Jstat command summary [easy to understand]

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jvm Statistical information monitoring tools

One 、 jstat What is it?

jstat yes JDK A lightweight gadget that comes with you . Full name “Java Virtual Machine statistics monitoring tool”, It is located in java Of bin Under the table of contents , Mainly used JVM Built in instructions for Java Real time command line monitoring of application resources and performance , Yes, yes. Heap size And garbage collection monitoring .

jstat It is a command line tool used to see various running state information of virtual machine . It can show class loading in local or remote virtual machine processes 、 Memory 、 garbage collection 、jit Compile and other operation data , It's online positioning jvm Preferred tool for performance .

Two 、 jstat Command format

jstat [ generalOption | outputOptions vmid [interval[s|ms] [count]] ]

• generalOption : Single common command line options , Such as -help, -options, or -version.
• outputOptions : One or more output options , By a single statOption Options make up , You can talk to -t, -h, and -J And so on .

Usage: jstat -help|-options
       jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]

Definitions:
  <option>      An option reported by the -options option( Optional parameters )
  <vmid>        Virtual Machine Identifier. A vmid takes the following form:
                     <lvmid>[@<hostname>[:<port>]]（ Identifier of the virtual machine ）
                Where <lvmid> is the local vm identifier for the target
                Java virtual machine, typically a process id; <hostname> is
                the name of the host running the target Java virtual machine;
                and <port> is the port number for the rmiregistry on the
                target host. See the jvmstat documentation for a more complete
                description of the Virtual Machine Identifier.
  <lines>       Number of samples between header lines.
  <interval>    Sampling interval. The following forms are allowed:
                    <n>["ms"|"s"]（ Sampling interval ： A hair | second ）
                Where <n> is an integer and the suffix specifies the units as
                milliseconds("ms") or seconds("s"). The default units are "ms".
  <count>       Number of samples to take before terminating.（ The number of samples to be taken before termination ）
  -J<flag>      Pass <flag> directly to the runtime system.

# option：  Parameter options 
# -t：  You can add... To the printed column Timestamp Column , It is used to display the running time of the system 
# -h：  It's possible to do this in the case of periodic data , You can output the header once after you specify how many lines to output 
# vmid： Virtual Machine ID（  Process  pid）
# interval：  The interval between each execution , The unit is millisecond 
# count：  Used to specify how many records to output , By default, it will always print 

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3、 ... and 、jstat Parameter options

> jstat -options

-class  Show ClassLoad Information about ; -compiler  Show JIT Information about compilation ; -gc  Display and gc Related heap information ; -gccapacity 　　  Shows the capacity and usage of each generation ; -gcmetacapacity  Show metaspace Size  -gcnew  Display the new generation information ; -gcnewcapacity  Show the size and usage of the new generation ; -gcold  Displays information about the elderly and permanent generations ; -gcoldcapacity  Show the size of the old age ; -gcutil　　  Show garbage collection information ; -gccause  Display information about garbage collection （ through -gcutil）, At the same time, it shows the inducement of the last or current garbage collection ; -printcompilation  Output JIT Compiled method information  

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Parameter name	Parameter description
class	Used to view the statistics of class loading , According to load class The number of , And the space occupied .
compiler	see HotSpot The statistics of compiler compilation in
gc	see JVM Statistics of garbage collection in the middle pile , Can be displayed gc Information about , see gc The number of times , And time . The last five of them , Namely young gc The number of times ,young gc Time for ,full gc The number of times ,full gc Time for ,gc The total time of .
gccapacity	Check out the new generation 、 Storage capacity of old generation and permanent generation , Can be displayed ,VM Three generations in memory （young,old,perm） Object usage and occupancy size
gccause	Check the statistics of garbage collection （ This and -gcutil Options as ）, If there is garbage collection , It also shows why garbage collection was last and is currently taking place
gcmetacapacity	Show about metaspace Statistics of size .
gcnew	Check out the new generation of garbage collection ,new Object information
gcnewcapacity	Used to view the storage capacity of the new generation ,new Object information and its usage
gcold	It is used to check the generation of the old generation and the generation of the permanent generation GC The situation of ,old Object information
gcoldcapacity	Used to check the capacity of the old generation ,old Object information and its usage
gcpermcapacity	Used to view the capacity of persistent generation ,perm Object information and its usage
gcutil	Check out the new generation 、 Garbage collection of the old generation and the old generation
printcompilation	At present VM Execution information

