运行日志、异常堆栈、堆使用情况、GC情况、JVM参数情况、线程情况等
给一个系统定位问题的时候,知识、经验是关键,数据是依据,工具是运用知识处理数据的手段。
为了便于我们排查和解决问题,jdk/lib/tools.jar中类库的一层薄包装
jps
显示当前所有java进程pid的命令
jinfo
实时查看和调整虚拟机参数
jstat
显示进程中的类装载、内存、垃圾收集、JIT编译等运行数据
jstat -gc 3331 250 20
:查询进程2764的垃圾收集情况,每250毫秒查询一次,一共查询20次。
jstat -calss
:查询类装载、类卸载、总空间以及所消耗的时间
jmap
生成堆转储快照(heapdump)
jmap -heap 3331
:查看java 堆(heap)使用情况
jmap -histo 3331
:查看堆内存(histogram)中的对象数量及大小
jmap -histo:live 3331
:JVM会先触发gc,然后再统计信息
jhat
一般与jmap搭配使用,用来分析jmap生成的堆转储文件
由于有很多可视化工具(Eclipse Memory Analyzer 、IBM HeapAnalyzer)可以替代,所以很少用。不过在没有可视化工具的机器上也是可用的
jmap -dump:format=b,file=heapDump 3331
jstack
jstack 3331
:查看线程情况jstack -F 3331
:正常输出不被响应时,使用该指令jstack -l 3331
:除堆栈外,显示关于锁的附件信息
频繁GC问题或内存溢出问题
一、使用jps
查看线程ID
二、使用jstat -gc 3331 250 20
查看gc情况,一般比较关注PERM区的情况,查看GC的增长情况。
三、使用jstat -gccause
:额外输出上次GC原因
四、使用jmap -dump:format=b,file=heapDump 3331
生成堆转储文件
五、使用jhat或者可视化工具(Eclipse Memory Analyzer 、IBM HeapAnalyzer)分析堆情况。
六、结合代码解决内存溢出或泄露问题。
死锁问题
一、使用jps
查看线程ID
二、使用jstack 3331
:查看线程情况
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