jmap显示堆内存

秒速五厘米 2022-09-07 05:55 182阅读 0赞

# 一 点睛 #

> jmap -heap pid
> 
> jmap -histo pid

# 二 实战 #

## 1 代码 ##

package chaper02;
    
    import java.util.ArrayList;
    
    /**
    * -Xms60m -Xmx60m -XX:SurvivorRatio=8
    * 老年代：40m
    * 伊甸园：16m
    * s0:2m
    * s1:2m
    */
    public class GCTest {
        public static void main(String[] args) {
            ArrayList<byte[]> list = new ArrayList<>();
            for (int i = 0; i < 1000; i++) {
                byte[] arr = new byte[1024 * 100];// 100KB
                list.add(arr);
                try {
                    Thread.sleep(120);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

## 2 测试—— jmap -heap pid ##

F:\svn\19_byzb_back\branches\JVMDemo3>jmap -heap 18220
    Attaching to process ID 18220, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 25.251-b08
    
    using thread-local object allocation.
    Parallel GC with 8 thread(s)
    
    Heap Configuration:
       MinHeapFreeRatio         = 0
       MaxHeapFreeRatio         = 100
       MaxHeapSize              = 62914560 (60.0MB)
       NewSize                  = 20971520 (20.0MB)
       MaxNewSize               = 20971520 (20.0MB)
       OldSize                  = 41943040 (40.0MB)
       NewRatio                 = 2
       SurvivorRatio            = 8
       MetaspaceSize            = 21807104 (20.796875MB)
       CompressedClassSpaceSize = 1073741824 (1024.0MB)
       MaxMetaspaceSize         = 17592186044415 MB
       G1HeapRegionSize         = 0 (0.0MB)
    
    Heap Usage:
    PS Young Generation
    Eden Space:
       capacity = 16777216 (16.0MB)
       used     = 518960 (0.4949188232421875MB)
       free     = 16258256 (15.505081176757812MB)
       3.093242645263672% used
    From Space:
       capacity = 2097152 (2.0MB)
       used     = 2068752 (1.9729156494140625MB)
       free     = 28400 (0.0270843505859375MB)
       98.64578247070312% used
    To Space:
       capacity = 2097152 (2.0MB)
       used     = 0 (0.0MB)
       free     = 2097152 (2.0MB)
       0.0% used
    PS Old Generation
       capacity = 41943040 (40.0MB)
       used     = 12691296 (12.103363037109375MB)
       free     = 29251744 (27.896636962890625MB)
       30.258407592773438% used
    
    3137 interned Strings occupying 257872 bytes.

## 3 测试——jmap -histo pid ##

F:\svn\19_byzb_back\branches\JVMDemo3>jmap -histo 18220
    
    
    num     #instances         #bytes  class name
    ----------------------------------------------
       1:           706       29426648  [B
       2:          4528         433360  [C
       3:           224         187592  [I
       4:          4379         105096  java.lang.String
    ......
    264:             1             16  sun.util.locale.provider.SPILocaleProviderAdapter
    265:             1             16  sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter
    266:             1             16  sun.util.resources.LocaleData
    267:             1             16  sun.util.resources.LocaleData$LocaleDataResourceBundleControl
    Total         15407       30457216