JVM gc只新生代串行GC

原创

mb648972af0d702 2023-06-15 07:02:03 博主文章分类：性能问题 ©著作权

文章标签 full gc 问题 sed java System 文章分类 JavaScript 前端开发

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1.代码一：

1. public class JVMTest {  
2. public static void main(String args[]) throws InterruptedException {  
3. byte [] bytes1 = new byte[1024*1024*2];  
4. byte [] bytes2 = new byte[1024*1024*2];  
5. byte [] bytes3 = new byte[1024*1024*4];  
6. 2000);  
7. byte [] bytes4 = new byte[1024*1024*4];  
8. 2000);  
9.     }  
10. }

执行：java -Xms20M -Xmx20M -Xmn10M -XX:+UseSerialGC -XX:+PrintHeapAtGC -Xloggc:gc.log JVMTest

gc两次：

1. {Heap before GC invocations=0 (full 0):  
2. new generation   total 9216K, used 5287K [7f9a00000, 7fa400000, 7fa400000)  
3. 64% used [7f9a00000, 7f9f29c78, 7fa200000)  
4. 0% used [7fa200000, 7fa200000, 7fa300000)  
5. 0% used [7fa300000, 7fa300000, 7fa400000)  
6.  tenured generation   total 10240K, used 0K [7fa400000, 7fae00000, 7fae00000)  
7. 0% used [7fa400000, 7fa400000, 7fa400200, 7fae00000)  
8. 800000000)  
9. 22% used [7fae00000, 7fb2b3628, 7fb2b3800, 7fc2c0000)  
10. No shared spaces configured.  
11. 0.904: [GC 5287K->4447K(19456K), 0.0315833 secs]  
12. Heap after GC invocations=1 (full 0):  
13. new generation   total 9216K, used 351K [7f9a00000, 7fa400000, 7fa400000)  
14. 0% used [7f9a00000, 7f9a00000, 7fa200000)  
15. 34% used [7fa300000, 7fa357ed8, 7fa400000)  
16. 0% used [7fa200000, 7fa200000, 7fa300000)  
17.  tenured generation   total 10240K, used 4096K [7fa400000, 7fae00000, 7fae00000)  
18. 40% used [7fa400000, 7fa800020, 7fa800200, 7fae00000)  
19. 800000000)  
20. 22% used [7fae00000, 7fb2b3628, 7fb2b3800, 7fc2c0000)  
21. No shared spaces configured.  
22. }  
23. {Heap before GC invocations=1 (full 0):  
24. new generation   total 9216K, used 4711K [7f9a00000, 7fa400000, 7fa400000)  
25. 53% used [7f9a00000, 7f9e41eb0, 7fa200000)  
26. 34% used [7fa300000, 7fa357ed8, 7fa400000)  
27. 0% used [7fa200000, 7fa200000, 7fa300000)  
28.  tenured generation   total 10240K, used 4096K [7fa400000, 7fae00000, 7fae00000)  
29. 40% used [7fa400000, 7fa800020, 7fa800200, 7fae00000)  
30. 800000000)  
31. 22% used [7fae00000, 7fb2b4498, 7fb2b4600, 7fc2c0000)  
32. No shared spaces configured.  
33. 2.940: [GC 8807K->8537K(19456K), 0.0193472 secs]  
34. Heap after GC invocations=2 (full 0):  
35. new generation   total 9216K, used 345K [7f9a00000, 7fa400000, 7fa400000)  
36. 0% used [7f9a00000, 7f9a00000, 7fa200000)  
37. 33% used [7fa200000, 7fa2566e8, 7fa300000)  
38. 0% used [7fa300000, 7fa300000, 7fa400000)  
39.  tenured generation   total 10240K, used 8192K [7fa400000, 7fae00000, 7fae00000)  
40. 80% used [7fa400000, 7fac00030, 7fac00200, 7fae00000)  
41. 800000000)  
42. 22% used [7fae00000, 7fb2b4498, 7fb2b4600, 7fc2c0000)  
43. No shared spaces configured.  
44. }

