gclogの分析方法

一、概要
GCのLOGでもメモリ漏洩の判断に関する情報が提供されます.
 
二、例説明
漏れのあるプログラムを書く.

package net.dncsoft;

import java.util.ArrayList;
import java.util.List;

public class MainGCTest {
	public static void main(String[] args) throws Exception {
		byte[] buf = null;
		List<byte[]> bufList = new ArrayList<byte[]>();
		long counter = 0;
		while (true) {
			buf = new byte[1024 * 1024];
			bufList.add(buf);
			Thread.sleep(1000);
			System.out.println(counter++);
		}
	}
}

 
三、次のコマンドを実行します.

java -Xmx16m -Xms16m -XX:NewSize=4m -XX:MaxNewSize=4m -Xloggc:./gc.txt -XX:+PrintGCDetails net.dncsoft.MainGCTest

 
四、このGCLogファイルを手に入れます.

2.119: [GC 2.119: [DefNew: 2314K->148K(3712K), 0.0046925 secs] 2314K->2196K(16000K), 0.0047737 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
5.127: [GC 5.127: [DefNew: 3258K->148K(3712K), 0.0049901 secs] 5306K->5268K(16000K), 0.0050748 secs] [Times: user=0.00 sys=0.01, real=0.02 secs] 
8.135: [GC 8.135: [DefNew: 3245K->148K(3712K), 0.0050552 secs] 8365K->8340K(16000K), 0.0051423 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
11.144: [GC 11.144: [DefNew: 3236K->148K(3712K), 0.0054953 secs] 11429K->11413K(16000K), 0.0055777 secs] [Times: user=0.00 sys=0.02, real=0.02 secs] 
14.152: [GC 14.152: [DefNew: 3231K->3231K(3712K), 0.0000191 secs]14.153: [Tenured: 11264K->11264K(12288K), 0.0180049 secs] 14495K->14485K(16000K), [Perm : 291K->291K(12288K)], 0.0181553 secs] [Times: user=0.02 sys=0.00, real=0.01 secs] 
14.171: [Full GC 14.171: [Tenured: 11264K->11264K(12288K), 0.0124251 secs] 14485K->14471K(16000K), [Perm : 291K->286K(12288K)], 0.0125105 secs] [Times: user=0.01 sys=0.00, real=0.02 secs] 
Heap
 def new generation   total 3712K, used 3280K [0x319e0000, 0x31de0000, 0x31de0000)
  eden space 3328K,  98% used [0x319e0000, 0x31d14358, 0x31d20000)
  from space 384K,   0% used [0x31d20000, 0x31d20000, 0x31d80000)
  to   space 384K,   0% used [0x31d80000, 0x31d80000, 0x31de0000)
 tenured generation   total 12288K, used 11264K [0x31de0000, 0x329e0000, 0x329e0000)
   the space 12288K,  91% used [0x31de0000, 0x328e00b0, 0x328e0200, 0x329e0000)
 compacting perm gen  total 12288K, used 286K [0x329e0000, 0x335e0000, 0x369e0000)
   the space 12288K,   2% used [0x329e0000, 0x32a279d0, 0x32a27a00, 0x335e0000)
    ro space 10240K,  51% used [0x369e0000, 0x36f0baf8, 0x36f0bc00, 0x373e0000)
    rw space 12288K,  54% used [0x373e0000, 0x37a776d8, 0x37a77800, 0x37fe0000)