【JVM系列】JVM调优

talk is cheap, show me the dry cargo.

JVM调优工具详解

Software	version
OpenJDK	1.8

Jps常用命令（Java Virtual Machine Process Status Tool）

• jps -help

  root@CN02:/home/demo-server# jps -help
  usage: jps [-help]
         jps [-q] [-mlvV] []
  
  Definitions:
      :      [:]
  

• jps -mlv

  root@CN02:/home/demo-server# jps -mlv
  16082 demo-uat.jar --spring.profiles.active=uat -XX:+UseConcMarkSweepGC -Xmn512m -Xms768m -Xmx768m -Duser.timezone=GMT+08
  14339 sun.tools.jps.Jps -mlv -Dapplication.home=/usr/lib/jvm/java-8-openjdk-amd64 -Xms8m
  15509 demo-test.jar --spring.profiles.active=test -XX:+UseConcMarkSweepGC -Xmn512m -Xms768m -Xmx768m -Duser.timezone=GMT+08
  

Jstat常用命令（JVM统计监测工具）

• jstat -help

  root@CN02:/home/demo-server# jstat -help
  Usage: jstat -help|-options
         jstat - [-t] [-h]  [ []]
  
  Definitions:
          An option reported by the -options option
            Virtual Machine Identifier. A vmid takes the following form:
                       [@[:]]
                  Where  is the local vm identifier for the target
                  Java virtual machine, typically a process id;  is
                  the name of the host running the target Java virtual machine;
                  and  is the port number for the rmiregistry on the
                  target host. See the jvmstat documentation for a more complete
                  description of the Virtual Machine Identifier.
           Number of samples between header lines.
        Sampling interval. The following forms are allowed:
                      ["ms"|"s"]
                  Where  is an integer and the suffix specifies the units as 
                  milliseconds("ms") or seconds("s"). The default units are "ms".
           Number of samples to take before terminating.
    -J      Pass  directly to the runtime system.
  

• jstat -options

  root@CN02:/home/demo-server# jstat -options
  -class
  -compiler
  -gc
  -gccapacity
  -gccause
  -gcmetacapacity
  -gcnew
  -gcnewcapacity
  -gcold
  -gcoldcapacity
  -gcutil
  -printcompilation
  

• jstat -gcutil [ []]

  root@CN02:/home/demo-server# jstat -gcutil 15509 1000 5
    S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT   
    0.00   0.00   1.73  14.61  92.80  90.76     16    1.117     9    0.888    2.006
    0.00   0.00   1.73  14.61  92.80  90.76     16    1.117     9    0.888    2.006
    0.00   0.00   1.73  14.61  92.80  90.76     16    1.117     9    0.888    2.006
    0.00   0.00   1.73  14.61  92.80  90.76     16    1.117     9    0.888    2.006
    0.00   0.00   1.73  14.61  92.80  90.76     16    1.117     9    0.888    2.006
  

Jmap常用命令（Memory Map）

• jmap -help

  root@CN02:/home/demo-server# jmap -help
  Usage:
      jmap [option] 
          (to connect to running process)
      jmap [option] 
          (to connect to a core file)
      jmap [option] [server_id@]
          (to connect to remote debug server)
  
  where  is one of:
                     to print same info as Solaris pmap
      -heap                to print java heap summary
      -histo[:live]        to print histogram of java object heap; if the "live"
                           suboption is specified, only count live objects
      -clstats             to print class loader statistics
      -finalizerinfo       to print information on objects awaiting finalization
      -dump: to dump java heap in hprof binary format
                           dump-options:
                             live         dump only live objects; if not specified,
                                          all objects in the heap are dumped.
                             format=b     binary format
                             file=  dump heap to 
                           Example: jmap -dump:live,format=b,file=heap.bin 
      -F                   force. Use with -dump:  or -histo
                           to force a heap dump or histogram when  does not
                           respond. The "live" suboption is not supported
                           in this mode.
      -h | -help           to print this help message
      -J             to pass  directly to the runtime system
  

• jmap -histo:live | more

  root@CN02:/home/demo-server# jmap -histo:live 15509 | more
  
   num     #instances         #bytes  class name
  ----------------------------------------------
     1:        112649       10985672  [C
     2:         31705        2790040  java.lang.reflect.Method
     3:        112092        2690208  java.lang.String
     4:         73094        2339008  java.util.concurrent.ConcurrentHashMap$Node
     5:         17300        1911192  java.lang.Class
     6:         26357        1535776  [Ljava.lang.Object;
     7:          6531        1173184  [B
     8:          8364        1068264  [I
     9:         25101        1004040  java.util.LinkedHashMap$Entry
    10:          9878         804744  [Ljava.util.HashMap$Node;
    11:         39438         631008  java.lang.Object
    12:         18762         600384  java.util.HashMap$Node
    13:           278         595344  [Ljava.util.concurrent.ConcurrentHashMap$Node;
    14:         10367         580552  java.util.LinkedHashMap
  

  class name列是对象类型，说明如下：

  B  byte
  C  char
  D  double
  F  float
  I  int
  J  long
  Z  boolean
  [  数组，如[I表示int[]
  [L+类名 其他对象
  

