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Garbage Collection
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(Continued from previous part...)
I also tried to reach 7.5 MB, but failed:
java -Xms2m -Xmx8m GCTest 16 44 > tail_16_44.out
Time Total Free Free Total Act. Dead Over
sec. Mem. Mem. Per. Obj. Obj. Obj. Head
0 1984 1815 91% 0 0 0 169
0 1984 1682 84% 128 128 0 174
1 1984 1552 78% 256 256 0 176
....
20 5484 390 7% 4992 4992 0 102
20 5484 260 4% 5120 5120 0 104
21 8128 2780 34% 5248 5248 0 100
21 8128 2652 32% 5376 5376 0 100
....
51 8128 272 3% 7680 2432 5248 176
51 8128 270 3% 7680 2304 5376 178
52 8128 268 3% 7680 2176 5504 180
52 8128 266 3% 7680 2048 5632 182
53 8128 136 1% 7808 2176 5632 184
Exception in thread "main" java.lang.OutOfMemoryError
It is very interesting to see that the JVM died out of memory, but there
was 5632KB memory as garbage. Why did the JVM not collect
the garbages at that time?
Comparing with JDK 1.4.0, JDK 1.3.1 did a good job in collecting garbages.
JDK 1.3.1 allowed
GCTest to use upto 88% of the total memory, while JDK 1.4.0 crashed when GCTest
tring to get 63% of the total memory.
Comparison - Client vs. Server
I also made some tests to compare between the client version and the server
version of JDK 1.4.0.
java -server -Xms2m -Xmx8m GCTest 16 24 > tail_16_24.out
But the program ran out of memory the same way as the client version:
Time Total Free Free Total Act. Dead Over
sec. Mem. Mem. Per. Obj. Obj. Obj. Head
0 1984 1726 86% 0 0 0 258
0 1984 1593 80% 128 128 0 263
1 1984 1463 73% 256 256 0 265
....
19 5260 357 6% 4736 4736 0 167
19 5260 227 4% 4864 4864 0 169
20 8128 2997 36% 4992 4992 0 139
20 8128 2867 35% 5120 5120 0 141
21 8128 2866 35% 5120 4992 128 142
21 8128 2864 35% 5120 4864 256 144
....
41 8128 482 5% 7424 4352 3072 222
42 8128 352 4% 7552 4480 3072 224
42 8128 223 2% 7680 4608 3072 225
Exception in thread "main" java.lang.OutOfMemoryError
Comparison - JDK 1.6.0 vs. 1.4.0
After installing JDK 6u2 on a Windows XP system, I repeated the same tests to see
how JDK 1.6.0 behaves:
java -Xms2m -Xmx8m GCTest 16 1 > tail_16_01.out
java -Xms2m -Xmx8m GCTest 16 8 > tail_16_08.out
java -Xms2m -Xmx8m GCTest 16 16 > tail_16_16.out
java -Xms2m -Xmx8m GCTest 16 24 > tail_16_24.out
Test "java -Xms2m -Xmx8m GCTest 16 24" gave me an OutOfMemoryError similar to JDK 1.4.0
as shown below:
Time Total Free Free Total Act. Dead Over
sec. Mem. Mem. Per. Obj. Obj. Obj. Head
0 1984 1772 89% 0 0 0 212
0 1984 1643 82% 128 128 0 213
1 1984 1515 76% 256 256 0 213
1 1984 1387 69% 384 384 0 213
2 1984 1259 63% 512 512 0 213
2 1984 1131 57% 640 640 0 213
3 1984 1107 55% 768 640 128 109
3 1984 1098 55% 896 768 128 -10
4 1984 960 48% 896 896 0 128
4 1984 832 41% 1024 1024 0 128
5 1984 704 35% 1152 1152 0 128
5 1984 576 29% 1280 1280 0 128
6 1984 448 22% 1408 1408 0 128
6 3488 1837 52% 1536 1536 0 115
(Continued on next part...)
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