In this article we are going to see the jstat commands.

What is jstat?

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

Syntax

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 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. The format for these two fields is consistent with the HotSpot -XX:+PrintCompilation option.

What is VMID

The virtual machine Identifier, in shortcut vmid. It’s a simple way to identify a vm.

syntax

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

Where :

  • 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 ,

Example :

I have run jconsole application to get its PID and monitor jconsole itself for statistics. I have used this command where my PID(of jconsole)= 7972, interval time 250ms and 7 times recording.

jstat -gcutil 7972 250 7

jstat

Notes :

  • 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.

Thanks…:)