解决JMap抓取heap使用统计信息报错的问题

如下所示：

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/jmap jdk small version diffrent from jvm jdk vesionbegin///
[dev@iZ2ze8us9p89pfk02m9vs1Z ~]$ jmap -heap 1541
Attaching to process ID 1541, please wait...
Error attaching to process: sun.jvm.hotspot.debugger.DebuggerException: cannot open binary file
sun.jvm.hotspot.debugger.DebuggerException: sun.jvm.hotspot.debugger.DebuggerException: cannot open binary file
at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal$LinuxDebuggerLocalWorkerThread.execute(LinuxDebuggerLocal.java:163)
at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal.attach(LinuxDebuggerLocal.java:278)
at sun.jvm.hotspot.HotSpotAgent.attachDebugger(HotSpotAgent.java:671)
at sun.jvm.hotspot.HotSpotAgent.setupDebuggerLinux(HotSpotAgent.java:611)
at sun.jvm.hotspot.HotSpotAgent.setupDebugger(HotSpotAgent.java:337)
at sun.jvm.hotspot.HotSpotAgent.go(HotSpotAgent.java:304)
at sun.jvm.hotspot.HotSpotAgent.attach(HotSpotAgent.java:140)
at sun.jvm.hotspot.tools.Tool.start(Tool.java:185)
at sun.jvm.hotspot.tools.Tool.execute(Tool.java:118)
at sun.jvm.hotspot.tools.HeapSummary.main(HeapSummary.java:49)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.tools.jmap.JMap.runTool(JMap.java:201)
at sun.tools.jmap.JMap.main(JMap.java:130)
Caused by: sun.jvm.hotspot.debugger.DebuggerException: cannot open binary file
at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal.attach0(Native Method)
at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal.access$100(LinuxDebuggerLocal.java:62)
at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal$1AttachTask.doit(LinuxDebuggerLocal.java:269)
at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal$LinuxDebuggerLocalWorkerThread.run(LinuxDebuggerLocal.java:138)
/jmap jdk small version diffrent from jvm jdk vesionend///

/jmap jdk big version diffrent from jvm jdk vesionbegin///
Attaching to process ID 30413, please wait...
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.tools.jmap.JMap.runTool(JMap.java:201)
at sun.tools.jmap.JMap.main(JMap.java:130)
Caused by: java.lang.InternalError: void* type hasn't been seen when parsing int*
at sun.jvm.hotspot.HotSpotTypeDataBase.recursiveCreateBasicPointerType(HotSpotTypeDataBase.java:721)
at sun.jvm.hotspot.HotSpotTypeDataBase.lookupType(HotSpotTypeDataBase.java:134)
at sun.jvm.hotspot.HotSpotTypeDataBase.lookupOrCreateClass(HotSpotTypeDataBase.java:631)
at sun.jvm.hotspot.HotSpotTypeDataBase.createType(HotSpotTypeDataBase.java:751)
at sun.jvm.hotspot.HotSpotTypeDataBase.readVMTypes(HotSpotTypeDataBase.java:195)
at sun.jvm.hotspot.HotSpotTypeDataBase.<init>(HotSpotTypeDataBase.java:89)
at sun.jvm.hotspot.HotSpotAgent.setupVM(HotSpotAgent.java:395)
at sun.jvm.hotspot.HotSpotAgent.go(HotSpotAgent.java:305)
at sun.jvm.hotspot.HotSpotAgent.attach(HotSpotAgent.java:140)
at sun.jvm.hotspot.tools.Tool.start(Tool.java:185)
at sun.jvm.hotspot.tools.Tool.execute(Tool.java:118)
at sun.jvm.hotspot.tools.HeapSummary.main(HeapSummary.java:49)
... 6 more
/jmap jdk big version diffrent from jvm jdk vesionend///
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【问题】

执行jmap -heap命令是报错，方法返回参数类型不匹配

【分析】

考虑执行jmap的jdk版本同目标jvm的jdk版本不一致：

1> 如果jmap的jdk版本比目标jvm高，执行会提示方法不兼容错误

2> 如果jmap的jdk版本比目标jvm低，执行会提示jdk版本不一致错误

【解决】

采用执行jmap的jdk版本同目标jvm的jdk版本保持一致。

补充知识：jmap -heap返回结果分析

using parallel threads in the new generation.
using thread-local object allocation.
Concurrent Mark-Sweep GC
Heap Configuration:
 MinHeapFreeRatio   = 40
 MaxHeapFreeRatio   = 70
 MaxHeapSize    = 4294967296 (4096.0MB)
 NewSize     = 858980352 (819.1875MB)
 MaxNewSize    = 858980352 (819.1875MB)
 OldSize     = 3435986944 (3276.8125MB)
 NewRatio     = 4
 SurvivorRatio   = 8
 MetaspaceSize   = 21807104 (20.796875MB)
 CompressedClassSpaceSize = 1073741824 (1024.0MB)
 MaxMetaspaceSize   = 17592186044415 MB
 G1HeapRegionSize   = 0 (0.0MB)

Heap Usage:

新生代

New Generation (Eden + 1 Survivor Space):
 capacity = 773128192 (737.3125MB)
 used  = 95478696 (91.05558013916016MB)
 free  = 677649496 (646.2569198608398MB)
 12.349659084738175% used
Eden Space:
 capacity = 687276032 (655.4375MB)
 used  = 95478696 (91.05558013916016MB)
 free  = 591797336 (564.3819198608398MB)
 13.892336056322709% used
From Space:
 capacity = 85852160 (81.875MB)
 used  = 0 (0.0MB)
 free  = 85852160 (81.875MB)
 0.0% used
To Space:
 capacity = 85852160 (81.875MB)
 used  = 0 (0.0MB)
 free  = 85852160 (81.875MB)
 0.0% used
concurrent mark-sweep generation:
 capacity = 3435986944 (3276.8125MB)
 used  = 119572370833685648 (1.1403309901588979E11MB)
 free  = 17478152948676 MB
 3.480000732903997E9% used

根据以上数据，我们来check一些ratio：

NewRatio = 2
Eden Space capacity = 1063256064 (1014.0MB)
From Space capacity = 4718592 (4.5MB)
To Space capacity = 5242880 (5.0MB)

简单加法，

New size=1014.0+4.5+5.0=1023.5MB

MaxHeapSize = 3221225472 (3072.0MB)

年轻代占比：

1023.5/3072.0=1/3。

换算NewRatio的计算，老年代/新生代，结果为2

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