jstat(1)jstat(1)Namejstat - Java Virtual Machine Statistics Monitoring Tool
SYNOPSISjstat [ generalOption | outputOptions vmid [interval[s|ms] [count]] ]
PARAMETERS
generalOption
A single general command-line option (-help, -options, or -ver‐
sion)
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 target 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 communica‐
tions protocol, port number, and other implementation-specific
values. See Virtual Machine Identifier for details.
interval[s|ms]
Sampling interval in the specified units, seconds (s) or mil‐
liseconds (ms). Default units are milliseconds. Must be a posi‐
tive 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.
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 not be available in future
versions of the JDK. It is not currently 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]
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 vir‐
tual machine identifier. The lvmid is typically, but not neces‐
sarily, the operating system's process identifier for the target
JVM process. You can use the jps(1) 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.
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 specifies an optimized, local
protocol, then port is ignored. Otherwise, treatment of the port
parameter is implementation specific. For the default rmi proto‐
col, 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 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 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.
-help
Display help message.
-version
Display version information.
-options
Display list of statistics options. See the Output Options sec‐
tion 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 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 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 displays. The
following table lists the available options. Use the -options
general option to display the list of options for a particular
platform installation.
-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 output. The
timestamp is 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 Option
-compiler Option
-gc Option
-gccapacity Option
-gccause Option
This option displays the same summary of garbage collection statistics
as the -gcutil option, but includes the causes of the last garbage col‐
lection event and (if applicable) the current garbage collection event.
In addition to the columns listed for -gcutil, this option adds the
following columns:
-gcnew Option
-gcnewcapacity Option
-gcold Option
-gcoldcapacity Option
-gcpermcapacity Option
-gcutil Option
-printcompilation 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
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 and/or promotion
demands. The old generation capacity (OGC) has grown to from 11696 KB
to 13820 KB after the 81st Full GC (FGC). The maximum capacity of the
generation (and space) is 60544 KB (OGCMX), so it still has room to
expand.
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
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
o java(1) - the Java Application Launcher
o jps(1) - the Java Process Status Application
o jstatd(1) - the jvmstat daemon
o rmiregistry(1) - the Java Remote Object Registry
16 Mar 2012 jstat(1)
