简介从JDK8开始,永久代(PermGen)的概念被废弃掉了,取而代之的是一个称为Metaspace的存储空间。Metaspace使用的是本地内存,而不是堆内存,也就是说在默认情况下Metaspace的大小只与本地内存大小有关。当然你也可以通过以下的几个参数对Metaspace进行控制:
测试代码下面会针对这个参数对Metaspace做一个粗略的展示。
上面的程序的大致意思是,不断的生成新的类, 然后让类加载器去加载这个类,同时将其保存下来,避免GC回收掉。这里使用到了ASM框架 测试参数在运行该程序的时候加上如下的JVM参数,第一个参数用于打印GC日志,第二个参数用于打印对应的时间戳。 -XX:+PrintGCDetails -XX:+PrintGCDateStamps 运行程序后,打印出的第一行日志显示, 2015-07-05T16:26:53.708+0800: [GC (Metadata GC Threshold) [PSYoungGen: 13978K->3229K(38400K)] 13978K->3237K(125952K), 0.0043062 secs] [Times: user=0.06 sys=0.02, real=0.00 secs]
2015-07-05T16:26:53.712+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 3229K->0K(38400K)] [ParOldGen: 8K->3111K(60928K)] 3237K->3111K(99328K), [Metaspace: 5699K->5699K(1064960K)], 0.0110314 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
奇怪的事情发生了,这里面显示的Metaspace大小为1064960K,将近1G,而不是前面提到的默认值20M左右。继续运行一段时间后出现了如下的异常, Exception in thread "main" java.lang.OutOfMemoryError: Compressed class space at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:760) at java.lang.ClassLoader.defineClass(ClassLoader.java:642) at Metaspace.main(Metaspace.java:37) 根据http://itdoc./manuals/link/has_v101001/0344211De/compressedclassspacesize.htm 这时JVM参数变为了, -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:-UseCompressedClassPointers 再一次运行程序,出现如下日志 2015-07-05T17:38:31.030+0800: [GC (Metadata GC Threshold) [PSYoungGen: 21301K->4984K(38400K)] 21301K->4992K(125952K), 0.0041727 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
2015-07-05T17:38:31.034+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 4984K->0K(38400K)] [ParOldGen: 8K->4789K(64512K)] 4992K->4789K(102912K), [Metaspace: 6922K->6922K(22528K)], 0.0147936 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
初始的Metaspace的大小变为了20M左右。由此猜想之前出现的问题是不是由于开启了压缩功能,而默认值-XX:CompressedClassSpaceSize=1G,其大于-XX:MetaspaceSize=20M,所以MetaspaceSize被设置为了1G。 -XX:MetaspaceSize的使用添加JVM参数,-XX:MetaspaceSize=100m, 这时的JVM参数变为, -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:-UseCompressedClassPointers -XX:MetaspaceSize=50M
运行后出现的日志为, 2015-07-05T17:53:20.430+0800: [GC (Allocation Failure) [PSYoungGen: 33280K->5100K(38400K)] 33280K->7635K(125952K), 0.0076185 secs] [Times: user=0.03 sys=0.03, real=0.01 secs]
2015-07-05T17:53:20.511+0800: [GC (Metadata GC Threshold) [PSYoungGen: 24676K->5102K(71680K)] 27211K->11885K(159232K), 0.0085707 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
2015-07-05T17:53:20.519+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 5102K->0K(71680K)] [ParOldGen: 6782K->11703K(67584K)] 11885K->11703K(139264K), [Metaspace: 13581K->13581K(51200K)], 0.0442425 secs] [Times: user=0.19 sys=0.00, real=0.04 secs]
默认的初始值变为了50M,可见设置的参数生效了。 -XX:MaxMetaspaceSize的使用添加JVM参数,-XX:MaxMetaspaceSize=100m, 这时的JVM参数变为, -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:-UseCompressedClassPointers -XX:MetaspaceSize=50M -XX:MaxMetaspaceSize=100m
