jstat tool

Displaying GC Statistics

Use the -gc option to display garbage collection-related statistics:

jstat -gc <PID>

Sample output:

 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC      MU    CCSC   CCSU      YGC   YGCT   FGC    FGCT    GCT
 1024.0 1024.0  0.0   512.0   8192.0   4096.0   20480.0    10240.0   3200.0  1600.0 512.0  256.0       5    0.100    2      0.200  0.300

Field explanations:

• S0C / S1C: Capacity of Survivor 0 and Survivor 1 spaces in the young generation Eden space (KB).
• S0U / S1U: Used space in Survivor 0 and Survivor 1 spaces in the young generation Eden space (KB).
• EC: Capacity of the Eden space in the young generation (KB).
• EU: Used space in the Eden space in the young generation (KB).
• OC: Capacity of the old generation (KB).
• OU: Used space in the old generation (KB).
• MC: Capacity of the Metaspace (KB).
• MU: Used space in the Metaspace (KB).
• CCSC: Capacity of the compressed class space (KB).
• CCSU: Used space in the compressed class space (KB).
• YGC: Number of young generation GCs.
• YGCT: Time spent on young generation GCs (seconds).
• FGC: Number of old generation GCs.
• FGCT: Time spent on old generation GCs (seconds).
• GCT: Total time spent on GCs (seconds).

Displaying Class Loading Statistics

Use the -class option to display class loading-related statistics:

jstat -class <PID>

Sample output:

Loaded  Bytes  Unloaded  Bytes   Time
  1024  512000      100   50000   0.50

Field explanations:

• Loaded: Number of classes loaded.
• Bytes: Bytes occupied by loaded classes.
• Unloaded: Number of classes unloaded.
• Bytes: Bytes freed by unloaded classes.
• Time: Total time spent on class loading and unloading (seconds).

Displaying Compiler Statistics

Use the -compiler option to display JIT compiler-related statistics:

jstat -compiler <PID>

Sample output:

Compiled  Failed  Invalid  Time  FailedType  FailedMethod
   2048      2       0    15.00     1       MyClass::myMethod

Field explanations:

• Compiled: Number of methods compiled.
• Failed: Number of methods that failed to compile.
• Invalid: Number of invalid compilations.
• Time: Total time spent on compilation (seconds).
• FailedType: Type of the last compilation failure.
• FailedMethod: Name of the method that failed last to compile.

Displaying GC Utilization Statistics

Use the -gcutil option to display garbage collection-related memory utilization:

jstat -gcutil <PID>

Sample output:

  S0     S1     E      O      M     CCS   YGC   YGCT   FGC    FGCT     GCT
  0.0   50.0   25.0  50.0   50.0  50.0     5    0.100   2     0.200   0.300

Field explanations:

• S0 / S1: Memory utilization of Survivor 0 and Survivor 1 spaces in the young generation Eden space (%).
• E: Memory utilization of the Eden space in the young generation (%).
• O: Memory utilization of the old generation (%).
• M: Memory utilization of the Metaspace (%).
• CCS: Memory utilization of the compressed class space (%).
• YGC: Number of young generation GCs.
• YGCT: Time spent on young generation GCs (seconds).
• FGC: Number of old generation GCs.
• FGCT: Time spent on old generation GCs (seconds).
• GCT: Total time spent on GCs (seconds).

Displaying Memory Area Capacity and Usage

Use the -gccapacity option to display the capacity and usage of memory areas (such as young generation, old generation, and permanent generation):

jstat -gccapacity <PID>

Sample output:

 NGCMN    NGCMX     NGC     S0C     S1C     EC      OGCMN    OGCMX     OGC      OC       CCNM     CCNX    CCMX     CCSMN   CCSMX     CCSC     CCSU
  2048.0  8192.0  4096.0   512.0   512.0   3072.0  10240.0  20480.0  15360.0  10240.0  1024.0  2048.0  3072.0  1024.0  2048.0  1536.0   1024.0

Field explanations:

• NGCMN: Minimum capacity of the young generation (KB).
• NGCMX: Maximum capacity of the young generation (KB).
• NGC: Current capacity of the young generation (KB).
• S0C / S1C: Capacity of Survivor 0 and Survivor 1 spaces in the young generation Eden space (KB).
• EC: Capacity of the Eden space in the young generation (KB).
• OGCMN: Minimum capacity of the old generation (KB).
• OGCMX: Maximum capacity of the old generation (KB).
• OGC: Current capacity of the old generation (KB).
• OC: Capacity of the old generation (KB).
• CCNM / CCNX: Minimum and maximum capacities of the compressed class space (KB).
• CCMX: Current capacity of the compressed class space (KB).
• CCSMN / CCSMX: Minimum and maximum capacities of the compressed class space (KB).
• CCSC: Capacity of the compressed class space (KB).
• CCSU: Used space in the compressed class space (KB).

Displaying Metaspace Capacity and Usage

Use the -gcmetacapacity option to display the capacity and usage of the JVM metadata area (Metaspace):

jstat -gcmetacapacity <PID>

Sample output:

 MC       MU      CCSC    CCSU
  3200.0  1600.0  512.0  256.0

Field explanations:

• MC: Capacity of the Metaspace (KB).
• MU: Used space in the Metaspace (KB).
• CCSC: Capacity of the compressed class space (KB).
• CCSU: Used space in the compressed class space (KB).