记录一次JVM调优

首先查看服务器版本默认信息：

修改tomcat/bin/catalina.sh，在最顶端加入JAVA_OPTS="$JAVA_OPTS -XX:+PrintGCDetails -Xloggc:/usr/local/java/apache-tomcat-7.0.78/bin/gc.log"

随后在 -Xloggc指定路径下，打开gc.log，部分信息如下：

[GC (Allocation Failure) [PSYoungGen: 15872K->2544K(18432K)] 15872K->4199K(60928K), 0.0076594 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
0.801: [GC (Allocation Failure) [PSYoungGen: 18416K->2554K(34304K)] 20071K->7458K(76800K), 0.0084303 secs] [Times: user=0.01 sys=0.00, real=0.01 secs]
1.102: [GC (Allocation Failure) [PSYoungGen: 34298K->2532K(34304K)] 39202K->10385K(76800K), 0.0073978 secs] [Times: user=0.01 sys=0.00, real=0.01 secs]
1.324: [GC (Allocation Failure) [PSYoungGen: 34276K->2540K(66048K)] 42129K->14849K(108544K), 0.0077529 secs] [Times: user=0.01 sys=0.00, real=0.01 secs]
1.538: [GC (Allocation Failure) [PSYoungGen: 66028K->2542K(66048K)] 78337K->25278K(108544K), 0.0107662 secs] [Times: user=0.01 sys=0.00, real=0.01 secs]
1.710: [GC (Allocation Failure) [PSYoungGen: 66030K->11795K(137216K)] 88766K->34540K(179712K), 0.0176510 secs] [Times: user=0.03 sys=0.01, real=0.02 secs]
2.065: [GC (Allocation Failure) [PSYoungGen: 136723K->14318K(139264K)] 159468K->48794K(181760K), 0.0246635 secs] [Times: user=0.04 sys=0.00, real=0.03 secs]
2.090: [Full GC (Ergonomics) [PSYoungGen: 14318K->2377K(139264K)] [ParOldGen: 34476K->42413K(78848K)] 48794K->44791K(218112K), [Metaspace: 13713K->13713K(1062912K)], 0.0826740 secs] [Times: user=0.15 sys=0.01, real=0.08 secs]
2.488: [GC (Allocation Failure) [PSYoungGen: 127305K->22522K(222720K)] 169719K->65057K(301568K), 0.0318258 secs] [Times: user=0.06 sys=0.00, real=0.03 secs]
3.086: [GC (Allocation Failure) [PSYoungGen: 222714K->26617K(268288K)] 265249K->87196K(347136K), 0.0409823 secs] [Times: user=0.07 sys=0.02, real=0.05 secs]
3.731: [GC (Allocation Failure) [PSYoungGen: 268281K->37864K(278016K)] 328860K->112315K(356864K), 0.0531917 secs] [Times: user=0.09 sys=0.02, real=0.05 secs]
3.785: [Full GC (Ergonomics) [PSYoungGen: 37864K->0K(278016K)] [ParOldGen: 74450K->59866K(113152K)] 112315K->59866K(391168K), [Metaspace: 13760K->13760K(1062912K)], 0.1234969 secs] [Times: user=0.24 sys=0.00, real=0.13 secs]
4.434: [GC (Allocation Failure) [PSYoungGen: 240128K->45645K(286208K)] 299994K->105511K(399360K), 0.0358239 secs] [Times: user=0.07 sys=0.00, real=0.04 secs]
4.989: [GC (Allocation Failure) [PSYoungGen: 285773K->42527K(269824K)] 345639K->109322K(382976K), 0.0452064 secs] [Times: user=0.09 sys=0.01, real=0.04 secs]
5.489: [GC (Allocation Failure) [PSYoungGen: 260127K->37422K(255488K)] 326922K->110639K(368640K), 0.0331642 secs] [Times: user=0.06 sys=0.00, real=0.03 secs]
7.060: [GC (Allocation Failure) [PSYoungGen: 255022K->11882K(278016K)] 328239K->89219K(391168K), 0.0199962 secs] [Times: user=0.03 sys=0.00, real=0.02 secs]

7.328: [GC (Metadata GC Threshold) [PSYoungGen: 65740K->160K(276480K)] 143076K->81525K(389632K), 0.0071875 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
7.336: [Full GC (Metadata GC Threshold) [PSYoungGen: 160K->0K(276480K)] [ParOldGen: 81365K->30917K(90624K)] 81525K->30917K(367104K), [Metaspace: 23265K->23265K(1071104K)], 0.0701499 secs] [Times: user=0.12 sys=0.00, real=0.07 secs]
9.690: [GC (Allocation Failure) [PSYoungGen: 216064K->15373K(272896K)] 246981K->46298K(363520K), 0.0266823 secs] [Times: user=0.03 sys=0.00, real=0.02 secs]

9.819: [GC (Metadata GC Threshold) [PSYoungGen: 25761K->8213K(274944K)] 56686K->39146K(365568K), 0.0153547 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]
9.835: [Full GC (Metadata GC Threshold) [PSYoungGen: 8213K->0K(274944K)] [ParOldGen: 30933K->37095K(108032K)] 39146K->37095K(382976K), [Metaspace: 38475K->38475K(1083392K)], 0.0922216 secs] [Times: user=0.16 sys=0.00, real=0.09 secs]

