JVM中jstat命令和jmap命令_jmap -histo pid

jstat(Java Virtual Machine Statistics Monitoring Tool) 用于监视虚拟机各种运行状态信息的命令行工具.可以显示虚拟机的类装载,内存,垃圾收集,JIT编译等运行数据.

远程命令模式下jstat是定位运行期JVM性能问题的首选工具.本地首选VisualVM.

使用方式可以参考官方文档.

jstat -gc <pid>: 可以显示gc的信息，查看gc的次数，及时间。

C:\Users\rongsoft>jstat -gc 2092
 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT
10752.0 10752.0  0.0    0.0   65536.0  29375.9   108032.0   21582.5   21248.0 20674.5 2560.0 2382.2      2    0.017  1      0.025

  0.042

列成表格是像下面这样:

如果需要打印内存日志,需要增加参数:
-XX:+PrintGCDetails -XX:-UseAdaptiveSizePolicy -XX:SurvivorRatio=8 -XX:NewSize=10M -XX:MaxNewSize=10M

ps -ef |grep xxxxxx.jar

java -Xmx2048M -Xms512M -Djeesuite.configcenter.profile=pro -Djava.io.tmpdir=/home/server/microservice/xxxxx/temp/ -jar /home/server/microservice/xxxxx.jar

-XX:-UseAdaptiveSizePolicy 禁用动态调整，使SurvivorRatio可以起作用

-XX:SurvivorRatio=8 设置比例Eden:Survivior=8,那么2个Survivior区就是2.

jmap命令:可以查看堆默认配置信息

 jmap -heap 995

[root@service-docker-192-168-1-91.workflow]# jmap -heap 995
Attaching to process ID 995, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14
 
using thread-local object allocation.
Parallel GC with 8 thread(s)
 
Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 1073741824 (1024.0MB)
   NewSize                  = 178782208 (170.5MB)
   MaxNewSize               = 357564416 (341.0MB)
   OldSize                  = 358088704 (341.5MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)
 
Heap Usage:
PS Young Generation
Eden Space:
   capacity = 252182528 (240.5MB)
   used     = 184114440 (175.58521270751953MB)
   free     = 68068088 (64.91478729248047MB)
   73.00840445219107% used
From Space:
   capacity = 7864320 (7.5MB)
   used     = 7864320 (7.5MB)
   free     = 0 (0.0MB)
   100.0% used
To Space:
   capacity = 15728640 (15.0MB)
   used     = 0 (0.0MB)
   free     = 15728640 (15.0MB)
   0.0% used
PS Old Generation
   capacity = 358088704 (341.5MB)
   used     = 317911272 (303.1838150024414MB)
   free     = 40177432 (38.316184997558594MB)
   88.7800336756783% used
 
34539 interned Strings occupying 4082072 bytes.

关于JVM得参数配置,可以参考官网https://docs.oracle.com/javase/9/gctuning/toc.htm

第四节 4 Factors Affecting Garbage Collection Performance

其中Virtual区是供新生代和老年代使用的.堆总大小为 Eden,survivor,survivor,Old.

Table 4-1 Default Options for 64-Bit Solaris Operating System

The Young Generation

After total available memory, the second most influential factor affecting garbage collection performance is the proportion of the heap dedicated to the young generation.

The bigger the young generation, the less often minor collections occur. However, for a bounded heap size, a larger young generation implies a smaller old generation, which will increase the frequency of major collections. The optimal choice depends on the lifetime distribution of the objects allocated by the application.

Young Generation Size Options

By default, the young generation size is controlled by the option -XX:NewRatio.

For example, setting -XX:NewRatio=3 means that the ratio between the young and old generation is 1:3. In other words, the combined size of the eden and survivor spaces will be one-fourth of the total heap size.

The options -XX:NewSize and -XX:MaxNewSize bound the young generation size from below and above. Setting these to the same value fixes the young generation, just as setting -Xms and -Xmx to the same value fixes the total heap size. This is useful for tuning the young generation at a finer granularity than the integral multiples allowed by -XX:NewRatio.

Survivor Space Sizing

You can use the option -XX:SurvivorRatio to tune the size of the survivor spaces, but often this isn't important for performance.

For example, -XX:SurvivorRatio=6 sets the ratio between eden and a survivor space to 1:6. In other words, each survivor space will be one-sixth of the size of eden, and thus one-eighth of the size of the young generation (not one-seventh, because there are two survivor spaces).

If survivor spaces are too small, then the copying collection overflows directly into the old generation. If survivor spaces are too large, then they are uselessly empty. At each garbage collection, the virtual machine chooses a threshold number, which is the number of times an object can be copied before it's old. This threshold is chosen to keep the survivors half full. You can use the log configuration -Xlog:gc,age can be used to show this threshold and the ages of objects in the new generation. It's also useful for observing the lifetime distribution of an application.

Table 4-2 provides the default values for 64-bit Solaris.

