jstat用法

jstat（JVM Statistics Monitoring Tool）是用于监视虚拟机各种运行状态信息的命令行工具。它可以显示本地或者远程虚拟机进程中的类装载、内存、垃圾收集、JIT编译等运行数据，在没有GUI图形界面，只提供了纯文本控制台环境的服务器上，它将是运行期定位虚拟机性能问题的首选工具。

jstat命令格式为：

jstat [ option vmid [interval[s|ms] [count]] ]

对于命令格式中的VMID与LVMID需要特别说明一下：如果是本地虚拟机进程，VMID与LVMID是一致的，如果是远程虚拟机进程，那VMID的格式应当是：

[protocol:][//]lvmid[@hostname[:port]/servername]

参数interval和count代表查询间隔和次数，如果省略这两个参数，说明只查询一次。假设需要每250毫秒查询一次进程2764垃圾收集状况，一共查询20次，那命令应当是：

jstat -gc 2764 250 20

选项option代表着用户希望查询的虚拟机信息，主要分为3类：类装载、垃圾收集、运行期编译状况，其参数如下：

Option	Displays...
class	Statistics on the behavior of the class loader
compiler	Statistics on the behavior of the HotSpot Just-In-Time compiler
gc	Statistics on the behavior of the garbage collected heap
gccapacity	Statistics of the capacities of the generations and their corresponding spaces.
gccause	Summary of garbage collection statistics (same as -gcutil), with the cause of the last and current (if applicable) garbage collection events.
gcnew	Statistics of the behavior of the new generation.
gcnewcapacity	Statistics of the sizes of the new generations and its corresponding spaces.
gcold	Statistics of the behavior of the old and permanent generations.
gcoldcapacity	Statistics of the sizes of the old generation.
gcpermcapacity	Statistics of the sizes of the permanent generation.
gcutil	Summary of garbage collection statistics.
printcompilation	Summary of garbage collection statistics.

jstat执行样例：

IvydeMacBook-Air% jstat -gc 536
 S0C    S1C    S0U    S1U      EC       EU        OC         OU       PC     PU    YGC     YGCT    FGC    FGCT     GCT
2560.0 2560.0  0.0    0.0   16896.0   5070.7   43520.0      0.0     21504.0 2901.1      0    0.000   0      0.000    0.000

显示	说明
S0C	Current survivor space 0 capacity(KB).
S1C	Current survivor space 1 capacity(KB).
S0U	Survivor space 0 utilization(KB).
S1U	Survivor space 1 utilization(KB).
EC	Current eden space capacity(KB).
EU	Eden space utilization(KB).
OC	Current oldpace capacity(KB).
OU	Old space utilization(KB).
PC	Current permanet space capacity(KB).
PU	Permanent space utilization(KB).
YGC	Number of young generation GC Events.
YGCT	Young generation garbage collection time.
FGC	Number of full GC events
FGCT	Full garbage collection time.
GCT	Total garbage collection time.