jstat(1)jstat(1)NAMEjstat - Java Virtual Machine statistics monitoring tool
SYNOPSISjstat [ 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 Win‐
dows 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]
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.
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 Man‐
ager.
hostname A hostname or IP address indicating the target host. If
hostname is omitted, then the target host is the local
host.
port The default port for communicating with the remote
server. If the hostname is omitted or the protocol spec‐
ifies 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.
servername The treatment of this parameter depends on implementa‐
tion. 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.
PARAMETERS
generalOption A single general command-line option (-help, -options,
or -version)
outputOptions One or more output options, consisting of a single
statOption, plus any of the -t, -h, and -J options.
vmid Virtual machine identifier, a string indicating the tar‐
get Java virtual machine (JVM). The general syntax is
[protocol:][//]lvmid[@hostname[:port]/servername
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.
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.
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.
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 for‐
mat 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.
-help Display help message.
-version Display version information.
-options Display list of statistics options. See the Output
Options section below.
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 out‐
put 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 gen‐
eral, 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 varia‐
tion 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.
-statOption Determines the statistics information that jstat dis‐
plays. The following table lists the available options.
Use the -options general option to display the list of
options for a particular platform installation.
┌─────────────────┬──────────────────────────────────────────────────────┐
│ Option │ Displays... │
├─────────────────┼──────────────────────────────────────────────────────┤
│class │ Statistics on the behavior of the class loader │
│compiler │ Statistics on the behavior of the HotSpot Just-In- │
│ │ Time compiler │
│gc │ Statistics on the behavior of the garbage collected │
│ │ heap │
│gccapacity │ Statistics of the capacities of the generations and │
│ │ their corresponding spaces. │
│gccause │ Summary of garbage collection statistics (same as │
│ │ -gcutil), with the cause of the last and current (if │
│ │ applicable) garbage collection events. │
│gcnew │ Statistics of the behavior of the new generation. │
│gcnewcapacity │ Statistics of the sizes of the new generations and │
│ │ its corresponding spaces. │
│gcold │ Statistics of the behavior of the old and permanent │
│ │ generations. │
│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. │
└─────────────────┴──────────────────────────────────────────────────────┘
-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.
-t n Display a timestamp column as the first column of out‐
put. The timestamp is the the time since the start time
of the target JVM.
-JjavaOption Pass javaOption to the java application launcher. For
example, -J-Xms48m sets the startup memory to 48
megabytes. For a complete list of options, see java(1).
STATOPTIONS AND OUTPUT
The following tables summarize the columns that jstat outputs for each
statOption.
class Class Loader Statistics
┌─────────┬────────────────────────────────────────────────────────┐
│ 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 │
└─────────┴────────────────────────────────────────────────────────┘
compiler
HotSpot Just-In-Time Compiler Statistics
┌─────────────┬───────────────────────────────────────────────────────┐
│ 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 │
└─────────────┴───────────────────────────────────────────────────────┘
gc Garbage-collected heap statistics
┌───────┬───────────────────────────────────────────┐
│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. │
└───────┴───────────────────────────────────────────┘
gccapacity
Memory Pool Generation and Space Capacities
┌───────┬─────────────────────────────────────────────┐
│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. │
└───────┴─────────────────────────────────────────────┘
gccause
This option displays the same summary of garbage collection sta‐
tistics 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:
┌───────┬──────────────────────────────────────┐
│Column │ Description │
├───────┼──────────────────────────────────────┤
│LGCC │ Cause of last Garbage Collection. │
│GCC │ Cause of current Garbage Collection. │
└───────┴──────────────────────────────────────┘
gcnew New Generation Statistics
┌───────┬───────────────────────────────────────────┐
│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. │
└───────┴───────────────────────────────────────────┘
gcnewcapacity
New Generation Space Size Statistics
┌───────┬─────────────────────────────────────────┐
│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. │
└───────┴─────────────────────────────────────────┘
gcold Old and Permanent Generation Statistics
┌───────┬────────────────────────────────────────┐
│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. │
└───────┴────────────────────────────────────────┘
gcoldcapacity
Old Generation Statistics
┌───────┬───────────────────────────────────────┐
│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. │
└───────┴───────────────────────────────────────┘
gcpermcapacity
Permanent Generation Statistics
┌───────┬─────────────────────────────────────────────┐
│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. │
└───────┴─────────────────────────────────────────────┘
gcutil Summary of Garbage Collection Statistics
┌───────┬───────────────────────────────────────────┐
│Column │ Description │
├───────┼───────────────────────────────────────────┤
│S0 │ Survivor space 0 utilization as a per‐ │
│ │ centage of the space's current capacity. │
│S1 │ Survivor space 1 utilization as a per‐ │
│ │ centage 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 percent‐ │
│ │ age 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 Compiler Method Statistics
┌─────────┬─────────────────────────────────────────────┐
│ 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:+PrintCom‐ │
│ │ plation option. │
└─────────┴─────────────────────────────────────────────┘
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 mil‐
lisecond 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
The output of this example shows that a young generation collection
occurred between the 3rd and 4th sample. The collection took 0.001 sec‐
onds 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 millisec‐
ond 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
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 sur‐
vivor space 0 utilization (S0U) would would have exceeded the desired
survivor Size (DSS). As a result, objects were promoted to the old gen‐
eration (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 collec‐
tion 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 mil‐
lisecond 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
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.
jstat-gcutil 40496@remote.domain 1000
... output omitted
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 ALSOjava(1)jps(1)jstatd(1)rmiregistry(1)
13 June 2004 jstat(1)