Table 4-2 Default Option Values for Survivor Space Sizing

The maximum size of the young generation is calculated from the maximum size of the total heap and the value of the -XX:NewRatio parameter. The "not limited" default value for the -XX:MaxNewSize parameter means that the calculated value isn't limited by -XX:MaxNewSize unless a value for -XX:MaxNewSize is specified on the command line.

jstat查看容量大小:

jstat -gccapacity 31209

[root@web-nginx-192-168-1-92.test92.ayg logs]# jstat -gccapacity 31209
 NGCMN    NGCMX     NGC     S0C   S1C       EC      OGCMN      OGCMX       OGC         OC       MCMN     MCMX      MC     CCSMN    CCSMX     CCSC    YGC    FGC 
 87040.0 174592.0 100352.0 2560.0 4608.0  79872.0   175104.0   349696.0   326656.0   326656.0      0.0 1165312.0 131624.0      0.0 1048576.0  14896.0   9779    12

• NGCMN：年轻代(young)中初始化(最小)的大小(字节)
• NGCMX：年轻代(young)的最大容量 (字节)
• NGC：年轻代(young)中当前的容量 (字节)
• S0C：年轻代中第一个survivor（幸存区）的容量 (字节)
• S1C：年轻代中第二个survivor（幸存区）的容量 (字节)
• EC：年轻代中Eden（伊甸园）的容量 (字节)
• OGCMN：old代中初始化(最小)的大小 (字节)
• OGCMX：old代的最大容量(字节)
• OGC：old代当前新生成的容量 (字节)
• OC：Old代的容量 (字节)
• MCMN：metaspace(元空间)中初始化(最小)的大小 (字节)
• MCMX：metaspace(元空间)的最大容量 (字节)
• MC：metaspace(元空间)当前新生成的容量 (字节)
• CCSMN：最小压缩类空间大小
• CCSMX：最大压缩类空间大小
• CCSC：当前压缩类空间大小
• YGC：从应用程序启动到采样时年轻代中gc次数
• FGC：从应用程序启动到采样时old代(全gc)gc次数

jstat使用举例:详细可以参考jvm 性能调优工具之 jstat 命令详解

[root@web-nginx-192-168-1-92 logs]# jps
9348 springcloud-apigateway.jar
18117 Bootstrap
5542 Bootstrap
3880 QuorumPeerMain
31209 mypayer.jar
5322 Bootstrap
4748 springcloud-admin.jar
5709 Bootstrap
4470 configserver.jar
7734 ConsoleConsumer
12822 Jps
20375 Bootstrap
8122 ConnectStandalone
4347 Kafka
4699 springcloud-eureka.jar
You have new mail in /var/spool/mail/root
[root@web-nginx-192-168-1-92 logs]# jstat -gccapacity 31209
 NGCMN    NGCMX     NGC     S0C   S1C       EC      OGCMN      OGCMX       OGC         OC       MCMN     MCMX      MC     CCSMN    CCSMX     CCSC    YGC    FGC 
 87040.0 174592.0 100352.0 2560.0 4608.0  79872.0   175104.0   349696.0   326656.0   326656.0      0.0 1165312.0 131624.0      0.0 1048576.0  14896.0   9779    12
[root@web-nginx-192-168-1-92 logs]# jstat -gcold 31209
   MC       MU      CCSC     CCSU       OC          OU       YGC    FGC    FGCT     GCT   
131624.0 126963.1  14896.0  13916.6    326656.0    130010.1   9813    12    4.207  190.493
[root@web-nginx-192-168-1-92 logs]# jstat -gcnew 31209
 S0C    S1C    S0U    S1U   TT MTT  DSS      EC       EU     YGC     YGCT  
3072.0 3072.0 2064.0    0.0  1  15 3072.0 168448.0 109317.2  14998  273.159
You have new mail in /var/spool/mail/root
[root@web-nginx-192-168-1-92 logs]# jstat -gcoldcapacity 31209
   OGCMN       OGCMX        OGC         OC       YGC   FGC    FGCT     GCT   
   175104.0    349696.0    288768.0    288768.0 15002    17    6.059  279.273
[root@web-nginx-192-168-1-92 logs]# jstat -gcnewcapacity 31209
  NGCMN      NGCMX       NGC      S0CMX     S0C     S1CMX     S1C       ECMX        EC      YGC   FGC 
   87040.0   174592.0   168448.0  57856.0   3072.0  57856.0   2048.0   173568.0   151552.0 15003    17
[root@web-nginx-192-168-1-92 logs]# jstat -gcutil 31209
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT   
 99.22   0.00  11.10  56.16  96.39  93.46  15028  273.592    17    6.059  279.651

如果要打印GC日志,可以增加配置参数

-XX:+PrintGC 输出GC日志
-XX:+PrintGCDetails 输出GC的详细日志(jdk9已经废弃)
-XX:+PrintGCTimeStamps 输出GC的时间戳（以基准时间的形式）
-XX:+PrintGCDateStamps 输出GC的时间戳（jdk9已经移除.以日期的形式，如 2013-05-04T21:53:59.234+0800）
-XX:+PrintHeapAtGC 在进行GC的前后打印出堆的信息
-Xloggc:../logs/gc.log 日志文件的输出路径

 注意:已经废弃的参数配置后可能导致启动失败.

jmap导出文件

jmap -dump:format=b,live,file=jmap.dump 31209

参考:

用jvisualvm分析dump文件

jstack检测cpu高