jstat - Unix, Linux Command
NAME
jstat - Java Virtual Machine statistics monitoring tool
SYNOPSIS
jstat [ generalOption | outputOptions vmid [interval[s|ms] [count]] ] DESCRIPTION
The
jstat tool displays performance statistics for an instrumented
HotSpot Java virtual machine (JVM). The target JVM is identified by
its virtual machine identifier, or vmid option described below.
NOTE - This utility is unsupported and may or may not be
available in future versions of the J2SE SDK.
It is currently not available on Windows 98 and Windows ME platforms.
VIRTUAL MACHINE IDENTIFIER
The syntax of the vmid string largely corresponds to the syntax of a URI:
[protocol:][//]lvmid[@hostname][:port][/servername]
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| Tag | Description |
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protocol |
The communications protocol. If the protocol is omitted and a hostname is not specified, the default protocol is a platform specific optimized
local protocol. If the protocol is omitted and a hostname is specified, then the default protocol is rmi.
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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 lvmid on Unix platforms
with the ps command, and on Windows with the Windows Task Manager.
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hostname |
A hostname or IP address indicating the target host. If hostname is omitted, then the target host is the local host.
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port |
The default port for communicating with the remote server. If the hostname is omitted or the protocol specifies an optimized, local protocol,
then port is ignored. Otherwise, treatment of the port parameter is implementation specific. For the default rmi protocol, the port indicates the
port number for the rmiregistry on the remote host. If port is omitted, and protocol indicates rmi, then the default rmiregistry port (1099) is
used.
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servername |
The treatment of this 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.
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PARAMETERS
| Tag | Description |
|---|
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generalOption |
A single general command-line option (-help, -options, or -version)
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outputOptions |
One or more output options, consisting of a single statOption,
plus any of the -t, -h, and -J options.
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vmid |
Virtual machine identifier, a string indicating the target Java virtual machine (JVM). The general syntax is
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| Tag | Description |
|---|
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[protocol:][//]lvmid[@hostname[:port]/servername
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The syntax of the vmid string largely corresponds to the syntax of a URI. The vmid can vary from a simple integer representing a local JVM to a
more complex construction specifying a communications protocol, port number, and other implementation-specific values. See Virtual Machine
Identifier below for details.
| Tag | Description |
|---|
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interval[s|ms] |
Sampling interval in the specified units, seconds (s) or milliseconds (ms). Default units are milliseconds. Must be a positive integer. If specified,
jstat will produce its output at each interval.
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count |
Number of samples to display. Default value is infinity; that is, jstat displays statistics until the target JVM terminates or the jstat command is
terminated. Must be a positive integer.
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OPTIONS
The
jstat command supports two types of options, general options and output options.
General options cause jstat to display simple
usage and version information. Output options determine the
content and format of the statistical output.
NOTE- All options, and their functionality are subject to change or removal in future releases.
GENERAL OPTIONS
If you specify one of the general options, you cannot specify any other option or parameter.
| Tag | Description |
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-help |
Display help message.
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-version |
Display version information.
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-options |
Display list of statistics options. See the Output Options section below.
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OUTPUT OPTIONS
If you do not specify a general option, then you can specify output options.
Output options determine the content and format of jstat’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 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 generally consistent between the different
options. In general, if two options provide a column with the same
name, then the data source for the two columns are 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 startup of the target JVM. 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, jstat displays its output.
NOTE- You are advised not to write scripts to parse jstat’s output since
the format may change in future releases. If you choose to write
scripts that parse jstat output, expect to modify them for future
releases of this tool.
| Tag | Description |
|---|
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-statOption |
Determines the statistics information that jstat displays. The following
table lists the available options. Use the -options general option to
display the list of options for a particular platform installation.
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| Option | Displays... |
| class | Statistics on the behavior of the class loader |
| compiler | Statistics on the behavior of the HotSpot
Just-In-Time compiler
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| gc | Statistics on the behavior of the garbage
collected heap
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| gccapacity | Statistics of the capacities of the
generations and their corresponding spaces.
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| gccause | Summary of garbage collection statistics (same
as -gcutil), with the cause of the last and
current (if applicable) garbage collection events.
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| gcnew | Statistics of the behavior of the new generation. |
| gcnewcapacity | Statistics of the sizes of the new generations
and its corresponding spaces.
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| gcold | Statistics of the behavior of the old and
permanent generations.
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| gcoldcapacity | Statistics of the sizes of the old generation. |
| gcpermcapacity | Statistics of the sizes of the permanent generation. |
| gcutil | Summary of garbage collection statistics. |
| printcompilation | Summary of garbage collection statistics. |
| Tag | Description |
|---|
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-h n |
Display a column header every n samples (output rows), where n is a
positive integer. Default value is 0, which displays the column header
above the first row of data.
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-t n |
Display a timestamp column as the first column of output. The timestamp
is the the time since the start time of the target JVM.
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-JjavaOption
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Pass javaOption to the java application launcher. For example, --Xms48m
sets the startup memory to 48 megabytes. For a complete list of
options, see java(1).
