JVM调优调的是什么？是寂寞吗？

不,是GC。

gc永远会是Java程序员需要考虑的不稳定因素之一。对JVM内存的系统级的调优主要的目的是减少GC的频率和Full GC的次数。

而GC的情景复杂又复杂，为了能更深刻的了解内存模型，参考《深入java虚拟机理解》，不定期更新JVM入门。

我自己遇到过一次内存泄漏，但不是线上环境，本地环境出现过一次，后来重新推包解决了，没有复现，那么平时的自用服务器突然内存与磁盘IO暴增，你会如何调优？定位到具体线程后，是因为大对象占用空间造成，还是程序死循环了你如何解决？，关于JVM入门，以及JVM调优整理了地址请转至

https://kkget.github.io/2020/09/24/JVM调优相关https://kkget.github.io/2020/10/13/JVM从入门到放弃

以上内容不定期更新，今天主要从性能监控工具以及整理关于调优相关部分。

虚拟机性能监控工具

1.jps(JVM Porcess Status Tool)

功能：列出正在运行的虚拟机程序并显示执行主类名称以及进程ID(LVMID ,Local Virtiual Machine Identifier)。

jps -l  输出主类的全类名jps -v  输出虚拟机启动时的JVM参数格式 jps [ options ] [ hostid ][root@zhaokk shell]# jps -v2288193 Jps -Denv.class.path=$:CLASSPATH:/opt/soft/jdk/jdk1.8.0_261/lib/ -Dapplication.home=/opt/soft/jdk/jdk1.8.0_261 -Xms8m2171556 jar -Xmx1024m2195236 jar -Xmx1024m2172742 jar -Xmx1024m1351582 jar -Xmx1024m2136682 jar -Xmx1024m2236393 jar2240457 jar -Xmx1024m2135436 jar -Xmx1024m2286668 jar -Xmx1024m3087 jar -Xmx1024m2160978 jar -Xmx1024m2176083 jar -Xmx1024m2287761 jar2196085 jar -Xmx1024m

2.jstat(JVM Statistics Monitoring Tool)

jstat [option vmid]jstat -gc 2764 250 20[root@zhaokk shell]# jstat -gc 1477 250 20 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT   1536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.6401536.0 1536.0  0.0   110.5  12480.0   2207.5   31084.0    24310.8   24320.0 23552.8 2560.0 2340.8    259    0.589   1      0.051    0.640

jstat -gcutil 2764[root@zhaokk shell]# jstat -gcutil 1477  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT     0.00   7.19  19.05  78.21  96.85  91.44    259    0.589     1    0.051    0.640

3.jinfo java配置信息(Configuration Info for java)

格式  jinfo [option] pid

4.jmap (Memory Map for java) java内存映射工具

格式 jmap [option] vmid
jmap -heap [root@zhaokk shell]# jmap -heap 1477Attaching to process ID 1477, please wait...Debugger attached successfully.Server compiler detected.JVM version is 25.11-b03
using thread-local object allocation.Mark Sweep Compact GC
Heap Configuration:   MinHeapFreeRatio         = 40   MaxHeapFreeRatio         = 70   MaxHeapSize              = 482344960 (460.0MB)   NewSize                  = 1310720 (1.25MB)   MaxNewSize               = 160759808 (153.3125MB)   OldSize                  = 30146560 (28.75MB)   NewRatio                 = 2   SurvivorRatio            = 8   MetaspaceSize            = 21807104 (20.796875MB)   CompressedClassSpaceSize = 1073741824 (1024.0MB)   MaxMetaspaceSize         = 17592186044415 MB   G1HeapRegionSize         = 0 (0.0MB)
Heap Usage:New Generation (Eden + 1 Survivor Space):   capacity = 14352384 (13.6875MB)   used     = 4124624 (3.9335479736328125MB)   free     = 10227760 (9.753952026367188MB)   28.738250035673516% usedEden Space:   capacity = 12779520 (12.1875MB)   used     = 4011512 (3.8256759643554688MB)   free     = 8768008 (8.361824035644531MB)   31.390161758814102% usedFrom Space:   capacity = 1572864 (1.5MB)   used     = 113112 (0.10787200927734375MB)   free     = 1459752 (1.3921279907226562MB)   7.19146728515625% usedTo Space:   capacity = 1572864 (1.5MB)   used     = 0 (0.0MB)   free     = 1572864 (1.5MB)   0.0% usedtenured generation:   capacity = 31830016 (30.35546875MB)   used     = 24894208 (23.740966796875MB)   free     = 6935808 (6.614501953125MB)   78.20985072706216% used15847 interned Strings occupying 1391576 bytes.

5.jhat (JVM Heap Analysis Tool)虚拟机堆转快照分析工具用的比较少

6.jstack java堆栈追踪工具(stack Trace for java) 生成当前的线程快照

格式 jstack [option] vmid[root@zhaokk bin]# jstack -l 14772020-10-20 15:40:50Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.11-b03 mixed mode):
"Attach Listener" #27 daemon prio=9 os_prio=0 tid=0x00007fc928003800 nid=0x446f waiting on condition [0x0000000000000000]   java.lang.Thread.State: RUNNABLE
   Locked ownable synchronizers:  - None
"http-bio-8080-AsyncTimeout" #25 daemon prio=5 os_prio=0 tid=0x00007fc95039f000 nid=0x5de waiting on condition [0x00007fc92d0cb000]   java.lang.Thread.State: TIMED_WAITING (sleeping)  at java.lang.Thread.sleep(Native Method)  at org.apache.tomcat.util.net.JIoEndpoint$AsyncTimeout.run(JIoEndpoint.java:153)  at java.lang.Thread.run(Thread.java:745)
   Locked ownable synchronizers:  - None
"http-bio-8080-Acceptor-0" #24 daemon prio=5 os_prio=0 tid=0x00007fc95039d800 nid=0x5dd runnable [0x00007fc92d1cc000]   java.lang.Thread.State: RUNNABLE  at java.net.PlainSocketImpl.socketAccept(Native Method)  at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:404)  at java.net.ServerSocket.implAccept(ServerSocket.java:545)  at java.net.ServerSocket.accept(ServerSocket.java:513)  at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:60)  at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:223)  at java.lang.Thread.run(Thread.java:745)   Locked ownable synchronizers: