jstat - Tool for JVM Statistics Monitoring

In this article we are going to elaborate the jstat command tool which is a part of JAVA commands (comes with jdk package). This article is the continuation of this previous article.

As we know the standard format of commands in java, the jstat command also have the format(in command prompt)
jstat [ generalOption | outputOptions vmid [interval[s|ms] [count]] ]

In here,
generalOption : Options commons for all commands, I will define in bottom.
outputOptions : Output specific options consisting a single stateOption and any of -t/-h/-J
vmid : Virtual machine identifier, a string indicating the target JVM. I will explain in bottom.
interval[s|ms] : Interval time seconds (s) / milliseconds (ms). jstat will produce its output at each interval.
count : Number of samples to display.

jstat shows performance statistics for an  JVM(Instrumented HotSpot). jstat use a identifier to get the JVM info.

jstat Options : 
General Options :
-help : Shows help message. (same as other commands)
-version : Shows version information.(same as other commands)
-options : Shows list of statistics options

Output Options :  Determines the content and the format of jstat's output. It has two part, stateOption and any of -t/-h/-J.
-Output formatted as table (columns are in space)

-t n : Shows time stamp(in second) as 1st column.
-h n : Sets the frequency of displaying header. 
-J[option] : Pass java option to the java app launcher.

-stateOption: Defines the statistics info of jstat . It has following options 
class : Statistics on the class loader. Details of shown columns are
Loaded : Number of loaded classes
Bytes : Number loaded memory in Kb.
Unloaded : Number of classes unloaded.
Bytes : Number of Kbytes unloaded.
Time : Time spent for class load and unload operations.

compiler : Statistics of the HotSpot Just-in-Time compiler. Columns details are

Compiled : Number of compilation tasks.
Failed : Number of compilation failed tasks.
Invalid : Number of compilation invalidated tasks.
Time : Time for compilation .
FailedType : Last failed Compile type.
FailedMethod : Last compile failed Class name and method.

gc : Statistics of garbage collected(GC) heap.Columns details are
S0C : Current survivor space 0 (KB).
S1C : Current survivor space 1 (KB).
S0U : Survivor space 0 (KB).
S1U : Survivor space 1 (KB).
EC : Current Eden space (KB).
EU : Eden space utilization (KB).
OC : Current old space (KB).
OU : Old space (KB).
PC : Current permanent space (KB).
PU : Permanent space (KB).
YGC : Number of young generation GC Events.
YGCT : Young generation GC Time.
FGC : Number of full GC events.
FGCT : Full garbage collection time.
GCT : Total garbage collection time.

gccapacity : Statistics of generations and their corresponding spaces.Columns details are
NGCMN : Min New generation capacity (KB).
NGCMX : Max New generation capacity (KB).
NGC : Current new generation capacity (KB).
S0C : Current survivor space 0 capacity (KB).
S1C : Current survivor space 1 capacity (KB).
EC :  Current eden space capacity (KB).
OGCMN : Minimum old generation capacity (KB).
OGCMX : Maximum old generation capacity (KB).
OGC : Current old generation capacity (KB).
OC : Current old space capacity (KB).
PGCMN : Minimum permanent generation capacity (KB).
PGCMX : Maximum Permanent generation capacity (KB).
PGC : Current Permanent generation capacity (KB).
PC : Current Permanent space capacity (KB).
YGC : Number of Young generation GC Events.
FGC : Number of Full GC Events.

gccause : Summary of garbage collection statistics (same to -gcutil but including last and current GC events). Additional columns other than gcutil are
LGCC :Cause of last Garbage Collection.
GCC : Cause of current Garbage Collection.

gcnew :Statistics of the behavior of new generation(in memory heap). Columns details are
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).
TT : Tenuring threshold.
MTT : Maximum tenuring threshold.
DSS : Desired survivor size (KB).
EC : Current eden space capacity (KB).
EU : Eden space utilization (KB).
YGC : Number of young generation GC events.
YGCT : Young generation garbage collection time.

gcnewcapacity : Statistics of the sizes of the new generations and its corresponding spaces. Columns details are
NGCMN :Minimum New Generation Capacity (KB).
NGCMX : Maximum New Generation Capacity (KB).
NGC : Current New Generation Capacity (KB).
S0CMX : Maximum survivor space 0 capacity (KB).
S0C : Current survivor space 0 capacity (KB).
S1CMX : Maximum survivor space 1 capacity (KB).
S1C : Current survivor space 1 capacity (KB).
ECMX : Maximum eden space capacity (KB).
EC : Current eden space capacity (KB).
YGC : Number of young generation GC events.
FGC : Number of Full GC Events.

gcold : Statistics of the behavior of the old and permanent generations(in memory heap). Columns details are
PC : Current permanent space capacity (KB).
PU : Permanent space utilization (KB).
OC : Current old space capacity (KB).
OU : Old space utilization (KB).
YGC : Number of young generation GC events.
FGC : Number of full GC events.
FGCT : Full garbage collection time.
GCT : Total garbage collection time.

gcoldcapacity : Statistics of the sizes of the old generation. Columns details are
OGCMN : Minimum Old generation capacity (KB).
OGCMX : Maximum Old generation capacity (KB).
OGC : Current old generation capacity (KB).
OC : Current old space capacity (KB).
YGC : Number of young generation GC events.
FGC : Number of full GC events.
FGCT : Full garbage collection time.
GCT : Total garbage collection time.

gcpermcapacity : Statistics of the sizes of the Permanent Generation. Columns details are
PGCMN : Minimum permanent generation capacity (KB).
PGCMX : Maximum permanent generation capacity (KB).
PGC : Current permanent generation capacity (KB).
PC : Current permanent space capacity (KB).
YGC : Number of young generation GC events.
FGC : Number of full GC events.
FGCT : Full garbage collection time.
GCT : Total garbage collection time.

gcutil : Summary of garbage collection(GC) statistics. Columns details are
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.
P : Permanent space utilization as a percentage of the space's current capacity.
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.

printcompilation : HotSpot compilation method statistics. Columns details are
Compiled : Number of compiled tasks .
Size : Number of bytes of bytecode for the method.
Type : Compilation type.
Method : Class name and method name identifying the compiled method.

So, now VMI, the virtual machine Identifier, in shortcut vmid. It's a simple way to specify a vm. The syntax of a vmid string is
[protocol:][//]lvmid[@hostname][:port][/servername]
protocol : Communication protocol.
lvmid : The local virtual machine identifier for the target JVM.(kind of pid of a OS)
hostname :A hostname or IP address.
port :The default port for communicating with the remote server. For the default rmi protocol, the port indicates the port number for the rmiregistry on the remote host.
servername : It depends on implementation. Like as ,
For the optimized local protocol, this field is ignored.
For the rmi protocol, it represents the name of the RMI remote object on the remote host.

Example :


I ran jconsole application to get its PID and monitor jconsole is self for statistics. I use this command where my PID(of jconsole)= 7972, interval time 250ms and 7 time recording. 
jstat -gcutil 7972 250 7

Thanks...:) 

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