Jmap
查询堆信息 ：jmap -heap pid
C:\Users\41732>jmap -heap 9780 Attaching to process ID 9780, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.152-b16 using thread-local object allocation. Parallel GC with 4 thread(s) Heap Configuration: MinHeapFreeRatio = 0 MaxHeapFreeRatio = 100 MaxHeapSize = 4267704320 (4070.0M NewSize = 89128960 (85.0MB) MaxNewSize = 1422393344 (1356.5M OldSize = 179306496 (171.0MB) NewRatio = 2 SurvivorRatio = 8 MetaspaceSize = 21807104 (20.796875 CompressedClassSpaceSize = 1073741824 (1024.0M MaxMetaspaceSize = 17592186044415 MB G1HeapRegionSize = 0 (0.0MB) Heap Usage: PS Young Generation Eden Space: capacity = 65536000 (62.5MB) used = 36124952 (34.451438903808594MB) free = 29411048 (28.048561096191406MB) 55.12230224609375% used From Space: capacity = 14680064 (14.0MB) used = 4598376 (4.385353088378906MB) free = 10081688 (9.614646911621094MB) 31.323950631277903% used To Space: capacity = 14680064 (14.0MB) used = 0 (0.0MB) free = 14680064 (14.0MB) 0.0% used PS Old Generation capacity = 110100480 (105.0MB) used = 13078136 (12.472282409667969MB) free = 97022344 (92.52771759033203MB) 11.87836419968378% used 15044 interned Strings occupying 2001648 bytes.
查看当前实例个数：jmap -histo pid
num #instances #bytes class name ---------------------------------------------- 1: 123030 17393624 [C 2: 42214 13424608 [B 3: 10861 4126040 [I 4: 23535 2071080 java.lang.reflect.Method 5: 70927 1702248 java.lang.String 6: 22263 1075592 [Ljava.lang.Object; 7: 37505 779912 [Ljava.lang.Class; 8: 7161 629160 [Ljava.util.HashMap$Node; 9: 12558 602784 java.util.HashMap 10: 5286 592496 java.lang.Class 11: 16836 538752 java.util.HashMap$Node 12: 9808 470784 org.springframework.core.ResolvableType 13: 12865 411680 java.util.ArrayList$Itr 14: 11799 377568 java.util.concurrent.ConcurrentHashMap$Node 15: 9108 364320 java.util.LinkedHashMap$Entry 16: 7767 310680 java.util.HashMap$KeyIterator 17: 11649 279576 java.lang.StringBuilder 18: 3441 271808 [S 19: 4577 256312 java.util.LinkedHashMap 20: 7391 236512 java.lang.ref.WeakReference 21: 3863 223792 [Ljava.lang.reflect.Method; 22: 2952 212544 java.lang.reflect.Field 23: 5122 195728 [Ljava.lang.String; 24: 7907 189768 java.util.ArrayList 25: 1868 189736 [Z 26: 7011 168264 java.util.Collections$UnmodifiableCollection$1 27: 144 156784 [Ljava.util.concurrent.ConcurrentHashMap$Node; 28: 3869 154760 java.lang.ref.SoftReference
- num：序号
- instances：实例数量
- bytes：占用空间大小
- class name：类名称，[C is a char[]，[S is a short[]，[I is a int[]，[B is a byte[]，[[I is a int[][]
查看总大小排名前30的对象，3是按第三列排序
jmap -histo 92406 | sort -n -r -k 3 | head -30
查看与某某相关的对象
jmap -histo 92406 |grep xxx
导出内存影像：jmap ‐dump:format=b,file=fileName pid
C:\Users\41732>jmap -dump:format=b,file=eureka.hprof 9780 Dumping heap to C:\Users\41732\eureka.hprof ... Heap dump file created C:\Users\41732>
Jinfo
查看jvm参数
C:\Users\41732>jinfo -flags 9780 Attaching to process ID 9780, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.152-b16 Non-default VM flags: -XX:-BytecodeVerificationLocal -XX:-BytecodeVerificationRemote -XX:CICompilerCount=3 -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=4267704320 -XX:MaxNewSize=1422393344 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=891289 60 -XX:OldSize=179306496 -XX:TieredStopAtLevel=1 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC Command line: -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:50964,suspend=y,server=n -XX:TieredStopAtLevel=1 -Xverify:none -Dspring.output.ansi.enabled=always -javaagent:C:\Users\41732\AppData\Local\JetBrains\IntelliJIdea2020.3\c aptureAgent\debugger-agent.jar -Dfile.encoding=UTF-8 C:\Users\41732>
Jstack
分析cpu飙高的原因
1. 找出cpu高的线程
top -p pid -H # -H表示只打印一次
2. 导出线程线程的栈信息
C:\Users\41732>jstack 9780 > aa.text
3. 在导出的栈信息中分析该线程正在执行的状态
注意：top -p 输出的线程号是10进制，而jstack导出的文件线程号是16进制，需要转换。
jstack 19332 | grep -10 4b8f
"http-nio-8080-ClientPoller-0" #20 daemon prio=5 os_prio=0 tid=0x000000001f6a8000 nid=0x1fb8 runnable [0x0000000020cee000] java.lang.Thread.State: RUNNABLE at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method) at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296) at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278) at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159) at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86) - locked <0x000000076d2a11e0> (a sun.nio.ch.Util$3) - locked <0x000000076d2a11d0> (a java.util.Collections$UnmodifiableSet) - locked <0x000000076d2a1080> (a sun.nio.ch.WindowsSelectorImpl) at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97) at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:1052) at java.lang.Thread.run(Thread.java:748) "NioBlockingSelector.BlockPoller-1" #19 daemon prio=5 os_prio=0 tid=0x000000001f680000 nid=0x3c8 runnable [0x0000000020bef000] java.lang.Thread.State: RUNNABLE at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method) at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296) at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278) at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159) at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86) - locked <0x000000076d061bc8> (a sun.nio.ch.Util$3) - locked <0x000000076d060b20> (a java.util.Collections$UnmodifiableSet) - locked <0x000000076d05cdd0> (a sun.nio.ch.WindowsSelectorImpl) at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97) at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:342)
Cpu飙升的原因
- 线程死锁
- 线程内部有死循环
- 程序重有高频率的计算
- IO读写太高
- 频繁的发生GC
- 并发运行中的线程数太多
Jstat
打印GC信息
C:\Users\41732>jstat -gc 9780 1000 10 S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 14336.0 14336.0 4490.6 0.0 64000.0 35918.3 107520.0 12771.6 24448.0 23677.6 3200.0 2998.1 6 0.039 1 0.033 0.073 C:\Users\41732>