运行后出现的日志为, 2015-07-05T18:04:10.000+0800: [GC (Allocation Failure) [PSYoungGen: 33280K->5116K(38400K)] 33280K->7627K(125952K), 0.0069565 secs] [Times: user=0.08 sys=0.00, real=0.01 secs] 2015-07-05T18:04:10.086+0800: [GC (Metadata GC Threshold) [PSYoungGen: 24689K->5102K(71680K)] 27199K->11917K(159232K), 0.0092239 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 2015-07-05T18:04:10.095+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 5102K->0K(71680K)] [ParOldGen: 6814K->11703K(74240K)] 11917K->11703K(145920K), [Metaspace: 13581K->13581K(51200K)], 0.0636790 secs] [Times: user=0.20 sys=0.00, real=0.06 secs] 2015-07-05T18:04:10.297+0800: [GC (Metadata GC Threshold) [PSYoungGen: 37664K->5106K(71680K)] 49367K->19785K(145920K), 0.0066032 secs] [Times: user=0.11 sys=0.00, real=0.01 secs] 2015-07-05T18:04:10.304+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 5106K->0K(71680K)] [ParOldGen: 14679K->19664K(129536K)] 19785K->19664K(201216K), [Metaspace: 21181K->21181K(86016K)], 0.0752276 secs] [Times: user=0.45 sys=0.02, real=0.08 secs] 2015-07-05T18:04:10.454+0800: [GC (Metadata GC Threshold) [PSYoungGen: 19414K->4219K(82432K)] 39079K->23884K(211968K), 0.0048493 secs] [Times: user=0.11 sys=0.00, real=0.01 secs] 2015-07-05T18:04:10.459+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 4219K->0K(82432K)] [ParOldGen: 19664K->23672K(187392K)] 23884K->23672K(269824K), [Metaspace: 24981K->24981K(102400K)], 0.0569726 secs] [Times: user=0.33 sys=0.00, real=0.06 secs] 2015-07-05T18:04:10.516+0800: [GC (Last ditch collection) [PSYoungGen: 0K->0K(88064K)] 23672K->23672K(275456K), 0.0021137 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 2015-07-05T18:04:10.518+0800: [Full GC (Last ditch collection) [PSYoungGen: 0K->0K(88064K)] [ParOldGen: 23672K->23655K(274944K)] 23672K->23655K(363008K), [Metaspace: 24981K->24981K(102400K)], 0.1025192 secs] [Times: user=0.69 sys=0.00, real=0.10 secs] Exception in thread "main" java.lang.OutOfMemoryError: Metaspace at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:760) at java.lang.ClassLoader.defineClass(ClassLoader.java:642) at Metaspace.main(Metaspace.java:37) 当Metaspace的空间增长到100M的时候,还需要继续增长,但是由于之前设置了Metaspace的最大值为100M,因此抛出了上面的异常。 -XX:MinMetaspaceFreeRatio的使用添加JVM参数,-XX:MinMetaspaceFreeRatio=65(注意此时-XX:MaxMetaspaceFreeRatio为70,min需要小于max,所以设置为), 这时的JVM参数变为 -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:-UseCompressedClassPointers -XX:MetaspaceSize=50M -XX:MaxMetaspaceSize=100m -XX:MinMetaspaceFreeRatio=65
运行后的日志为, 2015-07-05T18:32:06.476+0800: [GC (Allocation Failure) [PSYoungGen: 33280K->5100K(38400K)] 33280K->7595K(125952K), 0.0093795 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 2015-07-05T18:32:06.555+0800: [GC (Metadata GC Threshold) [PSYoungGen: 24677K->5102K(71680K)] 27172K->11893K(159232K), 0.0077681 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 2015-07-05T18:32:06.563+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 5102K->0K(71680K)] [ParOldGen: 6790K->11703K(71680K)] 11893K->11703K(143360K), [Metaspace: 13581K->13581K(51200K)], 0.0424761 secs] [Times: user=0.16 sys=0.02, real=0.04 secs] 2015-07-05T18:32:06.826+0800: [GC (Metadata GC Threshold) [PSYoungGen: 55855K->5115K(71680K)] 67559K->23867K(143360K), 0.0121986 secs] [Times: user=0.06 sys=0.00, real=0.01 secs] 2015-07-05T18:32:06.838+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 5115K->0K(71680K)] [ParOldGen: 18751K->23672K(128000K)] 23867K->23672K(199680K), [Metaspace: 24981K->24981K(102400K)], 0.0786608 secs] [Times: user=0.31 sys=0.00, real=0.08 secs] 2015-07-05T18:32:06.917+0800: [GC (Last ditch collection) [PSYoungGen: 0K->0K(81920K)] 23672K->23672K(209920K), 0.0018780 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 2015-07-05T18:32:06.919+0800: [Full GC (Last ditch collection) [PSYoungGen: 0K->0K(81920K)] [ParOldGen: 23672K->23655K(179200K)] 23672K->23655K(261120K), [Metaspace: 24981K->24981K(102400K)], 0.0771198 secs] [Times: user=0.34 sys=0.00, real=0.08 secs] Exception in thread "main" java.lang.OutOfMemoryError: Metaspace at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:760) at java.lang.ClassLoader.defineClass(ClassLoader.java:642) at Metaspace.main(Metaspace.java:37) 似乎与之前没什么区别,但是仔细可以发现相比于不设置该参数少了一次FullGC。 -XX:MinMetaspaceExpansion去掉之前设置的-XX:MinMetaspaceFreeRatio,同时设置-XX:MinMetaspaceExpansion=100M,修改-XX:MaxMetaspaceSize为300M,此时的JVM参数为, -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:-UseCompressedClassPointers -XX:MetaspaceSize=50M -XX:MaxMetaspaceSize=300M -XX:MinMetaspaceExpansion=100M运行后的日志为, 2015-07-05T18:53:25.466+0800: [GC (Allocation Failure) [PSYoungGen: 33280K->5100K(38400K)] 33280K->7607K(125952K), 0.0067215 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 2015-07-05T18:53:25.553+0800: [GC (Metadata GC Threshold) [PSYoungGen: 24676K->5102K(71680K)] 27183K->11881K(159232K), 0.0080541 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 2015-07-05T18:53:25.561+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 5102K->0K(71680K)] [ParOldGen: 6778K->11771K(73216K)] 11881K->11771K(144896K), [Metaspace: 13580K->13580K(51200K)], 0.0469926 secs] [Times: user=0.14 sys=0.00, real=0.05 secs] 2015-07-05T18:53:25.875+0800: [GC (Allocation Failure) [PSYoungGen: 66560K->5115K(71680K)] 78331K->26463K(144896K), 0.0146596 secs] [Times: user=0.06 sys=0.00, real=0.02 secs] 2015-07-05T18:53:26.110+0800: [GC (Metadata GC Threshold) [PSYoungGen: 48338K->5113K(91648K)] 69686K->35925K(164864K), 0.0151956 secs] [Times: user=0.05 sys=0.01, real=0.02 secs] 2015-07-05T18:53:26.125+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 5113K->0K(91648K)] [ParOldGen: 30811K->35633K(147456K)] 35925K->35633K(239104K), [Metaspace: 36381K->36381K(153600K)], 0.1574835 secs] [Times: user=0.66 sys=0.00, real=0.16 secs] 2015-07-05T18:53:26.818+0800: [GC (Allocation Failure) [PSYoungGen: 86528K->5109K(91648K)] 122161K->54855K(239104K), 0.0200557 secs] [Times: user=0.06 sys=0.00, real=0.02 secs] 2015-07-05T18:53:27.015+0800: [GC (Metadata GC Threshold) [PSYoungGen: 29014K->10133K(127488K)] 78760K->59879K(274944K), 0.0116375 secs] [Times: user=0.05 sys=0.02, real=0.01 secs] 2015-07-05T18:53:27.027+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 10133K->0K(127488K)] [ParOldGen: 49745K->59524K(221696K)] 59879K->59524K(349184K), [Metaspace: 59182K->59182K(256000K)], 0.2163024 secs] [Times: user=1.05 sys=0.00, real=0.22 secs] 2015-07-05T18:53:27.691+0800: [GC (Metadata GC Threshold) [PSYoungGen: 56721K->12448K(127488K)] 116245K->71972K(349184K), 0.0139748 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 2015-07-05T18:53:27.705+0800: [Full GC (Metadata GC Threshold) [PSYoungGen: 12448K->0K(127488K)] [ParOldGen: 59524K->71563K(306176K)] 71972K->71563K(433664K), [Metaspace: 70582K->70582K(307200K)], 0.1479683 secs] [Times: user=0.55 sys=0.00, real=0.15 secs] 2015-07-05T18:53:27.853+0800: [GC (Last ditch collection) [PSYoungGen: 0K->0K(144384K)] 71563K->71563K(450560K), 0.0045973 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 2015-07-05T18:53:27.857+0800: [Full GC (Last ditch collection) [PSYoungGen: 0K->0K(144384K)] [ParOldGen: 71563K->71546K(386048K)] 71563K->71546K(530432K), [Metaspace: 70582K->70582K(307200K)], 0.2734107 secs] [Times: user=1.65 sys=0.00, real=0.27 secs] Exception in thread "main" java.lang.OutOfMemoryError: Metaspace at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:760) at java.lang.ClassLoader.defineClass(ClassLoader.java:642) at Metaspace.main(Metaspace.java:37) 可以看出每次Metaspace空间的增长都在100MB左右,经历了3次的FullGC之后空间就达到了设置的上限300MB。 -XX:MinMetaspaceFreeRatio和-XX:MinMetaspaceExpansion为了说明这二者有什么影响设置如下参数, -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:-UseCompressedClassPointers -XX:MetaspaceSize=50M -XX:MaxMetaspaceSize=500m -XX:MinMetaspaceExpansion=50M -XX:MaxMetaspaceExpansion=50M -XX:MinMetaspaceFreeRatio=5之后修改MinMetaspaceFreeRatio的为20,35,50,65分别可以得到如下的GC数据 5 2015-07-05T20:47:47.444+0800: ... [Metaspace: 13580K->13580K(51200K)]... 2015-07-05T20:47:47.741+0800: ... [Metaspace: 24981K->24981K(102400K)]... 2015-07-05T20:47:48.150+0800: ... [Metaspace: 36381K->36381K(153600K)]... 2015-07-05T20:47:48.584+0800: ... [Metaspace: 47781K->47781K(204800K)]... 2015-07-05T20:47:49.124+0800: ... [Metaspace: 59182K->59182K(256000K)]... 2015-07-05T20:47:49.717+0800: ... [Metaspace: 70582K->70582K(307200K)]... 2015-07-05T20:47:50.462+0800: ... [Metaspace: 81982K->81982K(358400K)]... 2015-07-05T20:47:51.278+0800: ... [Metaspace: 93382K->93382K(409600K)]... 2015-07-05T20:47:52.272+0800: ... [Metaspace: 104782K->104782K(460800K)]... 2015-07-05T20:47:53.418+0800: ... [Metaspace: 116182K->116182K(512000K)]... 20 2015-07-05T20:50:16.123+0800: ... [Metaspace: 13580K->13580K(51200K)]... 2015-07-05T20:50:16.404+0800: ... [Metaspace: 24981K->24981K(102400K)]... 2015-07-05T20:50:16.754+0800: ... [Metaspace: 36381K->36381K(153600K)]... 2015-07-05T20:50:17.234+0800: ... [Metaspace: 47781K->47781K(204800K)]... 2015-07-05T20:50:17.758+0800: ... [Metaspace: 59182K->59182K(256000K)]... 2015-07-05T20:50:18.499+0800: ... [Metaspace: 73432K->73432K(321536K)]... 2015-07-05T20:50:19.591+0800: ... [Metaspace: 91244K->91244K(401408K)]... 2015-07-05T20:50:21.326+0800: ... [Metaspace: 113510K->113510K(501760K)]... 2015-07-05T20:50:21.868+0800: ... [Metaspace: 116182K->116182K(512000K)]... 35 2015-07-05T20:56:02.338+0800: ... [Metaspace: 13581K->13581K(51200K)]... 2015-07-05T20:56:02.619+0800: ... [Metaspace: 24981K->24981K(102400K)]... 2015-07-05T20:56:03.010+0800: ... [Metaspace: 37258K->37258K(157696K)]... 2015-07-05T20:56:03.733+0800: ... [Metaspace: 56146K->56146K(243712K)]... 2015-07-05T20:56:05.233+0800: ... [Metaspace: 85206K->85206K(374784K)]... 2015-07-05T20:56:07.548+0800: ... [Metaspace: 116182K->116182K(512000K)]... 50 2015-07-05T20:59:08.866+0800: ... [Metaspace: 13580K->13580K(51200K)]... 2015-07-05T20:59:09.153+0800: ... [Metaspace: 24981K->24981K(102400K)]... 2015-07-05T20:59:09.863+0800: ... [Metaspace: 47781K->47781K(204800K)]... 2015-07-05T20:59:12.178+0800: ... [Metaspace: 93382K->93382K(409600K)]... 2015-07-05T20:59:14.031+0800: ... [Metaspace: 116182K->116182K(512000K)]... 65 2015-07-05T21:01:03.353+0800: ... [Metaspace: 13581K->13581K(51200K)]... 2015-07-05T21:01:03.888+0800: ... [Metaspace: 34753K->34753K(147456K)]... 2015-07-05T21:01:06.648+0800: ... [Metaspace: 95245K->95245K(419840K)]... 2015-07-05T21:01:08.547+0800: ... [Metaspace: 116182K->116182K(512000K)]... 从上面的数据可以看出 参考资料http://www./TakahiroYamada3/tools-for-metaspace |
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