jstat

jstat(1)                                                              jstat(1)



NAME
       jstat - Java Virtual Machine Statistics Monitoring Tool

SYNOPSIS
       jstat [ generalOption | outputOptionsvmid [interval[s|ms] [count]] ]

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 target Java vir‐
          tual 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 pro‐
          tocol, 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 millisec‐
          onds (ms). Default units are milliseconds.  Must be a positive inte‐
          ger.  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  host‐
          name  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 Win‐
          dows 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  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 implementation. For the
          optimized local protocol, this field is ignored. For the rmi  proto‐
          col,  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 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 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  fol‐
          lowing  table lists the available options.  Use the -options general
          option to display the list of  options  for  a  particular  platform
          installation.


       -hn
          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.

       -tn
          Display  a timestamp column as the first column of output. The time‐
          stamp 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 the following documents:

          * java - the Java application launcher (Solaris) @
            http://java.sun.com/javase/6/docs/tech‐
            notes/tools/solaris/java.html

          * java - the Java application launcher (Linux) @
            http://java.sun.com/javase/6/docs/technotes/tools/linux/java.html

          * java - the Java application launcher (Windows)

   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

       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
          * java - the Java Application Launcher

          * jps - the Java Process Status Application

          * jstatd - the jvmstat daemon

          * rmiregistry - the Java Remote Object Registry




                                  06 Aug 2006                         jstat(1)