jvm 性能调优工具之 jstat

太过爱你忘了你带给我的痛 2022-11-14 11:56 249阅读 0赞

# jstat介绍 #

Monitors Java Virtual Machine (JVM) statistics.

官网文档： https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstat.html

# jstat 用法 #

# 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.

## 统计gc情况 ##

jstat -gc java进程ID

# jstat -gc 19567
     S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT   
    5120.0 5120.0 3734.0  0.0   338944.0 149348.4  699392.0   87674.3   105624.0 99251.1 11952.0 10845.5   1180   17.213   5      1.359   18.572

参数介绍：

> S0C：第一个幸存区的大小  
> S1C：第二个幸存区的大小  
> S0U：第一个幸存区的使用大小  
> S1U：第二个幸存区的使用大小  
> EC：伊甸园区的大小  
> EU：伊甸园区的使用大小  
> OC：老年代大小  
> OU：老年代使用大小  
> MC：方法区大小  
> MU：方法区使用大小  
> CCSC:压缩类空间大小  
> CCSU:压缩类空间使用大小  
> YGC：年轻代垃圾回收次数  
> YGCT：年轻代垃圾回收消耗时间  
> FGC：老年代垃圾回收次数  
> FGCT：老年代垃圾回收消耗时间  
> GCT：垃圾回收消耗总时间

## 计算GC频率 ##

1.  查看java进程运行时间(系统运行时间与进程启动之间之差)

ps -eo pid,tty,user,comm,lstart,etime | grep java进程ID

# ps -eo pid,tty,user,comm,lstart,etime | grep 19567
    19567 ?        root     java            Fri Mar 12 17:48:21 2021 16-17:28:47

代表已启动16天17小时28份47秒

1.  计算频率  
    16-17:28:47 换算成分钟除以YGC或者FGC 就可以得出频率了

# 当前gc情况 #

jstat -gcutil pid time

示例，每秒钟查看当前gc情况

# jstat -gcutil 13798 1000
      S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT   
      0.00  96.98  20.00  10.46  94.03  90.71     27    0.312     4    0.712    1.024
      0.00  96.98  20.00  10.46  94.03  90.71     27    0.312     4    0.712    1.024
      0.00  96.98  20.00  10.46  94.03  90.71     27    0.312     4    0.712    1.024
      0.00  96.98  20.00  10.46  94.03  90.71     27    0.312     4    0.712    1.024
      0.00  96.98  20.01  10.46  94.03  90.71     27    0.312     4    0.712    1.024
      0.00  96.98  20.01  10.46  94.03  90.71     27    0.312     4    0.712    1.024

参数介绍

> \-gcutil option  
> Summary of garbage collection statistics.  
> S0: Survivor space 0 utilization as a percentage of the space’s current capacity.  
> S1: Survivor space 1 utilization as a percentage of the space’s current capacity.  
> E: Eden space utilization as a percentage of the space’s current capacity.  
> O: Old space utilization as a percentage of the space’s current capacity.  
> M: Metaspace utilization as a percentage of the space’s current capacity.  
> CCS: Compressed class space utilization as a percentage.  
> YGC: Number of young generation GC events.  
> YGCT: Young generation garbage collection time.  
> FGC: Number of full GC events.  
> FGCT: Full garbage collection time.  
> GCT: Total garbage collection time.

还有其他用法，可在文档中查找