JSTAT(1) JDK Commands JSTAT(1)
NAME
jstat - monitor JVM statistics
SYNOPSIS
Note: This command is experimental and unsupported.
jstat generalOptions
jstat outputOptions [-t] [-h lines] vmid [interval [count]]
generalOptions
A single general command-line option. See General Options.
outputOptions
An option reported by the -options option. One or more output
options that consist of a single statOption, plus any of the -t,
-h, and -J options. See Output Options for the jstat Command.
-t Displays a time-stamp column as the first column of output. The
time stamp is the time since the start time of the target JVM.
-h n Displays a column header every n samples (output rows), where n
is a positive integer. The default value is 0, which displays
the column header of the first row of data.
vmid A virtual machine identifier, which is a string that indicates
the target JVM. See Virtual Machine Identifier.
interval
The sampling interval in the specified units, seconds (s) or
milliseconds (ms). Default units are milliseconds. This must
be a positive integer. When specified, the jstat command pro-
duces its output at each interval.
count The number of samples to display. The default value is infini-
ty, 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.
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 can't specify any
other option or parameter.
-help Displays a help message.
-options
Displays a list of static options. See Output Options for the
jstat Command.
OUTPUT OPTIONS FOR THE JSTAT COMMAND
If you don't specify a general option, then you can specify output op-
tions. 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 spa-
ces. A header row with titles describes the columns. Use the -h op-
tion 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:
Don't write scripts to parse the jstat command's output because the
format might change in future releases. If you write scripts that
parse the jstat command output, then expect to modify them for future
releases of this tool.
-statOption
Determines the statistics information that 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 load-
er.
compiler: Displays statistics about the behavior of the Java
HotSpot VM Just-in-Time compiler.
gc: Displays statistics about the behavior of the garbage col-
lected heap.
gccapacity: Displays statistics about the capacities of the gen-
erations 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 about the behavior of the new genera-
tion.
gcnewcapacity: Displays statistics about the sizes of the new
generations and their corresponding spaces.
gcold: Displays statistics about the behavior of the old genera-
tion 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.
-JjavaOption
Passes javaOption to the Java application launcher. For exam-
ple, -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 KB loaded.
Unloaded: Number of classes unloaded.
Bytes: Number of KB unloaded.
Time: Time spent performing class loading and unloading opera-
tions.
-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 compila-
tion.
-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 Committed Size (KB).
MU: Metaspace utilization (KB).
CCSC: Compressed class committed size (KB).
CCSU: Compressed class space used (KB).
YGC: Number of young generation garbage collection (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 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 Committed Size (KB).
CCSMN: Compressed class space minimum capacity (KB).
CCSMX: Compressed class space maximum capacity (KB).
CCSC: Compressed class committed size (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 sta-
tistics 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 size statistics.
MC: Metaspace Committed Size (KB).
MU: Metaspace utilization (KB).
CCSC: Compressed class committed size (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 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 Committed Size (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 re-
cently 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 a slash (/) instead of a dot
(.) as a name space separator. The method name is the method
within the specified class. The format for these two fields is
consistent with the HotSpot -XX:+PrintCompilation option.
VIRTUAL MACHINE IDENTIFIER
The syntax of the vmid string corresponds to the syntax of a URI:
[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 proto-
col, port number, and other implementation-specific values.
protocol
The communications protocol. If the protocol value is omitted
and a host name isn't 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 provided the JVM processes is not running in a sepa-
rate docker instance. You can also determine the lvmid on Linux
and macOS platforms with the ps command, and on Windows with the
Windows Task Manager.
hostname
A host name 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. Oth-
erwise, treatment of the port parameter is implementation-spe-
cific. 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 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.
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 mil-
lisecond intervals and displays the output as specified by the -gcutil
option.
The output of this example shows that a young generation collection oc-
curred 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's 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 millisec-
ond 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 de-
sired 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 mil-
lisecond 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) in-
creasing 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 ca-
pacity 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's bound to the default port of the rmiregistry com-
mand (port 1099).
jstat -gcutil 40496@remote.domain 1000
... output omitted
JDK 21 2023 JSTAT(1)
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