• jmap -dump:live,format=b,file=heap.bin

  root@CN02:/home/demo-server# jmap -dump:live,format=b,file=heap.bin 15509
  Dumping heap to /home/demo-server/heap.bin ...
  Heap dump file created
  

  dump出来的文件可以用jhat命令、MAT、VisualVM等工具查看。

Jhat常用命令（Java Heap Analysis Tool）

• jhat -help

  root@CN02:/home/demo-server# jhat -help
  Usage:  jhat [-stack ] [-refs ] [-port ] [-baseline ] [-debug ] [-version] [-h|-help] 
  
          -J          Pass  directly to the runtime system. For
                            example, -J-mx512m to use a maximum heap size of 512MB
          -stack false:     Turn off tracking object allocation call stack.
          -refs false:      Turn off tracking of references to objects
          -port :     Set the port for the HTTP server.  Defaults to 7000
          -exclude :  Specify a file that lists data members that should
                            be excluded from the reachableFrom query.
          -baseline : Specify a baseline object dump.  Objects in
                            both heap dumps with the same ID and same class will
                            be marked as not being "new".
          -debug :     Set debug level.
                              0:  No debug output
                              1:  Debug hprof file parsing
                              2:  Debug hprof file parsing, no server
          -version          Report version number
          -h|-help          Print this help and exit
                      The file to read
  
  For a dump file that contains multiple heap dumps,
  you may specify which dump in the file
  by appending "#" to the file name, i.e. "foo.hprof#3".
  
  All boolean options default to "true"
  

• jhat -J-Xmx512m heap.bin

  root@CN02:/home/demo-server# jhat -J-Xmx512m heap.bin
  Reading from heap.bin...
  Dump file created Tue Jun 25 01:53:08 CST 2022
  Snapshot read, resolving...
  Resolving 2779596 objects...
  Chasing references, expect 555 dots................................................................................................................
  ...................................................................................................................................................
  ...................................................................................................................................................
  ...................................................................................................................................................
  ..
  Eliminating duplicate references...................................................................................................................
  ...................................................................................................................................................
  ...................................................................................................................................................
  ..................................................................................................................................................
  Snapshot resolved.
  Started HTTP server on port 7000
  Server is ready.
  

  浏览器访问：http://localhost:7000
  

Jstack常用命令

• jstack -help

  root@CN02:/home/demo-server# jstack -help
  Usage:
      jstack [-l] 
          (to connect to running process)
      jstack -F [-m] [-l] 
          (to connect to a hung process)
      jstack [-m] [-l]  
          (to connect to a core file)
      jstack [-m] [-l] [server_id@]
          (to connect to a remote debug server)
  
  Options:
      -F  to force a thread dump. Use when jstack  does not respond (process is hung)
      -m  to print both java and native frames (mixed mode)
      -l  long listing. Prints additional information about locks
      -h or -help to print this help message
  

Jinfo常用命令

• jinfo -help

  root@CN02:/home/demo-server# jinfo -help
  Usage:
      jinfo [option] 
          (to connect to running process)
      jinfo [option] 
          (to connect to a core file)
      jinfo [option] [server_id@]
          (to connect to remote debug server)
  
  where  is one of:
      -flag          to print the value of the named VM flag
      -flag [+|-]    to enable or disable the named VM flag
      -flag = to set the named VM flag to the given value
      -flags               to print VM flags
      -sysprops            to print Java system properties
                to print both of the above
      -h | -help           to print this help message
  

Jcmd常用命令

• jcmd -help

  root@CN02:/home/demo-server# jcmd -help
  Usage: jcmd  
     or: jcmd -l                                                    
     or: jcmd -h                                                    
                                                                    
    command must be a valid jcmd command for the selected jvm.      
    Use the command "help" to see which commands are available.   
    If the pid is 0, commands will be sent to all Java processes.   
    The main class argument will be used to match (either partially 
    or fully) the class used to start Java.                         
    If no options are given, lists Java processes (same as -p).     
                                                                    
    PerfCounter.print display the counters exposed by this process  
    -f  read and execute commands from the file                     
    -l  list JVM processes on the local machine                     
    -h  this help
  

