0K(4928K), 0.0040692 secs]0.107: [Tenured: 9715K-&K), 0.0078907 secs] 9715K-&K), [Perm : 376K-&376K(12288K)], 0.0120529 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]&
Total time for which application threads were stopped: 0.0121337 seconds
Application time: 0.0051220 seconds
T18:08:09.559+: [GC 0.120: [DefNew: 0K-&0K(4992K), 0.0019689 secs]0.122: [Tenured: 10078K-&K), 0.0086661 secs] 10078K-&K), [Perm : 376K-&376K(12288K)], 0.0107276 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]&
Total time for which application threads were stopped: 0.0108428 seconds
Application time: 0.0088859 seconds
T18:08:09.579+: [GC 0.140: [DefNew: 0K-&0K(4992K), 0.0026499 secs]0.143: [Tenured: 14987K-&K), 0.0113583 secs] 14987K-&K), [Perm : 376K-&376K(12288K)], 0.0141102 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]&
Total time for which application threads were stopped: 0.0142300 seconds
Application time: 0.0131855 seconds
T18:08:09.606+: [GC 0.167: [DefNew: 0K-&0K(8960K), 0.0041453 secs]0.172: [Tenured: 22350K-&1K), 0.0153709 secs] 22350K-&1K), [Perm : 376K-&376K(12288K)], 0.0196298 secs] [Times: user=0.01 sys=0.00, real=0.02 secs]&
Total time for which application threads were stopped: 0.0197569 seconds
Application time: 0.0192821 seconds
T18:08:09.646+: [GC 0.207: [DefNew: 0K-&0K(14976K), 0.0057633 secs]0.212: [Tenured: 33395K-&2K), 0.0206766 secs] 33395K-&2K), [Perm : 376K-&376K(12288K)], 0.0265551 secs] [Times: user=0.03 sys=0.00, real=0.03 secs]&
Total time for which application threads were stopped: 0.0266673 seconds
Application time: 0.0289176 seconds
T18:08:09.701+: [GC 0.262: [DefNew: 0K-&0K(23872K), 0.0086104 secs]0.271: [Tenured: 49962K-&3K), 0.0294036 secs] 49962K-&3K), [Perm : 376K-&376K(12288K)], 0.0380994 secs] [Times: user=0.03 sys=0.00, real=0.04 secs]&
Total time for which application threads were stopped: 0.0382799 seconds
Application time: 0.0436154 seconds
T18:08:09.783+: [GC 0.344: [DefNew: 0K-&0K(23872K), 0.0131421 secs]0.357: [Tenured: 74812K-&4K), 0.0415558 secs] 74812K-&4K), [Perm : 376K-&376K(12288K)], 0.0548393 secs] [Times: user=0.05 sys=0.00, real=0.06 secs]&
Total time for which application threads were stopped: 0.0550578 seconds
Application time: 0.0657430 seconds
T18:08:09.904+: [GC 0.465: [DefNew: 0K-&0K(43968K), 0.0198380 secs]0.485: [Tenured: 112088K-&6K), 0.0608105 secs] 112088K-&6K), [Perm : 376K-&376K(12288K)], 0.0807997 secs] [Times: user=0.08 sys=0.00, real=0.08 secs]&
Total time for which application threads were stopped: 0.0809335 seconds
Application time: 0.0991039 seconds
T18:08:10.084+: [GC 0.645: [DefNew: 0K-&0K(74240K), 0.0293317 secs]0.674: [Tenured: 168002K-&4784K), 0.0895410 secs] 168002K-&9024K), [Perm : 376K-&376K(12288K)], 0.1189829 secs] [Times: user=0.12 sys=0.00, real=0.12 secs]&
T18:08:10.203+: [Full GC 0.764: [Tenured: 100905K-&4784K), 0.0861601 secs] 100905K-&3440K), [Perm : 376K-&371K(12288K)], 0.0862167 secs] [Times: user=0.08 sys=0.00, real=0.09 secs]&
Total time for which application threads were stopped: 0.2053870 seconds
Application time: 0.0006161 seconds
Total time for which application threads were stopped: 0.5625090 seconds
def new generation & total 78656K, used 2190K [0xx29bebe0000)
eden space 69952K, & 3% used [0xx248b3bd8, 0x28ae0000)
from space 8704K, & 0% used [0x28aeae60000)
to & space 8704K, & 0% used [0xxx29be0000)
tenured generation & total 174784K, used 100892K [0x29be990000)
the space 174784K, &57% used [0x29befe6fe690000)
compacting perm gen &total 12288K, used 371K [0xxx)
the space 12288K, & 3% used [0xx346ecf38, 0x346ed000, 0x)
ro space 10240K, &55% used [0xx38c1c190000)
rw space 12288K, &55% used [0xx, 0xx39c90000)
Application time: 0.0016332 seconds
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