1、查看进程号
ps -ef | grep tomcat
2、查看当前内存分配，200ms打印一次
jstat -gc 进程号 200 1
jstat -gc 34480 200 1
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT 14848.0 15360.0 10907.4 0.0 2699776.0 927300.9 1175040.0 636762.8 276908.0 238024.6 31148.0 26766.2 3510 72.635 6 2.610 75.245
S0C：之一个幸存区的大小 S1C：第二个幸存区的大小 S0U：之一个幸存区的使用大小 S1U：第二个幸存区的使用大小 EC：伊甸园区的大小 EU：伊甸园区的使用大小 OC：老年代大小 OU：老年代使用大小 MC： *** 区大小 MU： *** 区使用大小 CCSC:压缩类空间大小 CCSU:压缩类空间使用大小 YGC：年轻代垃圾回收次数 YGCT：年轻代垃圾回收消耗时间 FGC：老年代垃圾回收次数 FGCT：老年代垃圾回收消耗时间 GCT：垃圾回收消耗总时间
3、查看当前堆使用情况
jmap -Heap 34480
Attaching to process ID 34480, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.192-b12 using thread-local object allocation. Parallel GC with 8 thread(s) Heap Configuration: MinHeapFreeRatio = 0 MaxHeapFreeRatio = 100 MaxHeapSize = 8388608000 (8000.0MB) NewSize = 174587904 (166.5MB) MaxNewSize = 2796027904 (2666.5MB) OldSize = 349700096 (333.5MB) NewRatio = 2 SurvivorRatio = 8 MetaspaceSize = 21807104 (20.796875MB) CompressedClassSpaceSize = 1073741824 (1024.0MB) MaxMetaspaceSize = 17592186044415 MB G1HeapRegionSize = 0 (0.0MB) Heap Usage: PS Young Generation Eden Space: capacity = 2764570624 (2636.5MB) used = 1962159688 (1871.2612991333008MB) free = 802410936 (765.2387008666992MB) 70.97520573234594% used From Space: capacity = 15204352 (14.5MB) used = 11169176 (10.651756286621094MB) free = 4035176 (3.8482437133789062MB) 73.46038818359375% used To Space: capacity = 15728640 (15.0MB) used = 0 (0.0MB) free = 15728640 (15.0MB) 0.0% used PS Old Generation capacity = 1203240960 (1147.5MB) used = 652045072 (621.8386383056641MB) free = 551195888 (525.6613616943359MB) 54.19073100702955% used 88789 interned Strings occupying 9011304 bytes.
从23行heap usage 就可以看到当前堆的状况
