这是输出jmap -heap
命令:
Survivor Space:
regions = 52
capacity = 54525952 (52.0MB)
used = 54525952 (52.0MB)
free = 0 (0.0MB)
100.0% used
我已经执行了很多次,我发现它的价值capacity
总是等于used
.
我的问题是为什么幸存者空间总是满的(而且很小)?我已指定-Xmx2200m -Xms2200m -Xmn1100m
。
(我预计survivor空间应该是220M,这意味着survivor区域应该有更多的空间)
- 更新 -
jheap 的完整输出:
Garbage-First (G1) GC with 2 thread(s)
Heap Configuration:
MinHeapFreeRatio = 40
MaxHeapFreeRatio = 70
MaxHeapSize = 2306867200 (2200.0MB)
NewSize = 1153433600 (1100.0MB)
MaxNewSize = 1153433600 (1100.0MB)
OldSize = 4194304 (4.0MB)
NewRatio = 2
SurvivorRatio = 8
MetaspaceSize = 16777216 (16.0MB)
CompressedClassSpaceSize = 1073741824 (1024.0MB)
MaxMetaspaceSize = 4294963200 (4095.99609375MB)
G1HeapRegionSize = 1048576 (1.0MB)
Heap Usage:
G1 Heap:
regions = 14488
capacity = 15191769088 (14488.0MB)
used = 1083703304 (1033.5000076293945MB)
free = 14108065784 (13454.499992370605MB)
7.13348983730946% used
G1 Young Generation:
Eden Space:
regions = 988
capacity = 1163919360 (1110.0MB)
used = 1035993088 (988.0MB)
free = 127926272 (122.0MB)
89.009009009009% used
Survivor Space:
regions = 45
capacity = 47185920 (45.0MB)
used = 47185920 (45.0MB)
free = 0 (0.0MB)
100.0% used
G1 Old Generation:
regions = 2
capacity = 1095761920 (1045.0MB)
used = 524296 (0.5000076293945312MB)
free = 1095237624 (1044.4999923706055MB)
0.04784762003775419% used
30424 interned Strings occupying 3027304 bytes.
我的观察。
-
当您停止自定义某些参数时,G1GC 是高效的。我建议删除Xmn
(年轻一代)设置。
-
设置不同的值-Xms
and -Xmx
-
区域大小应配置为最大堆内存大小/2048。对于 4G 堆,区域大小应为 2 MB;对于 2 GB 堆,理想区域大小应为 1 MB。
-
需要配置的关键参数:-XX:G1HeapRegionSize=n, XX:MaxGCPauseMillis=m, -XX:ParallelGCThreads=n, -XX:ConcGCThreads=n
除了-Xms and -Xmx
看看这个SE post https://stackoverflow.com/questions/574021/reducing-jvm-pause-time-1-second-using-useconcmarksweepgc/34186346#34186346 and 信息Q文章 http://www.infoq.com/articles/tuning-tips-G1-GC更多细节。
推荐来自Oracle http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html
当您评估和微调 G1 GC 时,请记住以下建议:
年轻代大小:避免使用 -Xmn 选项或任何或其他相关选项(例如 -XX:NewRatio)显式设置年轻代大小。固定年轻代的大小会覆盖目标暂停时间目标。
暂停时间目标:当您评估或调整任何垃圾收集时,总是存在延迟与吞吐量的权衡。
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