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jstat Monitoring Tools jstat

NAME

jstat – Monitors Java Virtual Machine (JVM) statistics. This command is
experimental and unsupported.

SYNOPSIS

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

generalOption
A single general command-line option -help or -options. See General
Options.

outputOptions
One or more output options that consist of a single statOption,
plus any of the -t, -h, and -J options. See Output Options.

vmid
Virtual machine identifier, which is a string that indicates the
target JVM. The general syntax is the following:

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

The syntax of the vmid string corresponds to the syntax of a URI.
The vmid string can vary from a simple integer that represents a
local JVM to a more complex construction that specifies a
communications protocol, port number, and other
implementation-specific values. See Virtual Machine Identifier.

interval [s|ms] Sampling interval in the specified units, seconds (s) or
milliseconds (ms). Default units are milliseconds. Must be a
positive integer. When specified, the jstat command produces its
output at each interval.

count
Number of samples to display. The default value is infinity which
causes the jstat command to display statistics until the target JVM
terminates or the jstat command is terminated. This value must be a
positive integer.

DESCRIPTION

The jstat command displays performance statistics for an instrumented
Java HotSpot VM. The target JVM is identified by its virtual machine
identifier, or vmid option.

VIRTUAL MACHINE IDENTIFIER
The syntax of the vmid string corresponds to the syntax of a URI:

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

protocol
The communications protocol. If the protocol value is omitted and a
host name is not specified, then the default protocol is a
platform-specific optimized local protocol. If the protocol value
is omitted and a host name is specified, then the default protocol
is rmi.

lvmid
The local virtual machine identifier for the target JVM. The lvmid
is a platform-specific value that uniquely identifies a JVM on a
system. The lvmid is the only required component of a virtual
machine identifier. The lvmid is typically, but not necessarily,
the operating system’s process identifier for the target JVM
process. You can use the jps command to determine the lvmid. Also,
you can determine the lvmid on Solaris, Linux, and OS X platforms
with the ps command, and on Windows with the Windows Task Manager.

hostname
A hostname or IP address that indicates the target host. If the
hostname value is omitted, then the target host is the local host.

port
The default port for communicating with the remote server. If the
hostname value is omitted or the protocol value specifies an
optimized, local protocol, then the port value is ignored.
Otherwise, treatment of the port parameter is
implementation-specific. For the default rmi protocol, the port
value indicates the port number for the rmiregistry on the remote
host. If the port value is omitted and the protocol value indicates
rmi, then the default rmiregistry port (1099) is used.

servername
The treatment of the servername parameter depends on
implementation. 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.

OPTIONS

The jstat command supports two types of options, general options and
output options. General options cause the jstat command to display
simple usage and version information. Output options determine the
content and format of the statistical output.

All options and their functionality are subject to change or removal in
future releases.

General Options
If you specify one of the general options, then you cannot specify any
other option or parameter.

-help
Displays a help message.

-options
Displays a list of static options. See Output Options.

Output Options
If you do not specify a general option, then you can specify output
options. Output options determine the content and format of the jstat
command’s output, and consist of a single statOption, plus any of the
other output options (-h, -t, and -J). The statOption must come first.

Output is formatted as a table, with columns that are separated by
spaces. A header row with titles describes the columns. Use the -h
option to set the frequency at which the header is displayed. Column
header names are consistent among the different options. In general, if
two options provide a column with the same name, then the data source
for the two columns is the same.

Use the -t option to display a time stamp column, labeled Timestamp as
the first column of output. The Timestamp column contains the elapsed
time, in seconds, since the target JVM started. The resolution of the
time stamp is dependent on various factors and is subject to variation
due to delayed thread scheduling on heavily loaded systems.

Use the interval and count parameters to determine how frequently and
how many times, respectively, the jstat command displays its output.

Note: Do not to write scripts to parse the jstat command’s output
because the format might change in future releases. If you write
scripts that parse jstat command output, then expect to modify them for
future releases of this tool.