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STATOPTIONS AND OUTPUT
The following tables summarize the columns that jstat outputs
for each statOption.
| Tag | Description |
|---|
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-class Option |
Class Loader Statistics
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| Column | Description |
| Loaded | Number of classes loaded |
| Bytes | Number of Kbytes loaded |
| Unloaded | Number of classes unloaded |
| Bytes | Number of Kbytes unloaded |
| Time | Time spent performing class load and unload operations |
| Tag | Description |
|---|
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-compiler Option |
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HotSpot Just-In-Time Compiler Statistics
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| Column | Description |
| Compiled | Humber of compilation tasks performed |
| Failed | Number of compilation tasks that 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 for the last failed compilation |
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-gc Option |
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Garbage-collected heap statistics
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| Column | Description |
| SOC | 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). |
| PC | Current permanent space capacity (KB). |
| PU | Permanent space utilization (KB). |
| 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. |
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-gccapacity Option |
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Memory Pool Generation and Space Capacities
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| Column | Description |
| 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). |
| PGCMN | Minimum permanent generation capacity (KB). |
| PGCMX | Maximum Permanent generation capacity (KB). |
| PGC | Current Permanent generation capacity (KB). |
| PC | Current Permanent space capacity (KB). |
| VGC | Number of Young generation GC Events. |
| FGC | Number of Full GC Events. |
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-gccause Option |
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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 (if applicable) the current garbage collection
event. In addition to the columns listed for -gcutil, this option adds
the following columns:
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| Column | Description |
| LGCC | Cause of last Garbage Collection. |
| GCC | Cause of current Garbage Collection. |
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-gcnew Option |
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New Generation Statistics
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| Column | Description |
| SOC | 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). |
| VGC | Number of young generation GC events. |
| VGCT | Young generation garbage collection time. |
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-gcnewcapacity Option |
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New Generation Space Size Statistics
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| Column | Description |
| 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. |
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-gcold Option |
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Old and Permanent Generation Statistics
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| Column | Description |
| 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. |
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-gcoldcapacity Option |
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Old Generation Statistics
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| Column | Description |
| OGCMN | Minimum old generation capacity (KB). |
| OGCMV | 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. |
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-gcpermcapacity Option |
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Permanent Generation Statistics
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| Column | Description |
| 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. |
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-gcutil Option |
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Summary of Garbage Collection Statistics
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| Column | Description |
| S0 | Survivor space 0 utilization as a percentage
of the space’s current capacity.
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| S1 | Survivor space 1 utilization as a percentage
of the space’s current capacity.
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| E | Eden space utilization as a percentage
of the space’s current capacity.
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| O | Old space utilization as a percentage
of the space’s current capacity.
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| P | Permanent space utilization as a percentage
of the space’s current capacity.
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| 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. |
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-printcompilation Option |
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HotSpot Compiler Method Statistics
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| Column | Description |
| Compiled | Number of compilation tasks performed. |
| Size | Number of bytes of bytecode for the method. |
| Type | Compilation type. |
| Method | Class name and method name identifying the compiled method. Class name uses "/" instead of "." as namespace separator. Method name is the method within the given class. The format for these two fields is consistent with the HotSpot - XX:+PrintComplation option.
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EXAMPLES
This section presents some examples of monitoring a local JVM
with a lvmid of 21891.
Using 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.
jstat -gcutil 21891 250 7
S0 S1 E O P YGC YGCT FGC FGCT GCT
12.44 0.00 27.20 9.49 96.70 78 0.176 5 0.495 0.672
12.44 0.00 62.16 9.49 96.70 78 0.176 5 0.495 0.672
12.44 0.00 83.97 9.49 96.70 78 0.176 5 0.495 0.672
0.00 7.74 0.00 9.51 96.70 79 0.177 5 0.495 0.673
0.00 7.74 23.37 9.51 96.70 79 0.177 5 0.495 0.673
0.00 7.74 43.82 9.51 96.70 79 0.177 5 0.495 0.673
0.00 7.74 58.11 9.51 96.71 79 0.177 5 0.495 0.673
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The output of this example shows that a young generation collection
occurred between the 3rd and 4th sample. The collection took
0.001 seconds and promoted objects from the eden space (E) to the
old space (O), resulting in an increase of old space utilization from
9.49% to 9.51%. Before the collection, the survivor space was
12.44% utilized, but after this collection it is only 7.74% utilized.
Repeating the column header string
This example attaches to lvmid 21891 and takes samples at 250
millisecond intervals and displays the output as specified by -gcutil
option. In addition, it uses the -h3 option to output the column
header after every 3 lines of data.
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
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In addition to showing the repeating header string, this example
shows that between the 2nd and 3rd samples, a young GC occurred. Its
duration was 0.001 seconds. The collection found enough live data that
the survivor space 0 utilization (S0U) would 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 5th and 6th samples. This
collection found very few survivors and returned the tenuring
threshold to 31.
Including 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.
jstat -gcoldcapacity -t 21891 250 3
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
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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 on
remote.domain that is bound to the default rmiregistry port (port 1099).
SEE ALSO
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