Four 、 Parameter usage example

#  Print out the result once on the screen 
> jstat -gccause pid

#  Constantly print out the results on the screen 
> jstat -gccause pid 1  Each grid 1 Millisecond output 
> jstat -gccause pid 2000  Each grid 2 Second output result 

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Class load statistics class

PS C:\>
PS C:\> jstat -class 6368
Loaded  Bytes  Unloaded  Bytes     Time
  1846  3621.2        0     0.0       0.98
PS C:\>

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• Loaded: load class The number of
• Bytes： The amount of space occupied
• Unloaded： Number of unloaded
• Bytes: Occupied space not loaded
• Time： Time

Compilation statistics compiler

PS C:\> jstat -compiler 6368
Compiled Failed Invalid   Time   FailedType FailedMethod
     791      0       0     1.17          0
PS C:\>

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• Compiled： Number of compilations
• Failed： The number of failures
• Invalid： Unavailable quantity
• Time： Time
• FailedType： Failure type
• FailedMethod： The way to fail

Compilation statistics compiler

Garbage collection statistics gc

PS C:\> jstat -gc 6368
 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT
5120.0 5120.0  0.0    0.0   32768.0  29858.7   86016.0      0.0     4480.0 770.3  384.0   75.9       0    0.000   0      0.000    0.000
PS C:\>

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• S0C： The size of the first surviving area
• S1C： The size of the second surviving area
• S0U： The size of the first surviving area
• S1U： The size of the second surviving area
• EC： The size of Eden Park
• EU： The use size of Eden Park
• OC： Old age size
• OU： Old age use size
• MC： Method area size
• MU： Method area usage size
• CCSC: Compress class space size
• CCSU: Compressed class space usage size
• YGC： Garbage collection times of young generation
• YGCT： Young generation garbage collection consumes time
• FGC： Recycling times in the old days
• FGCT： Garbage collection used time in the old days
• GCT： The total time spent in garbage collection

Heap memory statistics gccapacity

PS C:\> jstat -gccapacity 6368
 NGCMN    NGCMX     NGC     S0C   S1C       EC      OGCMN      OGCMX       OGC         OC       MCMN     MCMX      MC     CCSMN    CCSMX     CCSC    YGC    FGC
 43008.0 687104.0  43008.0 5120.0 5120.0  32768.0    86016.0  1375232.0    86016.0    86016.0      0.0 1056768.0   4480.0      0.0 1048576.0    384.0      0     0
PS C:\>

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• NGCMN： The minimum capacity of the new generation
• NGCMX： The largest capacity of the new generation
• NGC： Current Cenozoic capacity
• S0C： The size of the first surviving area
• S1C： The size of the second surviving area
• EC： The size of Eden Park
• OGCMN： The smallest capacity in the old days
• OGCMX： The biggest capacity in the old days
• OGC： The current size of the elderly
• OC: The current size of the elderly
• MCMN: Minimum metadata capacity
• MCMX： Maximum metadata capacity
• MC： Current metadata space size
• CCSMN： Minimum compressed class space size
• CCSMX： Maximum compressed class space size
• CCSC： Current compressed class space size
• YGC： The younger generation gc frequency
• FGC： Old age GC frequency

New generation garbage collection statistics gcnew

PS C:\> jstat -gcnew 6368
 S0C    S1C    S0U    S1U   TT MTT  DSS      EC       EU     YGC     YGCT
5120.0 5120.0    0.0    0.0 15  15    0.0  32768.0  29858.7      0    0.000
PS C:\>

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• S0C： The size of the first surviving area
• S1C： The size of the second surviving area
• S0U： The size of the first surviving area
• S1U： The size of the second surviving area
• TT: The number of times an object has survived in a new generation
• MTT: The maximum number of times an object has survived in a new generation
• DSS: The expected size of the surviving area
• EC： The size of Eden Park
• EU： The use size of Eden Park
• YGC： Garbage collection times of young generation
• YGCT： Young generation garbage collection consumes time