77.664: [GC (Allocation Failure) [PSYoungGen: 217088K->56304K(242176K)] 254183K->119858K(350208K), 0.0250691 secs] [Times: user=0.04 sys=0.01, real=0.03 secs]
80.575: [GC (Allocation Failure) [PSYoungGen: 242160K->3375K(262144K)] 305714K->122388K(387072K), 0.0230121 secs] [Times: user=0.02 sys=0.02, real=0.03 secs]
80.599: [Full GC (Ergonomics) [PSYoungGen: 3375K->0K(262144K)] [ParOldGen: 119013K->108779K(213504K)] 122388K->108779K(475648K), [Metaspace: 54741K->54741K(1099776K)], 0.1379975 secs] [Times: user=0.24 sys=0.00, real=0.13 secs]

这里

-Xmx1038m：等价于-XX:MaxHeapSize，设置JVM最大堆内存为1038M。

-Xms64m：等价于-XX:InitialHeapSize，设置JVM初始堆内存为64M。

使用ParallelGC收集器

总共5次full gc，其中两次是元空间（jdk8默认值21.8M左右）引发的full gc，三次是HotSpot自动选择和调优引发的FullGC，自适应策略

改善：-XX:MetaspaceSize=64m 初始元空间大小

增加 JAVA_OPTS="$JAVA_OPTS -server -showversion -Xms512m -Xmx512m -XX:MetaspaceSize=64m"

如果-Xmx分配过大，会导致无法为其他tomcat分配内存：There is insufficient memory for the Java Runtime Environment to continue.这里尝试之后，选择512m

可以看见

Java HotSpot(TM) 64-Bit Server VM (25.144-b01) for linux-amd64 JRE (1.8.0_144-b01), built on Jul 21 2017 21:57:33 by "java_re" with gcc 4.3.0 20080428 (Red Hat 4.3.0-8)
Memory: 4k page, physical 4056480k(1077372k free), swap 0k(0k free)
CommandLine flags: -XX:InitialHeapSize=2147483648 -XX:MaxHeapSize=2147483648 -XX:MetaspaceSize=67108864 -XX:+PrintGC -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseParallelGC
2.563: [GC (Allocation Failure) [PSYoungGen: 524800K->85308K(611840K)] 524800K->85388K(2010112K), 0.1003043 secs] [Times: user=0.17 sys=0.02, real=0.10 secs]
3.991: [GC (Allocation Failure) [PSYoungGen: 610108K->87037K(611840K)] 610188K->103584K(2010112K), 0.1100503 secs] [Times: user=0.17 sys=0.04, real=0.11 secs]
5.245: [GC (Allocation Failure) [PSYoungGen: 611837K->87018K(611840K)] 628384K->140886K(2010112K), 0.1087186 secs] [Times: user=0.12 sys=0.03, real=0.11 secs]
8.794: [GC (Allocation Failure) [PSYoungGen: 611818K->62918K(611840K)] 665686K->116794K(2010112K), 0.0452909 secs] [Times: user=0.08 sys=0.00, real=0.04 secs]
38.881: [GC (Allocation Failure) [PSYoungGen: 587718K->87036K(611840K)] 641594K->186752K(2010112K), 0.1298147 secs] [Times: user=0.09 sys=0.12, real=0.13 secs]

在38ms之前是减少了4次full gc

继续改进，替换ParallelGC，改为CMS+ParNew的组合：

JAVA_OPTS="$JAVA_OPTS -XX:+PrintGCDetails -Xloggc:/usr/local/java/tomcat-robot-web/bin/gc.log"
JAVA_OPTS="$JAVA_OPTS -server -showversion -Xms512m -Xmx512m -XX:MetaspaceSize=96m" -Xmn128m //XX:MaxPermSize=96m
JAVA_OPTS="$JAVA_OPTS -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:MaxGCPauseMillis=200"
JAVA_OPTS="$JAVA_OPTS -XX:+UseCMSCompactAtFullCollection"

-XX:+ExplicitGCInvokesConcurrent //system.gc使用cms算法

-XX:+DisableExplicitGC//禁止system.gc

-Xmn128m

-XX:+HeapDumpOnOutOfMemoryError
JVM发生OOM时，生成一个堆存储快照文件

-XX:HeapDumpPath=/home/admin/logs/java.hprof
OOM快照文件的地址

-XX:SurvivorRatio=10
Eden与Survivor的占用比例,例如10表示，一个survivor区占用 1/10 的Eden内存，即1/12的新生代内存，
新生代有2个survivor，即S0和S1。所以survivor总共是占用新生代内存的 2/12，Eden与新生代的占比则为 10/12

-XX:+UseCMSCompactAtFullCollection
CMS开启碎片整理，CMS默认不会整理堆碎片，因此为了防止堆碎片引起full gc，可以开启该选项

-XX:+UseCompressedOops
启用指针压缩，在64位HotSpot中使用32位指针，默认64位会比32位的内存使用多出1.5倍

-XX:+PrintHeapAtGC 每一次GC前和GC后，都打印堆信息。
-XX:+CMSClassUnloadingEnabled //对方法区gc

猜你喜欢