-statOption
Determines the statistics information the jstat command displays.
The following lists the available options. Use the -options general
option to display the list of options for a particular platform
installation. See Stat Options and Output.

class: Displays statistics about the behavior of the class loader.

compiler: Displays statistics about the behavior of the Java
HotSpot VM Just-in-Time compiler.

gc: Displays statistics about the behavior of the garbage collected
heap.

gccapacity: Displays statistics about the capacities of the
generations and their corresponding spaces.

gccause: Displays a summary about garbage collection statistics
(same as -gcutil), with the cause of the last and current (when
applicable) garbage collection events.

gcnew: Displays statistics of the behavior of the new generation.

gcnewcapacity: Displays statistics about the sizes of the new
generations and its corresponding spaces.

gcold: Displays statistics about the behavior of the old generation
and metaspace statistics.

gcoldcapacity: Displays statistics about the sizes of the old
generation.

gcmetacapacity: Displays statistics about the sizes of the
metaspace.

gcutil: Displays a summary about garbage collection statistics.

printcompilation: Displays Java HotSpot VM compilation method
statistics.

-h n
Displays a column header every n samples (output rows), where n is
a positive integer. Default value is 0, which displays the column
header the first row of data.

-t
Displays a timestamp column as the first column of output. The time
stamp is the time since the start time of the target JVM.

-JjavaOption
Passes javaOption to the Java application launcher. For example,
-J-Xms48m sets the startup memory to 48 MB. For a complete list of
options, see java.

Stat Options and Output
The following information summarizes the columns that the jstat command
outputs for each statOption.

-class option
Class loader statistics.

Loaded: Number of classes loaded.

Bytes: Number of kBs loaded.

Unloaded: Number of classes unloaded.

Bytes: Number of Kbytes unloaded.

Time: Time spent performing class loading and unloading operations.

-compiler option
Java HotSpot VM Just-in-Time compiler statistics.

Compiled: Number of compilation tasks performed.

Failed: Number of compilations tasks failed.

Invalid: Number of compilation tasks that were invalidated.

Time: Time spent performing compilation tasks.

FailedType: Compile type of the last failed compilation.

FailedMethod: Class name and method of the last failed compilation.

-gc option
Garbage-collected heap statistics.

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 old space capacity (kB).

OU: Old space utilization (kB).

MC: Metaspace capacity (kB).

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.

-gccapacity option
Memory pool generation and space capacities.

NGCMN: Minimum new generation capacity (kB).

NGCMX: Maximum 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).

MCMN: Minimum metaspace capacity (kB).

MCMX: Maximum metaspace capacity (kB).

MC: Metaspace capacity (kB).

CCSMN: Compressed class space minimum capacity (kB).

CCSMX: Compressed class space maximum capacity (kB).

CCSC: Compressed class space capacity (kB).

YGC: Number of young generation GC events.

FGC: Number of full GC events.

-gccause option
This option displays the same summary of garbage collection
statistics as the -gcutil option, but includes the causes of the
last garbage collection event and (when applicable) the current
garbage collection event. In addition to the columns listed for
-gcutil, this option adds the following columns.

LGCC: Cause of last garbage collection

GCC: Cause of current garbage collection

-gcnew option
New generation statistics.

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 option
New generation space size statistics.

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 option
Old generation and metaspace behavior statistics.

MC: Metaspace capacity (kB).

MU: Metaspace utilization (kB).

CCSC: Compressed class space capacity (kB).

CCSU: Compressed class space used (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 option
Old generation size statistics.

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.

-gcmetacapacity option
Metaspace size statistics.

MCMN: Minimum metaspace capacity (kB).

MCMX: Maximum metaspace capacity (kB).

MC: Metaspace capacity (kB).

CCSMN: Compressed class space minimum capacity (kB).

CCSMX: Compressed class space maximum 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 option
Summary of garbage collection statistics.

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.

-printcompilation option
Java HotSpot VM compiler method statistics.

Compiled: Number of compilation tasks performed by the most
recently compiled method.

Size: Number of bytes of byte code of the most recently compiled
method.

Type: Compilation type of the most recently compiled method.

Method: Class name and method name identifying the most recently
compiled method. Class name uses slash (/) instead of dot (.) as a
name space separator. Method name is the method within the
specified class. The format for these two fields is consistent with
the HotSpot -XX:+PrintCompilation option.

EXAMPLES
This section presents some examples of monitoring a local JVM with an
lvmid of 21891.

The gcutil Option
This example attaches to lvmid 21891 and takes 7 samples at 250
millisecond intervals and displays the output as specified by the
-gcutil option.

