JVM统计监测工具jstat常用命令使用技巧

jstat(JVM统计监测工具)

语法格式如下：

jstat [ generalOption | outputOptions vmid [interval[s|ms] [count]] ] vmid是虚拟机ID，在Linux/Unix系统上一般就是进程ID。interval是采样时间间隔。count是采样数目。比如下面输出的是GC信息，采样时间间隔为250ms，采样数为4：

root@ubuntu:/# jstat -gc 21711 250 4S0C S1C S0U S1U EC EU OC OU PC PU YGC YGCT FGC FGCT GCT192.0 192.0 64.0 0.0 6144.0 1854.9 32000.0 4111.6 55296.0 25472.7 702 0.431 3 0.218 0.649192.0 192.0 64.0 0.0 6144.0 1972.2 32000.0 4111.6 55296.0 25472.7 702 0.431 3 0.218 0.649192.0 192.0 64.0 0.0 6144.0 1972.2 32000.0 4111.6 55296.0 25472.7 702 0.431 3 0.218 0.649192.0 192.0 64.0 0.0 6144.0 2109.7 32000.0 4111.6 55296.0 25472.7 702 0.431 3 0.218 0.649 要明白上面各列的意义，先看JVM堆内存布局：

可以看出：

堆内存 = 年轻代 + 年老代 + 永久代年轻代 = Eden区 + 两个Survivor区(From和To) 现在来解释各列含义：

S0C、S1C、S0U、S1U：Survivor 0/1区容量(Capacity)和使用量(Used)EC、EU：Eden区容量和使用量OC、OU：年老代容量和使用量PC、PU：永久代容量和使用量YGC、YGT：年轻代GC次数和GC耗时FGC、FGCT：Full GC次数和Full GC耗时GCT：GC总耗时

jdk8各参数含义(参考官网)：jstat -gcS0C: 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 old space capacity (kB).

OU: Old space utilization (kB).

MC: Metaspace capacity (kB).(元空间容量)

MU: Metacspace utilization (kB).

CCSC: Compressed class space capacity (kB).

CCSU: Compressed class space used (kB).

YGC: Number of young generation garbage collection events.

YGCT: Young generation garbage collection time.

FGC: Number of full GC events.

FGCT: Full garbage collection time.

GCT: Total garbage collection time.

jstat -gcutil显示的是各区占用的百分比如下：S0: Survivor space 0 utilization as a percentage of the space's current capacity.

S1: Survivor space 1 utilization as a percentage of the space's current capacity.

E: Eden space utilization as a percentage of the space's current capacity.

O: Old space utilization as a percentage of the space's current capacity.

M: Metaspace utilization as a percentage of the space's current capacity.

CCS: Compressed class space utilization as a percentage.

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.