New generation memory statistics gcnewcapacity

PS C:\> jstat -gcnewcapacity 6368
  NGCMN      NGCMX       NGC      S0CMX     S0C     S1CMX     S1C       ECMX        EC      YGC   FGC
   43008.0   687104.0    43008.0 228864.0   5120.0 228864.0   5120.0   686080.0    32768.0     0     0
PS C:\>

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• NGCMN： The minimum capacity of the new generation
• NGCMX： The largest capacity of the new generation
• NGC： Current Cenozoic capacity
• S0CMX： The greatest survival 1 Area size
• S0C： The current survival 1 Area size
• S1CMX： The greatest survival 2 Area size
• S1C： The current survival 2 Area size
• ECMX： The largest Eden Park
• EC： The current size of Eden Park
• YGC： Garbage collection times of young generation
• FGC： Recovery times of the elderly

Old age garbage collection statistics gcold

PS C:\> jstat -gcold 6368
   MC       MU      CCSC     CCSU       OC          OU       YGC    FGC    FGCT     GCT
  4480.0    770.3    384.0     75.9     86016.0         0.0      0     0    0.000    0.000
PS C:\>

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• MC： Method area size
• MU： Method area usage size
• CCSC: Compress class space size
• CCSU: Compressed class space usage size
• OC： Old age size
• OU： Old age use size
• YGC： Garbage collection times of young generation
• FGC： Recycling times in the old days
• FGCT： Garbage collection used time in the old days
• GCT： The total time spent in garbage collection

Memory statistics in the old days

PS C:\> jstat -gcoldcapacity 6368
   OGCMN       OGCMX        OGC         OC       YGC   FGC    FGCT     GCT
    86016.0   1375232.0     86016.0     86016.0     0     0    0.000    0.000
PS C:\>

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• OGCMN： The smallest capacity in the old days
• OGCMX： The biggest capacity in the old days
• OGC： The current size of the elderly
• OC： Old age size
• YGC： Garbage collection times of young generation
• FGC： Recycling times in the old days
• FGCT： Garbage collection used time in the old days
• GCT： The total time spent in garbage collection

Metadata spatial statistics gcmetacapacity

PS C:\> jstat -gcmetacapacity 6368
   MCMN       MCMX        MC       CCSMN      CCSMX       CCSC     YGC   FGC    FGCT     GCT
       0.0  1056768.0     4480.0        0.0  1048576.0      384.0     0     0    0.000    0.000
PS C:\>

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• MCMN: Minimum metadata capacity
• MCMX： Maximum metadata capacity
• MC： Current metadata space size
• CCSMN： Minimum compressed class space size
• CCSMX： Maximum compressed class space size
• CCSC： Current compressed class space size
• YGC： Garbage collection times of young generation
• FGC： Recycling times in the old days
• FGCT： Garbage collection used time in the old days
• GCT： The total time spent in garbage collection

Summarize garbage collection statistics gcutil

PS C:\> jstat -gcutil 6368
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT
  0.00   0.00  91.12   0.00  17.19  19.76      0    0.000     0    0.000    0.000
PS C:\>

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• S0： survive 1 The current usage proportion of the zone
• S1： survive 2 The current usage proportion of the zone
• E： The use proportion of Eden Park
• O： The proportion used in the old age
• M： The usage ratio of metadata area
• CCS： Compress usage ratio
• YGC： Garbage collection times of young generation
• FGC： Recycling times in the old days
• FGCT： Garbage collection used time in the old days
• GCT： The total time spent in garbage collection

JVM Compilation method statistics

PS C:\> jstat -printcompilation 6368
Compiled  Size  Type Method 791 5510 1 com/sun/org/apache/xerces/internal/impl/XMLDocumentFragmentScannerImpl$FragmentContentDriver next PS C:\>

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• Compiled： Number of recently compiled methods
• Size： The number of bytecodes of the most recently compiled method
• Type： The compilation type of the recently compiled method .
• Method： Method name identification .

6、 ... and 、 Reference resources

jstat Command view jvm Of GC situation （ With Linux For example ）

jvm Optimization must know series —— Monitoring tools

One java Memory leak investigation case

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