标签：real cti 阈值 max 虚拟 ota 运行 res serial
大多数情况下，对象会在新生代Eden区中分配，当Eden区中没有足够空间时，虚拟机将发起一次Minor GC。
package com.wjz.demo; public class HeapOOM { static class OOMObject {} /** * 使用 Serial / Serial Old 组合收集器 * -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:+UseSerialGC * @param args */ private static final int _1MB = 1024*1024; public static void main(String[] args) { byte[] b1, b2, b3, b4; b1 = new byte[2*_1MB]; b2 = new byte[2*_1MB]; b3 = new byte[2*_1MB]; b4 = new byte[4*_1MB]; // 此处会出现一次Minor GC } }
运行结果
[GC [DefNew: 6993K->554K(9216K), 0.0212177 secs] 6993K->6698K(19456K), 0.0318550 secs] [Times: user=0.00 sys=0.02, real=0.03 secs] Heap def new generation total 9216K, used 4978K [0x00000000f9a00000, 0x00000000fa400000, 0x00000000fa400000) eden space 8192K, 56% used [0x00000000f9a00000, 0x00000000f9e51fa0, 0x00000000fa200000) from space 1024K, 54% used [0x00000000fa300000, 0x00000000fa38a8b0, 0x00000000fa400000) to space 1024K, 0% used [0x00000000fa200000, 0x00000000fa200000, 0x00000000fa300000) tenured generation total 10240K, used 6144K [0x00000000fa400000, 0x00000000fae00000, 0x00000000fae00000) the space 10240K, 60% used [0x00000000fa400000, 0x00000000faa00030, 0x00000000faa00200, 0x00000000fae00000) compacting perm gen total 21248K, used 2556K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000) the space 21248K, 12% used [0x00000000fae00000, 0x00000000fb07f258, 0x00000000fb07f400, 0x00000000fc2c0000) No shared spaces configured.
eden space 8192K：新生代Eden区
from space 1024K：新生代from survivor区
to space 1024K：新生代to survivor区
the space 10240K：老年代区
结果分析
新生代内存占用量由6993K降到554K，总内存占用量由6993K升到6998K几乎没有变化。3个2M对象分配内存时放入了新生代Eden区，此时Eden区还剩2M左右的内存空间， 又来了一个4M对象想放进Eden区当时显然不可能，触发了一次Minor GC，复制算法开始将Eden区的对象复制到from survivor区，但是from survivor区只有1M空间，所以 只能将这3个2M对象通过分配担保转移到老年代中。4M对象被分配到了Eden区。
大对象是指需要大量连续空间的对象如字符串和数组。
package com.wjz.demo; public class HeapOOM { static class OOMObject {} /** * 使用 Serial / Serial Old 收集器 * -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:+UseSerialGC * -XX:PretenureSizeThreshold=3145728(仅Serial、PreNew有效) * @param args */ private static final int _1MB = 1024*1024; public static void main(String[] args) { byte[] b1; b1 = new byte[4*_1MB]; } }
运行结果
Heap def new generation total 9216K, used 1013K [0x00000000f9a00000, 0x00000000fa400000, 0x00000000fa400000) eden space 8192K, 12% used [0x00000000f9a00000, 0x00000000f9afd518, 0x00000000fa200000) from space 1024K, 0% used [0x00000000fa200000, 0x00000000fa200000, 0x00000000fa300000) to space 1024K, 0% used [0x00000000fa300000, 0x00000000fa300000, 0x00000000fa400000) tenured generation total 10240K, used 4096K [0x00000000fa400000, 0x00000000fae00000, 0x00000000fae00000) the space 10240K, 40% used [0x00000000fa400000, 0x00000000fa800010, 0x00000000fa800200, 0x00000000fae00000) compacting perm gen total 21248K, used 2553K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000) the space 21248K, 12% used [0x00000000fae00000, 0x00000000fb07e5d8, 0x00000000fb07e600, 0x00000000fc2c0000) No shared spaces configured.
结果分析
新生代Eden和survivor区几乎没有使用，老年区占用了40%，因为大于3M的对象直接分配到了老年代中。
设置-XX:MaxTenuringThreshold参数设置对象进入老年代的年龄阈值。
package com.wjz.demo; public class HeapOOM { static class OOMObject {} /** * 使用 Serial / Serial Old 收集器 * -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:+UseSerialGC * -XX:MaxTenuringThreshold=1 -XX:+PrintTenuringDistribution * @param args */ private static final int _1MB = 1024*1024; public static void main(String[] args) { byte[] b1, b2, b3, b4; b1 = new byte[_1MB/4]; b2 = new byte[4*_1MB]; b3 = new byte[4*_1MB]; b3 = null; b4 = new byte[4*_1MB]; } }
运行结果
[GC [DefNew Desired survivor size 524288 bytes, new threshold 1 (max 1) - age 1: 829632 bytes, 829632 total : 5201K->810K(9216K), 0.0036339 secs] 5201K->4906K(19456K), 0.0036706 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC [DefNew Desired survivor size 524288 bytes, new threshold 1 (max 1) - age 1: 256 bytes, 256 total : 5234K->0K(9216K), 0.0013901 secs] 9330K->4906K(19456K), 0.0014093 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] Heap def new generation total 9216K, used 4260K [0x00000000f9a00000, 0x00000000fa400000, 0x00000000fa400000) eden space 8192K, 52% used [0x00000000f9a00000, 0x00000000f9e28fd0, 0x00000000fa200000) from space 1024K, 0% used [0x00000000fa200000, 0x00000000fa200100, 0x00000000fa300000) to space 1024K, 0% used [0x00000000fa300000, 0x00000000fa300000, 0x00000000fa400000) tenured generation total 10240K, used 4906K [0x00000000fa400000, 0x00000000fae00000, 0x00000000fae00000) the space 10240K, 47% used [0x00000000fa400000, 0x00000000fa8ca8d0, 0x00000000fa8caa00, 0x00000000fae00000) compacting perm gen total 21248K, used 2556K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000) the space 21248K, 12% used [0x00000000fae00000, 0x00000000fb07f258, 0x00000000fb07f400, 0x00000000fc2c0000) No shared spaces configured.
标签：real cti 阈值 max 虚拟 ota 运行 res serial
原文地址：http://www.cnblogs.com/BINGJJFLY/p/7628674.html
