Java 性能分析工具介绍

JDK 提供了很多 JVM 性能调优监控工具，包括jps、jstack、jmap、jhat、jstat、hprof等，用户可以检测 Java 应用或者程序片段的状况。

总揽

命令	作用
jps	基础工具
jstack	查看某个Java进程内的线程堆栈信息
jmap	jmap导出堆内存，然后使用jhat来进行分析
jhat	jmap导出堆内存，然后使用jhat来进行分析
jstat	JVM统计监测工具
hprof	hprof能够展现CPU使用率，统计堆内存使用情况

导出 HeapDump 文件

• 内存 OOM 时导出

java -jar -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp/heap.hprof <server>.jar

jps

jps主要用来输出JVM中运行的进程状态信息，实际中这是最常用的命令，下面要介绍的小工具更多的都是先要使用jps查看出当前有哪些Java进程，获取该Java进程的id后再对该进程进行处理。

[root@xiexianbin_cn ~]# jps -help
usage: jps [-help]
       jps [-q] [-mlvV] [<hostid>]

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

说明：

• -q: 只显示VM 标示，不显示jar,class, main参数等信息。
• -m: 输出主函数传入的参数。
• -l: 输出应用程序主类完整package名称或jar完整名称。
• -v: 列出jvm启动参数。
• -V: 输出通过.hotsportrc或-XX:Flags=指定的jvm参数。
• -Joption: 传递参数到javac 调用的java lancher。

jstack

jstack用于生成java虚拟机当前时刻的线程快照。jstack命令主要用来查看Java线程的调用堆栈的，可以用来分析线程问题。

线程的几种状态：

• NEW,未启动的。不会出现在Dump中。
• RUNNABLE,在虚拟机内执行的。
• BLOCKED,受阻塞并等待监视器锁。
• WATING,无限期等待另一个线程执行特定操作。
• TIMED_WATING,有时限的等待另一个线程的特定操作。
• TERMINATED,已退出的。

使用：

[root@xiexianbin_cn ~]# 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

jstack -l pid

jmap

jmap是JDK自带的工具软件，主要用于打印指定Java进程(或核心文件、远程调试服务器)的共享对象内存映射或堆内存细节。可以使用jmap生成Heap Dump。

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

运行时导出 heap

• 运行时导出 heap 文件，示例

jmap -dump:live,format=b,file=heap.hprof <pid>

jhat

jhat命令解析会Java堆dump并启动一个web服务器，然后就可以在浏览器中查看堆的dump文件了

[root@xiexianbin_cn ~]# 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"

jstat

jstat(JVM Statistics Monitoring Tool)是用于监控虚拟机各种运行状态信息的命令行工具。他可以显示本地或远程虚拟机进程中的类装载、内存、垃圾收集、JIT编译等运行数据，在没有GUI图形的服务器上，它是运行期定位虚拟机性能问题的首选工具。

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.

jar xvf

• jinfo

产生 OOM 的原因

• java.lang.OutOfMemoryError 产生原因是因为内存不够，可以通过增加 Xmx 避免该现象
• Java 容器 OOM Killed 产生原因是因为 堆外内存 + 堆内存 总体超出限制 limit.request 导致的容器 Kill 行为，该行为不会产生 heapdump 文件
  • 参考