• jcmd -l

  root@CN02:/home/demo-server# jcmd -l
  16082 demo-uat.jar --spring.profiles.active=uat
  16420 sun.tools.jcmd.JCmd -l
  15509 demo-test.jar --spring.profiles.active=test
  

• jcmd help

  root@CN02:/home/demo-server# jcmd 15509 help
  15509:
  The following commands are available:
  VM.unlock_commercial_features
  JFR.configure
  JFR.stop
  JFR.start
  JFR.dump
  JFR.check
  VM.native_memory
  ManagementAgent.stop
  ManagementAgent.start_local
  ManagementAgent.start
  VM.classloader_stats
  GC.rotate_log
  Thread.print
  GC.class_stats
  GC.class_histogram
  GC.heap_dump
  GC.finalizer_info
  GC.heap_info
  GC.run_finalization
  GC.run
  VM.uptime
  VM.dynlibs
  VM.flags
  VM.system_properties
  VM.command_line
  VM.version
  help
  
  For more information about a specific command use 'help '.
  

• jcmd GC.heap_info

  root@CN02:/home/demo-server# jcmd 15509 GC.heap_info
  15509:
   par new generation   total 471872K, used 22827K [0x00000000d0000000, 0x00000000f0000000, 0x00000000f0000000)
    eden space 419456K,   5% used [0x00000000d0000000, 0x00000000d164ae48, 0x00000000e99a0000)
    from space 52416K,   0% used [0x00000000e99a0000, 0x00000000e99a0000, 0x00000000eccd0000)
    to   space 52416K,   0% used [0x00000000eccd0000, 0x00000000eccd0000, 0x00000000f0000000)
   concurrent mark-sweep generation total 262144K, used 38326K [0x00000000f0000000, 0x0000000100000000, 0x0000000100000000)
   Metaspace       used 86305K, capacity 92137K, committed 92944K, reserved 1130496K
    class space    used 10985K, capacity 11915K, committed 12100K, reserved 1048576K
  

Jconsole工具详解 Jvisualvm工具详解

https://github.com/oracle/visualvm

VisualVM is an All-in-One Java Troubleshooting Tool

MAT工具详解（Memory Analyzer Tool）

http://www.eclipse.org/mat/downloads.php

Arthas工具详解

源码：https://github.com/alibaba/arthas
官网：https://arthas.aliyun.com/zh-cn/

GC日志分析 GCEasy日志分析工具使用

https://www.gceasy.io/

Universal
GC Log Analyzer
Industry’s first machine learning guided Garbage collection log analysis tool. GCeasy has in-built intelligence to auto-detect problems in the JVM & Android GC logs and recommend solutions to it.

• Solve Memory & GC problems in seconds
• Get JVM Heap settings recommendations
• Machine Learning Algorithms
• Trusted by 4,000+ enterprises

GCViewer日志分析工具使用

https://github.com/chewiebug/GCViewer

Fork of tagtraum industries’ GCViewer. Tagtraum stopped development in 2008, I aim to improve support for Sun’s / Oracle’s java 1.6+ garbage collector logs (including G1 collector)

调优实战

• 了解JDK版本信息？

  OpenJDK还是OracleJDK，JDK6、JDK8还是JDK11等等，第一时间掌握不同版本对JVM调优方式的差异。
  

• 了解服务器内存、CPU及磁盘空间等信息？

  掌握对JVM可分配的物理内存大小
  

• 了解服务的业务类型？

  根据服务的内存使用特点选择更适合的垃圾收集器
  

• 了解服务访问流量？

  分析单位时间内年轻代、老年代内存变化曲线
  

• 了解服务启动命令？

  掌握内存分配、GC垃圾收集器等情况
  

• 是否有近期的GC日志？

  分析系统当前JVM Throughput、FGC等指标，用于调优后进行指标对比。
  

亿级电商网站 jvm 参数调优实战案例

java -Xms3g -Xmx3g -Xmn2g -Xss1M -XX:MetaspaceSize=512M -XX:MaxmetaspaceSize=512M -jar order.jar

单机几十万并发的系统 jvm 如何优化

如：RocktMQ、Kafuka

java -Xms64g -Xmx64g -Xss1M -XX:+UseG1GC -XX:MaxGCPauseMillis=100 
-XX:MetaspaceSize=512M -XX:MaxmetaspaceSize=512M -jar RocktMQ.jar

参考

• 5 款强大的 JVM 性能调优工具 ，好用爆了
• JVM性能调优工具2之jcmd详解（覆盖全网最全的jcmd命令与说明文档）
• 【Java线程与内存分析工具】VisualVM与MAT简明教程