The output of this example shows that a young generation collection
occurred between the third and fourth sample. The collection took 0.078
seconds and promoted objects from the eden space (E) to the old space
(O), resulting in an increase of old space utilization from 66.80% to
68.19%. Before the collection, the survivor space was 97.02% utilized,
but after this collection it is 91.03% utilized.

jstat -gcutil 21891 250 7
S0 S1 E O M CCS YGC YGCT FGC FGCT GCT
0.00 97.02 70.31 66.80 95.52 89.14 7 0.300 0 0.000 0.300
0.00 97.02 86.23 66.80 95.52 89.14 7 0.300 0 0.000 0.300
0.00 97.02 96.53 66.80 95.52 89.14 7 0.300 0 0.000 0.300
91.03 0.00 1.98 68.19 95.89 91.24 8 0.378 0 0.000 0.378
91.03 0.00 15.82 68.19 95.89 91.24 8 0.378 0 0.000 0.378
91.03 0.00 17.80 68.19 95.89 91.24 8 0.378 0 0.000 0.378
91.03 0.00 17.80 68.19 95.89 91.24 8 0.378 0 0.000 0.378

Repeat the Column Header String
This example attaches to lvmid 21891 and takes samples at 250
millisecond intervals and displays the output as specified by -gcnew
option. In addition, it uses the -h3 option to output the column header
after every 3 lines of data.

In addition to showing the repeating header string, this example shows
that between the second and third samples, a young GC occurred. Its
duration was 0.001 seconds. The collection found enough active data
that the survivor space 0 utilization (S0U) would have exceeded the
desired survivor Size (DSS). As a result, objects were promoted to the
old generation (not visible in this output), and the tenuring threshold
(TT) was lowered from 31 to 2.

Another collection occurs between the fifth and sixth samples. This
collection found very few survivors and returned the tenuring threshold
to 31.

jstat -gcnew -h3 21891 250
S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT
64.0 64.0 0.0 31.7 31 31 32.0 512.0 178.6 249 0.203
64.0 64.0 0.0 31.7 31 31 32.0 512.0 355.5 249 0.203
64.0 64.0 35.4 0.0 2 31 32.0 512.0 21.9 250 0.204
S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT
64.0 64.0 35.4 0.0 2 31 32.0 512.0 245.9 250 0.204
64.0 64.0 35.4 0.0 2 31 32.0 512.0 421.1 250 0.204
64.0 64.0 0.0 19.0 31 31 32.0 512.0 84.4 251 0.204
S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT
64.0 64.0 0.0 19.0 31 31 32.0 512.0 306.7 251 0.204

Include a Time Stamp for Each Sample
This example attaches to lvmid 21891 and takes 3 samples at 250
millisecond intervals. The -t option is used to generate a time stamp
for each sample in the first column.

The Timestamp column reports the elapsed time in seconds since the
start of the target JVM. In addition, the -gcoldcapacity output shows
the old generation capacity (OGC) and the old space capacity (OC)
increasing as the heap expands to meet allocation or promotion demands.
The old generation capacity (OGC) has grown from 11,696 kB to 13,820 kB
after the eighty-first full garbage collection (FGC). The maximum
capacity of the generation (and space) is 60,544 kB (OGCMX), so it
still has room to expand.

Timestamp OGCMN OGCMX OGC OC YGC FGC FGCT GCT
150.1 1408.0 60544.0 11696.0 11696.0 194 80 2.874 3.799
150.4 1408.0 60544.0 13820.0 13820.0 194 81 2.938 3.863
150.7 1408.0 60544.0 13820.0 13820.0 194 81 2.938 3.863

Monitor Instrumentation for a Remote JVM
This example attaches to lvmid 40496 on the system named remote.domain
using the -gcutil option, with samples taken every second indefinitely.

The lvmid is combined with the name of the remote host to construct a
vmid of 40496@remote.domain. This vmid results in the use of the rmi
protocol to communicate to the default jstatd server on the remote
host. The jstatd server is located using the rmiregistry command on
remote.domain that is bound to the default port of the rmiregistry
command (port 1099).

jstat -gcutil 40496@remote.domain 1000
… output omitted

SEE ALSO

· java

· jps

· jstatd

· rmiregistry

JDK 8 03 March 2015 jstat

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