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 -l1121 /Users/buxuesong/Documents/git_code/account/account-api/target/account-api-1.3.0-SNAPSHOT.jar1131 sun.tools.jps.JpsbuxuesongdeMacBook-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 1121buxuesongdeMacBook-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 1868Dumping 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 2020Snapshot read, resolving...Resolving 402521 objects...Chasing references, expect 80 dots................................................................................Eliminating duplicate references................................................................................Snapshot resolved.Started HTTP server on port 7000Server 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 19392020-11-25 23:47:43Full 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