java - 解释 jstat 结果

Question

我是 jstat 工具的新手。因此，我做了如下示例。

./jstat -gcutil -t 4001 5000
Timestamp         S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT
       565088.4   0.00   0.89  75.86  40.59  84.80    405    3.822     4    0.549    4.371
       565093.4   0.00   0.89  77.81  40.59  84.80    405    3.822     4    0.549    4.371
       565098.4   0.00   0.89  77.81  40.59  84.80    405    3.822     4    0.549    4.371
       565103.5   0.00   0.89  77.85  40.59  84.80    405    3.822     4    0.549    4.371
       565108.5   0.00   0.89  77.85  40.59  84.80    405    3.822     4    0.549    4.371
       565113.4   0.00   0.89  77.85  40.59  84.80    405    3.822     4    0.549    4.371


jstat -gc output

 S0C    S1C    S0U    S1U      EC       EU        OC         OU       PC     PU    YGC     YGCT    FGC    FGCT     GCT
704.0  704.0   0.4    0.0    6080.0   4013.8   14928.0     6335.2   21248.0 18019.6    436    3.957   4      0.549    4.506
704.0  704.0   0.4    0.0    6080.0   4016.6   14928.0     6335.2   21248.0 18019.6    436    3.957   4      0.549    4.506
704.0  704.0   0.4    0.0    6080.0   4135.4   14928.0     6335.2   21248.0 18019.6    436    3.957   4      0.549    4.506
704.0  704.0   0.4    0.0    6080.0   4135.4   14928.0     6335.2   21248.0 18019.6    436    3.957   4      0.549    4.506
704.0  704.0   0.4    0.0    6080.0   4135.4   14928.0     6335.2   21248.0 18019.6    436    3.957   4      0.549    4.506
704.0  704.0   0.4    0.0    6080.0   4135.4   14928.0     6335.2   21248.0 18019.6    436    3.957   4      0.549    4.506

这个结果说明了什么？哪些是要注意可能的内存问题的列，例如内存泄漏等。

Answer 1

gcutil 以百分比利用率提供统计信息

-gcutil Option
Summary of Garbage Collection Statistics 
Column  Description
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.
P       Permanent space utilization as a percentage of the space's current capacity.
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.

gc 提供分配空间和使用空间方面的统计信息。

-gc Option
Garbage-collected heap statistics 
Column  Description
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).
PC      Current permanent space capacity (KB).
PU      Permanent space utilization (KB).
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.

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