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Mastering jstat: How to Monitor JVM Performance with Command-Line Options

This guide explains how to use the jstat command-line tool to monitor Java Virtual Machine performance metrics such as garbage collection, memory usage, and compilation time, detailing its syntax, options, intervals, counts, and providing concrete examples with expected outputs.

Programmer DD

Nov 12, 2020

Mastering jstat: How to Monitor JVM Performance with Command-Line Options

Purpose

jstat is a tool for retrieving performance statistics of a running Java Virtual Machine (JVM), including garbage collection activity, memory sizes, and compilation times.

Command Syntax

jstat [ generalOption | outputOptions vmid [interval[s|ms] [count]] ]

generalOption

jstat -help|-options

Running jstat -options displays the available options (see the option list below).

-class : class‑loading statistics

-compiler : JIT compilation statistics

-gc : heap statistics

-gcutil : same as -gc but shows used space as a percentage of total

-gccapacity : maximum and minimum space of each heap region

-gccause : garbage‑collection cause information

-gcnew : young‑generation statistics

-gcnewcapacity : capacity information for the young generation

-gcold : old‑generation statistics

-gcoldcapacity : capacity information for the old generation

-printcompilation : details of methods compiled by the JIT

outputOptions

One or more output options, which may include a single stat option together with any -t, -h and -J flags.

vmid

The identifier of the target JVM (process ID). ps -ef | grep java or

jps -l

interval

Sampling interval in the specified unit, seconds ( s) or milliseconds ( ms). The default unit is milliseconds. It must be a positive integer; if provided, jstat emits output at each interval.

count

Number of output samples. The default is infinite, meaning jstat continues until the JVM exits or the command is stopped. It must be a positive integer.

Examples

-class option

Input

jstat -class 29271 1000 20

Output

Loaded  Bytes  Unloaded  Bytes     Time
 22182 42401.0      638   847.4      39.52
 22182 42401.0      638   847.4      39.52

loaded : amount of data loaded

bytes : number of bytes loaded

unloaded : number of classes unloaded

bytes : bytes of unloaded classes

time : time spent loading and unloading

-compiler option

Input

jstat -compiler 29271 1000 20

Output

Compiled  Failed  Invalid   Time   FailedType  FailedMethod
    6663      3       0   108.64          1  org/apache/jasper/xmlparser/ParserUtils convert
    6663      3       0   108.64          1  org/apache/jasper/xmlparser/ParserUtils convert

Compiled : number of compilation tasks executed

Failed : number of compilation tasks that failed

Invalid : number of invalid compilations

Time : time spent compiling

FailedType : type of failed task

FailedMethod : method that failed to compile

-gc option

Input

jstat -gc 29271 1000 20

Output

S0C    S1C    S0U    S1U      EC       EU        OC          OU       PC      PU    YGC   YGCT    FGC    FGCT     GCT
4096.0 4096.0  0.0   3088.4 691200.0 85378.5  1398272.0   337712.4  262144.0 121554.1  25374  413.439   7      5.536   418.975
4096.0 4096.0  0.0   3088.4 691200.0 85727.0  1398272.0   337712.4  262144.0 121554.1  25374  413.439   7      5.536   418.975

S0C : capacity of the first survivor space

S1C : capacity of the second survivor space

S0U : usage of the first survivor space

S1U : usage of the second survivor space

EC : total capacity of the Eden space

EU : used capacity of the Eden space

OC : total capacity of the old generation

OU : used capacity of the old generation

PC : capacity of the permanent generation (KB)

PU : used capacity of the permanent generation (KB)

YGC : number of young‑generation garbage collections

YGCT : time spent in young‑generation GC

FGC : number of full (old‑generation) garbage collections

FGCT : time spent in full GC

GCT : total garbage‑collection time

-gcutil option

Input

jstat -gcutil 29271 1000 20

Output

S0      S1      E      O      P   YGC   YGCT    FGC    FGCT     GCT
  83.70   0.00  62.04  24.11  46.37  25373  413.423     7    5.536  418.958
  83.70   0.00  62.06  24.11  46.37  25373  413.423     7    5.536  418.958

S0 : capacity of the first survivor space

S1 : capacity of the second survivor space

E : total capacity of the Eden space

O : total capacity of the old generation

P : capacity of the permanent generation (KB)

YGC : young‑generation GC count

YGCT : young‑generation GC time

FGC : full GC count

FGCT : full GC time

GCT : total GC time

-gccapacity option

Input

jstat -gccapacity 29271 1000 20

Output

NGCMN    NGCMX      NGC      S0C   S1C       EC      OGCMN      OGCMX       OGC          OC      PGCMN    PGCMX      PGC       PC     YGC    FGC
699392.0 699392.0 699392.0 4096.0 4096.0 691200.0  1398272.0  1398272.0  1398272.0  1398272.0 262144.0 262144.0 262144.0 262144.0  25374     7
699392.0 699392.0 699392.0 4096.0 4096.0 691200.0  1398272.0  1398272.0  1398272.0  1398272.0 262144.0 262144.0 262144.0 262144.0  25374     7

NGCMN : initial capacity of the young generation (KB)

