【JVM系列】JVM调优

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

Definitions:
    <hostid>:      <hostname>[:<port>]

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

root@CN02:/home/demo-server# jstat -help
Usage: jstat -help|-options
       jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]

Definitions:
  <option>      An option reported by the -options option
  <vmid>        Virtual Machine Identifier. A vmid takes the following form:
                     <lvmid>[@<hostname>[:<port>]]
                Where <lvmid> is the local vm identifier for the target
                Java virtual machine, typically a process id; <hostname> is
                the name of the host running the target Java virtual machine;
                and <port> 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.
  <lines>       Number of samples between header lines.
  <interval>    Sampling interval. The following forms are allowed:
                    <n>["ms"|"s"]
                Where <n> is an integer and the suffix specifies the units as 
                milliseconds("ms") or seconds("s"). The default units are "ms".
  <count>       Number of samples to take before terminating.
  -J<flag>      Pass <flag> directly to the runtime system.

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

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

root@CN02:/home/demo-server# jmap -help
Usage:
    jmap [option] <pid>
        (to connect to running process)
    jmap [option] <executable <core>
        (to connect to a core file)
    jmap [option] [server_id@]<remote server IP or hostname>
        (to connect to remote debug server)

where <option> is one of:
    <none>               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:<dump-options> 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=<file>  dump heap to <file>
                         Example: jmap -dump:live,format=b,file=heap.bin <pid>
    -F                   force. Use with -dump:<dump-options> <pid> or -histo
                         to force a heap dump or histogram when <pid> does not
                         respond. The "live" suboption is not supported
                         in this mode.
    -h | -help           to print this help message
    -J<flag>             to pass <flag> directly to the runtime system

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

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

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

root@CN02:/home/demo-server# jhat -help
Usage:  jhat [-stack <bool>] [-refs <bool>] [-port <port>] [-baseline <file>] [-debug <int>] [-version] [-h|-help] <file>

        -J<flag>          Pass <flag> 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 <port>:     Set the port for the HTTP server.  Defaults to 7000
        -exclude <file>:  Specify a file that lists data members that should
                          be excluded from the reachableFrom query.
        -baseline <file>: 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 <int>:     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
        <file>            The file to read

For a dump file that contains multiple heap dumps,
you may specify which dump in the file
by appending "#<number>" to the file name, i.e. "foo.hprof#3".

All boolean options default to "true"

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.

root@CN02:/home/demo-server# jstack -help
Usage:
    jstack [-l] <pid>
        (to connect to running process)
    jstack -F [-m] [-l] <pid>
        (to connect to a hung process)
    jstack [-m] [-l] <executable> <core>
        (to connect to a core file)
    jstack [-m] [-l] [server_id@]<remote server IP or hostname>
        (to connect to a remote debug server)

Options:
    -F  to force a thread dump. Use when jstack <pid> 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

root@CN02:/home/demo-server# jinfo -help
Usage:
    jinfo [option] <pid>
        (to connect to running process)
    jinfo [option] <executable <core>
        (to connect to a core file)
    jinfo [option] [server_id@]<remote server IP or hostname>
        (to connect to remote debug server)

where <option> is one of:
    -flag <name>         to print the value of the named VM flag
    -flag [+|-]<name>    to enable or disable the named VM flag
    -flag <name>=<value> to set the named VM flag to the given value
    -flags               to print VM flags
    -sysprops            to print Java system properties
    <no option>          to print both of the above
    -h | -help           to print this help message

root@CN02:/home/demo-server# jcmd -help
Usage: jcmd <pid | main class> <command ...|PerfCounter.print|-f file>
   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

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

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 <command>'.

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

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。

掌握对JVM可分配的物理内存大小

根据服务的内存使用特点选择更适合的垃圾收集器

分析单位时间内年轻代、老年代内存变化曲线

掌握内存分配、GC垃圾收集器等情况

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

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

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