我正在尝试调整G1 GC。应用程序运行有时然后堆已满，但它显示Eden，survivor和old的区域为0并且调用完整的GC以释放空间。
我使用过的旗帜： Xmx：30G -XX：+ UseG1GC -XX：+ AlwaysPreTouch -XX：+ UseStringDeduplication -XX：+ UseCompressedClassPointers -XX：+ UseCompressedOops -XX：+ ExplicitGCInvokesConcurrent -XX：+ ParallelRefProcEnabled -XX：MaxGCPauseMillis = 200 -XX：ParallelGCThreads = 12 -XX：ConcGCThreads = 4
GC日志：
{Heap before GC invocations=629 (full 0):
garbage-first heap total 31457280K, used 31434556K [0x0000000080000000, 0x0000000080807800, 0x0000000800000000)
region size 8192K, 0 young (0K), 0 survivors (0K)
Metaspace used 41962K, capacity 42424K, committed 42956K, reserved 1087488K
class space used 4589K, capacity 4749K, committed 4812K, reserved 1048576K
2017-12-07T14:47:41.979+0000: [GC pause (G1 Evacuation Pause) (young)
Desired survivor size 100663296 bytes, new threshold 15 (max 15)
18116.906: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 0, predicted base time: 48.13 ms, remaining time: 151.87 ms, target pause time: 200.00 ms]
18116.906: [G1Ergonomics (CSet Construction) add young regions to CSet, eden: 0 regions, survivors: 0 regions, predicted young region time: 0.00 ms]
18116.906: [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 0 regions, survivors: 0 regions, old: 0 regions, predicted pause time: 48.13 ms, target pause time: 200.00 ms]
2017-12-07T14:47:41.981+0000: [SoftReference, 0 refs, 0.0004177 secs]2017-12-07T14:47:41.981+0000: [WeakReference, 0 refs, 0.0002174 secs]2017-12-07T14:47:41.981+0000: [FinalReference, 0 refs, 0.0003298 secs]2017-12-07T14:47:41.982+0000: [PhantomReference, 0 refs, 0 refs, 0.0004635 secs]2017-12-07T14:47:41.982+0000: [JNI Weak Reference, 0.0000152 secs], 0.0439856 secs]
[Parallel Time: 1.4 ms, GC Workers: 12]
[GC Worker Start (ms): Min: 18116906.3, Avg: 18116906.3, Max: 18116906.4, Diff: 0.1]
[Ext Root Scanning (ms): Min: 0.5, Avg: 0.6, Max: 0.9, Diff: 0.4, Sum: 6.9]
[Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[Processed Buffers: Min: 0, Avg: 0.1, Max: 1, Diff: 1, Sum: 1]
[Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Object Copy (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.4]
[Termination (ms): Min: 0.0, Avg: 0.6, Max: 0.7, Diff: 0.7, Sum: 6.8]
[Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 12]
[GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[GC Worker Total (ms): Min: 1.2, Avg: 1.2, Max: 1.3, Diff: 0.1, Sum: 15.0]
[GC Worker End (ms): Min: 18116907.6, Avg: 18116907.6, Max: 18116907.6, Diff: 0.0]
[Code Root Fixup: 0.1 ms]
[Code Root Purge: 0.0 ms]
[String Dedup Fixup: 39.9 ms, GC Workers: 12]
[Queue Fixup (ms): Min: 0.0, Avg: 11.3, Max: 18.1, Diff: 18.1, Sum: 135.1]
[Table Fixup (ms): Min: 21.7, Avg: 27.8, Max: 35.2, Diff: 13.5, Sum: 333.3]
[Clear CT: 0.1 ms]
[Other: 2.5 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 1.6 ms]
[Ref Enq: 0.1 ms]
[Redirty Cards: 0.1 ms]
[Humongous Register: 0.2 ms]
[Humongous Reclaim: 0.0 ms]
[Free CSet: 0.1 ms]
[Eden: 0.0B(1536.0M)->0.0B(1536.0M) Survivors: 0.0B->0.0B Heap: 30.0G(30.0G)->30.0G(30.0G)]
Heap after GC invocations=630 (full 0):
garbage-first heap total 31457280K, used 31434556K [0x0000000080000000, 0x0000000080807800, 0x0000000800000000)
region size 8192K, 0 young (0K), 0 survivors (0K)
Metaspace used 41962K, capacity 42424K, committed 42956K, reserved 1087488K
class space used 4589K, capacity 4749K, committed 4812K, reserved 1048576K
}
[Times: user=0.49 sys=0.01, real=0.05 secs]
{Heap before GC invocations=630 (full 0):
garbage-first heap total 31457280K, used 31434556K [0x0000000080000000, 0x0000000080807800, 0x0000000800000000)
region size 8192K, 0 young (0K), 0 survivors (0K)
Metaspace used 41962K, capacity 42424K, committed 42956K, reserved 1087488K
class space used 4589K, capacity 4749K, committed 4812K, reserved 1048576K
2017-12-07T14:47:42.024+0000: [GC pause (G1 Evacuation Pause) (young)
Desired survivor size 100663296 bytes, new threshold 15 (max 15)
18116.952: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 0, predicted base time: 47.06 ms, remaining time: 152.94 ms, target pause time: 200.00 ms]
18116.952: [G1Ergonomics (CSet Construction) add young regions to CSet, eden: 0 regions, survivors: 0 regions, predicted young region time: 0.00 ms]