NGCMX : maximum capacity of the young generation (KB)

NGC : current capacity of the young generation

S0C : current capacity of survivor space 0 (KB)

S1C : current capacity of survivor space 1 (KB)

EC : capacity of the Eden space

OGCMN : initial capacity of the old generation (KB)

OGCMX : maximum capacity of the old generation (KB)

OGC : current capacity of the old generation

OC : capacity of the old generation

PGCMN : initial size of the permanent generation (KB)

PGCMX : maximum size of the permanent generation (KB)

PGC : current size of the permanent generation

PC : capacity of the permanent generation

YGC : young‑generation GC count

FGC : full GC count

-gccause option

Input

jstat -gccause 29271 1000 20

Output

S0      S1      E      O      P   YGC   YGCT    FGC    FGCT     GCT    LGCC                 GCC
  0.00   75.40  72.95  24.15  46.37  25374  413.439     7    5.536  418.975 Allocation Failure   No GC
  0.00   75.40  73.03  24.15  46.37  25374  413.439     7    5.536  418.975 Allocation Failure   No GC

S0 : capacity of the first survivor space

S1 : capacity of the second survivor space

E : total capacity of the Eden space

O : total capacity of the old generation

P : capacity of the permanent generation (KB)

YGC : young‑generation GC count

YGCT : young‑generation GC time

FGC : full GC count

FGCT : full GC time

GCT : total GC time

LGCC : most recent GC cause

GCC : current GC cause

-gcnew option

Input

jstat -gcnew 29271 1000 20

Output

S0C    S1C    S0U    S1U   TT MTT  DSS      EC       EU      YGC    YGCT
4096.0 4096.0    0.0 3088.4  1  15 4096.0 691200.0 588124.7  25374  413.439
4096.0 4096.0    0.0 3088.4  1  15 4096.0 691200.0 588759.6  25374  413.439

S0C : capacity of the first survivor space

S1C : capacity of the second survivor space

S0U : usage of the first survivor space

S1U : usage of the second survivor space

TT : maximum tenuring threshold

MTT : current tenuring threshold

DSS : desired survivor size

EC : total capacity of the Eden space

EU : used capacity of the Eden space

YGC : young‑generation GC count

YGCT : young‑generation GC time

-gcnewcapacity option

Input

jstat -gcnewcapacity 29271 1000 20

Output

NGCMN      NGCMX       NGC      S0CMX    S0C    S1CMX    S1C       ECMX        EC      YGC   FGC
  699392.0   699392.0   699392.0 232960.0 4096.0 232960.0 4096.0   698368.0   691200.0 25374   7
  699392.0   699392.0   699392.0 232960.0 4096.0 232960.0 4096.0   698368.0   691200.0 25374   7

NGCMN : initial capacity of the young generation (KB)

NGCMX : maximum capacity of the young generation (KB)

NGC : current capacity of the young generation

S0CMX : maximum capacity of survivor space 0 (KB)

S0C : current capacity of survivor space 0 (KB)

S1CMX : maximum capacity of survivor space 1 (KB)

S1C : current capacity of survivor space 1 (KB)

ECMX : maximum capacity of the Eden space

EC : current capacity of the Eden space

YGC : young‑generation GC count

FGC : full GC count

-gcold option

Input

jstat -gcold 29271 1000 20

Output

PC       PU        OC          OU       YGC    FGC    FGCT     GCT
262144.0 121554.1   1398272.0    337896.5  25375     7    5.536  418.995
262144.0 121554.1   1398272.0    337896.5  25375     7    5.536  418.995

PC : permanent generation capacity

PU : permanent generation used

OC : old generation capacity

OU : old generation used

YGC : young‑generation GC count

FGC : full GC count

FGCT : full GC time

GCT : total GC time

-gcoldcapacity option

Input

jstat -gcoldcapacity 29271 1000 20

Output

OGCMN       OGCMX        OGC          OC       YGC   FGC    FGCT      GCT
  1398272.0   1398272.0   1398272.0   1398272.0 25373   7    5.536   418.958
  1398272.0   1398272.0   1398272.0   1398272.0 25373   7    5.536   418.958

OGCMN : initial capacity of the old generation (KB)

OGCMX : maximum capacity of the old generation (KB)

OGC : current capacity of the old generation

OC : old generation capacity

YGC : young‑generation GC count

FGC : full GC count

FGCT : full GC time

GCT : total GC time

-printcompilation option

Input

jstat -printcompilation 29271 1000 20

Output

Compiled  Size  Type Method
    6663   3093    1 com/alibaba/dubbo/registry/support/FailbackRegistry retry
    6663   3093    1 com/alibaba/dubbo/registry/support/FailbackRegistry retry

Compiled : number of compilation tasks

Size : bytecode size of the compiled method

Type : compilation type

Method : method that was compiled

Reference Documentation

https://docs.oracle.com/javase/7/docs/technotes/tools/share/jstat.html#general_options

Original Source

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Java performance JVM Monitoring command-line jstat GC statistics

Written by

Programmer DD

A tinkering programmer and author of "Spring Cloud Microservices in Action"

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