关于java:JAVA基础之虚拟机故障处理工具

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明天学习了《深刻了解 java 虚拟机》的故障解决工具，都是一些小命令，不简单，只不过有些命令在 prod 环境不要应用，jmap 这种，在动辄几 G 的内存的 pod 中，生成一次文件可能就导致了环境进行，这时如果还有大量申请进来，这个 pod 预计在生成 dump 文件之前就解体了。

jps 命令查看 java 过程

buxuesongdeMacBook-Pro:~ buxuesong$ jps -l
1121 /Users/buxuesong/Documents/git_code/account/account-api/target/account-api-1.3.0-SNAPSHOT.jar
1131 sun.tools.jps.Jps
buxuesongdeMacBook-Pro:~ buxuesong$ ps -ef|grep 1121
  501  1121  1120   0 11:01 下午 ttys000    0:24.41 /usr/bin/java -jar /Users/buxuesong/Documents/git_code/account/account-api/target/account-api-1.3.0-SNAPSHOT.jar
  501  1138  1125   0 11:02 下午 ttys001    0:00.00 grep 1121
buxuesongdeMacBook-Pro:~ buxuesong$

jstat 命令用于监督虚拟机各种运行状态信息

buxuesongdeMacBook-Pro:~ buxuesong$ jstat -gcutil 1121
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT   
  0.00  96.78  63.52  23.52  95.12  92.69     11    0.101     2    0.211    0.311
  //1121 命令下，2 个 Survivor 区（S0、S1，示意 Survivor0、Survivor1）,S0 为空，S1 占用 96.78%，新生代 Eden 区（E，示意 Eden）应用了 63.52%
  // 老年代（O，示意 Old）和永恒代（M）则别离应用了 23.52% 和 95.12% 的空间
  //CCS，压缩应用比例 92.69%
  // 程序运行以来共产生 Minor GC（YGC，示意 Young GC）11 次，总耗时 0.101 秒；// 产生 Full GC（FGC，示意 Full GC）2 次，总耗时（FGCT，示意 Full GCTime）为 0.211 秒；所有 GC 总耗时（GCT，示意 GC Time）为 0.311 秒。

jinfo 命令实时查看和调整虚拟机各项参数

buxuesongdeMacBook-Pro:~ buxuesong$ jinfo -flag CMSInitiatingOccupancyFraction 1835
-XX:CMSInitiatingOccupancyFraction=-1

jmap（Memory Map for Java）命令用于生成堆转储快照（个别称为 heapdump 或 dump 文件）

buxuesongdeMacBook-Pro:~ buxuesong$ jmap -dump:format=b,file=account.dump 1868
Dumping heap to /Users/buxuesong/account.dump ...
Heap dump file created

jhat（JVM Heap Analysis Tool）命令与 jmap 搭配应用，来剖析 jmap 生成的堆转储快照。运行结束后通过 http://localhost:7000 来拜访查看 dump 内容

buxuesongdeMacBook-Pro:~ buxuesong$ jhat account.dump 
Reading from account.dump...
Dump file created Wed Nov 25 23:37:23 CST 2020
Snapshot read, resolving...
Resolving 402521 objects...
Chasing references, expect 80 dots................................................................................
Eliminating duplicate references................................................................................
Snapshot resolved.
Started HTTP server on port 7000
Server is ready.

jstack（Stack Trace for Java）命令用于生成虚拟机以后时刻的线程快照（个别称为 threaddump 或者 javacore 文件）

buxuesongdeMacBook-Pro:~ buxuesong$ jstack -l 1939
2020-11-25 23:47:43
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.201-b09 mixed mode):

"Attach Listener" #34 daemon prio=9 os_prio=31 tid=0x00007fbe7a496800 nid=0x9d03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
    - None

"Druid-ConnectionPool-Destroy-205735257" #33 daemon prio=5 os_prio=31 tid=0x00007fbe77f6f800 nid=0x9f03 waiting on condition [0x0000700012133000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at com.alibaba.druid.pool.DruidDataSource$DestroyConnectionThread.run(DruidDataSource.java:2032)

   Locked ownable synchronizers:
    - None

"Druid-ConnectionPool-Create-205735257" #32 daemon prio=5 os_prio=31 tid=0x00007fbe77a01800 nid=0xa003 waiting on condition [0x0000700012030000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000007aa5174d0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:1948)

   Locked ownable synchronizers:
    - None

"mysql-cj-abandoned-connection-cleanup" #31 daemon prio=5 os_prio=31 tid=0x00007fbe7a3cf000 nid=0x6703 in Object.wait() [0x0000700011f2d000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x0000000797d2a1f0> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
    - locked <0x0000000797d2a1f0> (a java.lang.ref.ReferenceQueue$Lock)
    at com.mysql.cj.jdbc.AbandonedConnectionCleanupThread.run(AbandonedConnectionCleanupThread.java:85)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
    - <0x0000000797d2cce0> (a java.util.concurrent.ThreadPoolExecutor$Worker)

"DestroyJavaVM" #30 prio=5 os_prio=31 tid=0x00007fbe7c87f800 nid=0x1003 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
    - None

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