18116.952: [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 0 regions, survivors: 0 regions, old: 0 regions, predicted pause time: 47.06 ms, target pause time: 200.00 ms]
2017-12-07T14:47:42.026+0000: [SoftReference, 0 refs, 0.0003988 secs]2017-12-07T14:47:42.027+0000: [WeakReference, 0 refs, 0.0003844 secs]2017-12-07T14:47:42.027+0000: [FinalReference, 0 refs, 0.0002286 secs]2017-12-07T14:47:42.027+0000: [PhantomReference, 0 refs, 0 refs, 0.0004361 secs]2017-12-07T14:47:42.028+0000: [JNI Weak Reference, 0.0000169 secs], 0.0433898 secs]
[Parallel Time: 1.5 ms, GC Workers: 12]
[GC Worker Start (ms): Min: 18116952.0, Avg: 18116952.1, Max: 18116952.1, Diff: 0.1]
[Ext Root Scanning (ms): Min: 0.7, Avg: 0.8, Max: 0.9, Diff: 0.1, Sum: 9.5]
[Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.2, Diff: 0.2, Sum: 0.2]
[Processed Buffers: Min: 0, Avg: 0.1, Max: 1, Diff: 1, Sum: 1]
[Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Object Copy (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.5]
[Termination (ms): Min: 0.0, Avg: 0.4, Max: 0.5, Diff: 0.5, Sum: 5.3]
[Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 12]
[GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[GC Worker Total (ms): Min: 1.3, Avg: 1.3, Max: 1.4, Diff: 0.1, Sum: 16.1]
[GC Worker End (ms): Min: 18116953.4, Avg: 18116953.4, Max: 18116953.4, Diff: 0.0]
[Code Root Fixup: 0.1 ms]
[Code Root Purge: 0.0 ms]
[String Dedup Fixup: 39.2 ms, GC Workers: 12]
[Queue Fixup (ms): Min: 0.0, Avg: 11.4, Max: 15.4, Diff: 15.4, Sum: 136.9]
[Table Fixup (ms): Min: 23.7, Avg: 27.7, Max: 39.1, Diff: 15.4, Sum: 332.3]
[Clear CT: 0.1 ms]
[Other: 2.5 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 1.6 ms]
[Ref Enq: 0.1 ms]
[Redirty Cards: 0.1 ms]
[Humongous Register: 0.2 ms]
[Humongous Reclaim: 0.0 ms]
[Free CSet: 0.1 ms]
[Eden: 0.0B(1536.0M)->0.0B(1536.0M) Survivors: 0.0B->0.0B Heap: 30.0G(30.0G)->30.0G(30.0G)]
Heap after GC invocations=631 (full 0):
garbage-first heap total 31457280K, used 31434556K [0x0000000080000000, 0x0000000080807800, 0x0000000800000000)
region size 8192K, 0 young (0K), 0 survivors (0K)
Metaspace used 41962K, capacity 42424K, committed 42956K, reserved 1087488K
class space used 4589K, capacity 4749K, committed 4812K, reserved 1048576K
}
[Times: user=0.49 sys=0.00, real=0.04 secs]
18116.996: [G1Ergonomics (Heap Sizing) attempt heap expansion, reason: allocation request failed, allocation request: 16 bytes]
18116.997: [G1Ergonomics (Heap Sizing) expand the heap, requested expansion amount: 8388608 bytes, attempted expansion amount: 8388608 bytes]
18116.997: [G1Ergonomics (Heap Sizing) did not expand the heap, reason: heap already fully expanded]
{Heap before GC invocations=631 (full 0):
garbage-first heap total 31457280K, used 31434556K [0x0000000080000000, 0x0000000080807800, 0x0000000800000000)
region size 8192K, 0 young (0K), 0 survivors (0K)
Metaspace used 41962K, capacity 42424K, committed 42956K, reserved 1087488K
class space used 4589K, capacity 4749K, committed 4812K, reserved 1048576K
2017-12-07T14:47:42.069+0000: [Full GC (Allocation Failure) 2017-12-07T14:48:06.386+0000: [SoftReference, 122 refs, 0.0001069 secs]2017-12-07T14:48:06.386+0000: [WeakReference, 22631 refs, 0.0079235 secs]2017-12-07T14:48:06.394+0000: [FinalReference, 395 refs, 0.0005771 secs]2017-12-07T14:48:06.394+0000: [PhantomReference, 0 refs, 0 refs, 0.0000163 secs]2017-12-07T14:48:06.394+0000: [JNI Weak Reference, 0.0000357 secs] 29G->14G(30G), 53.8180666 secs]
[Eden: 0.0B(1536.0M)->0.0B(1536.0M) Survivors: 0.0B->0.0B Heap: 30.0G(30.0G)->14.4G(30.0G)], [Metaspace: 41962K->41951K(1087488K)]
Heap after GC invocations=632 (full 1):
garbage-first heap total 31457280K, used 15144510K [0x0000000080000000, 0x0000000080807800, 0x0000000800000000)
region size 8192K, 0 young (0K), 0 survivors (0K)
Metaspace used 41951K, capacity 42406K, committed 42956K, reserved 1087488K
class space used 4587K, capacity 4746K, committed 4812K, reserved 1048576K
}
请帮我弄清楚问题以及如何避免使用完整的GC。
答案 0 :(得分：1)
这可能是OpenJDK bug 8165150，这意味着您在Full GC之前遇到了noop young gen集合。这不是最理想的，但只要完整的GC发生并且可以释放内存，JVM就应该恢复。
您可以通过确保堆中有足够的可用空间，应用程序不会泄漏以及在填满之前启动并发周期来避免此问题，例如：通过调整IHOP。
Full GC后的生活设定大小仅为14GiB，因此IHOP约为60％可能会有所帮助。
答案 1 :(得分：-2)
您还可以通过编写如下代码来手动重置变量：
variable = null
如果你的变量中存有大对象，这很有用。