2019独角兽企业重金招聘Python工程师标准>>>
-dump
dump堆到文件,format指定输出格式,live指明是活着的对象,file指定文件名
[root@localhost ~]# jmap -dump:live,format=b,file=dump.hprof 187784
Dumping heap to /home/yxgly/dump.hprof ...
Heap dump file created
-heap
打印heap空间的概要
[root@localhost jdk1.8.0_111]# /usr/local/jdk1.8.0_111/bin/jmap -heap 187784
Attaching to process ID 187784, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14using thread-local object allocation.
Parallel GC with 18 thread(s)Heap Configuration:MinHeapFreeRatio = 0MaxHeapFreeRatio = 100MaxHeapSize = 6442450944 (6144.0MB)NewSize = 1789394944 (1706.5MB)MaxNewSize = 2147483648 (2048.0MB)OldSize = 3579314176 (3413.5MB)NewRatio = 2SurvivorRatio = 8MetaspaceSize = 21807104 (20.796875MB)CompressedClassSpaceSize = 1073741824 (1024.0MB)MaxMetaspaceSize = 17592186044415 MBG1HeapRegionSize = 0 (0.0MB)Heap Usage:
PS Young Generation
Eden Space:capacity = 1683488768 (1605.5MB)used = 1241471032 (1183.9590377807617MB)free = 442017736 (421.5409622192383MB)73.74394505018759% used
From Space:capacity = 54001664 (51.5MB)used = 37876168 (36.12152862548828MB)free = 16125496 (15.378471374511719MB)70.1388905349287% used
To Space:capacity = 54525952 (52.0MB)used = 0 (0.0MB)free = 54525952 (52.0MB)0.0% used
PS Old Generationcapacity = 3926917120 (3745.0MB)used = 312241416 (297.77661895751953MB)free = 3614675704 (3447.2233810424805MB)7.951311587650721% used79807 interned Strings occupying 9359152 bytes.
注意:系统中有多个JDK安装,指定具体的jmap
-histo
打印堆的对象统计,包括对象数、内存大小等
jmap -histo [pid] | head -20 查看top20的实例个数以及内存占用情况
[root@TA30-53 ~]# jmap -histo 31650|head -20num #instances #bytes class name
----------------------------------------------1: 696339 171926288 [B2: 827413 115263552 [C3: 12426 47603720 [I4: 824749 19793976 java.lang.String5: 74743 6577384 org.apache.naming.resources.FileDirContext$FileResourceAttributes6: 192165 6149280 java.util.HashMap$Node7: 103517 4140680 java.util.LinkedHashMap$Entry8: 43700 3622920 [Ljava.lang.Object;9: 33699 2965512 java.lang.reflect.Method10: 23343 2865520 [Ljava.util.HashMap$Node;11: 79293 2537376 java.io.File12: 74768 1794432 java.io.ExpiringCache$Entry13: 15295 1708440 java.lang.Class14: 25572 1227456 java.util.HashMap15: 40743 977832 java.util.ArrayList16: 29255 936160 java.util.concurrent.ConcurrentHashMap$Node17: 6157 763776 [Ljava.lang.String;