2.代码2：

1. public class JVMTest {  
2. public static void main(String args[]) throws InterruptedException {  
3. byte [] bytes1 = new byte[1024*1024*2];  
4. byte [] bytes2 = new byte[1024*1024*2];  
5. byte [] bytes3 = new byte[1024*1024*2];  
6. "step 1");  
7. byte [] bytes4 = new byte[1024*1024*2];  
8. 2000);  
9. "step 2");  
10. byte [] bytes5 = new byte[1024*1024*2];  
11. byte [] bytes6 = new byte[1024*1024*2];  
12. "step 3");  
13. byte [] bytes7 = new byte[1024*1024*2];  
14. 2000);  
15.     }  
16. }

java -Xms20M -Xmx20M -Xmn10M -XX:+UseSerialGC -XX:+PrintHeapAtGC -Xloggc:gc.log JVMTest

1次minor gc 一次full gc：原因 minor gc晋升到旧生代的大小大于旧生代的剩余空间。

1. {Heap before GC invocations=0 (full 0):  
2. new generation   total 9216K, used 7335K [7f9a00000, 7fa400000, 7fa400000)  
3. 89% used [7f9a00000, 7fa129c88, 7fa200000)  
4. 0% used [7fa200000, 7fa200000, 7fa300000)  
5. 0% used [7fa300000, 7fa300000, 7fa400000)  
6.  tenured generation   total 10240K, used 0K [7fa400000, 7fae00000, 7fae00000)  
7. 0% used [7fa400000, 7fa400000, 7fa400200, 7fae00000)  
8. 800000000)  
9. 22% used [7fae00000, 7fb2b38c0, 7fb2b3a00, 7fc2c0000)  
10. No shared spaces configured.  
11. 1.019: [GC 7335K->6495K(19456K), 0.0418591 secs]  
12. Heap after GC invocations=1 (full 0):  
13. new generation   total 9216K, used 351K [7f9a00000, 7fa400000, 7fa400000)  
14. 0% used [7f9a00000, 7f9a00000, 7fa200000)  
15. 34% used [7fa300000, 7fa357ed8, 7fa400000)  
16. 0% used [7fa200000, 7fa200000, 7fa300000)  
17.  tenured generation   total 10240K, used 6144K [7fa400000, 7fae00000, 7fae00000)  
18. 60% used [7fa400000, 7faa00030, 7faa00200, 7fae00000)  
19. 800000000)  
20. 22% used [7fae00000, 7fb2b38c0, 7fb2b3a00, 7fc2c0000)  
21. No shared spaces configured.  
22. }  
23. {Heap before GC invocations=1 (full 0):  
24. new generation   total 9216K, used 6754K [7f9a00000, 7fa400000, 7fa400000)  
25. 78% used [7f9a00000, 7fa040af0, 7fa200000)  
26. 34% used [7fa300000, 7fa357ed8, 7fa400000)  
27. 0% used [7fa200000, 7fa200000, 7fa300000)  
28.  tenured generation   total 10240K, used 6144K [7fa400000, 7fae00000, 7fae00000)  
29. 60% used [7fa400000, 7faa00030, 7faa00200, 7fae00000)  
30. 800000000)  
31. 22% used [7fae00000, 7fb2b47b0, 7fb2b4800, 7fc2c0000)  
32. No shared spaces configured.  
33. 3.073: [Full GC 12898K->12633K(19456K), 0.0712905 secs]  
34. Heap after GC invocations=2 (full 1):  
35. new generation   total 9216K, used 4441K [7f9a00000, 7fa400000, 7fa400000)  
36. 54% used [7f9a00000, 7f9e56680, 7fa200000)  
37. 0% used [7fa300000, 7fa300000, 7fa400000)  
38. 0% used [7fa200000, 7fa200000, 7fa300000)  
39.  tenured generation   total 10240K, used 8192K [7fa400000, 7fae00000, 7fae00000)  
40. 80% used [7fa400000, 7fac000c8, 7fac00200, 7fae00000)  
41. 800000000)  
42. 22% used [7fae00000, 7fb2b47b0, 7fb2b4800, 7fc2c0000)  
43. No shared spaces configured.  
44. }

新生代对象晋升到旧生代的规则：经过多次minor gc之后还存在的对象或者是to space放不下的直接晋升到old generation