为什么JVM不能将堆内存自动扩展到linux&;中配置的Xmx3072m;jdk1.6.0_32和FullGC经常出现
为什么在linux和jdk1.6.0_32中JVM内存不能自动扩展到Xmx3072m 终身使用的一代使用率为99%,并且借给FullGC的频率非常高。java进程只使用1G内存,这可以从为什么JVM不能将堆内存自动扩展到linux&;中配置的Xmx3072m;jdk1.6.0_32和FullGC经常出现,linux,garbage-collection,jvm,Linux,Garbage Collection,Jvm,为什么在linux和jdk1.6.0_32中JVM内存不能自动扩展到Xmx3072m 终身使用的一代使用率为99%,并且借给FullGC的频率非常高。java进程只使用1G内存,这可以从top的输出中看出 如果我们将JVM参数更改为-Xms3072m-Xmx3072m,那么它可以正常工作。但是如果我们使用-Xms256m-Xmx3072m,那么问题就会出现,并且FullGC经常发生 这两个参数也是默认值: MinHeapFreeRatio 40 MaxHeapFreeRatio 70
top
的输出中看出
如果我们将JVM参数更改为-Xms3072m-Xmx3072m
,那么它可以正常工作。但是如果我们使用-Xms256m-Xmx3072m
,那么问题就会出现,并且FullGC经常发生
这两个参数也是默认值:
MinHeapFreeRatio 40
MaxHeapFreeRatio 70
环境是:
OS:
Linux linux-wgvb 2.6.16.60-0.54.5-smp #1 SMP Fri Sep 4 01:28:03 UTC 2009 x86_64 x86_64 x86_64 GNU/Linux
JDK version:
java version "1.6.0_32"
Java(TM) SE Runtime Environment (build 1.6.0_32-b05)
Java HotSpot(TM) 64-Bit Server VM (build 20.7-b02, mixed mode)
JVM params:
-Xms256m -Xmx3072m -XX:+UseParallelOldGC -XX:MaxGCPauseMillis=1000
-XX:ParallelGCThreads=5 -Xrs -XX:PermSize=64m -XX:MaxPermSize=512m
-XX:+HeapDumpOnOutOfMemoryError
FullGC经常执行:
@linux> ./jstat -gcutil 18261 1000 500
S0 S1 E O P YGC YGCT FGC FGCT GCT
0.00 64.67 7.04 99.53 71.89 18293 510.574 1167 1616.594 2127.168
91.78 7.91 100.00 99.53 72.00 18299 510.821 1167 1616.594 2127.415
77.49 0.00 0.00 99.99 72.00 18300 510.947 1168 1616.594 2127.541
0.00 99.83 25.71 99.49 71.72 18305 511.178 1168 1617.915 2129.093
24.27 0.00 21.74 99.67 71.73 18310 511.342 1168 1617.915 2129.256
28.57 0.00 0.00 99.83 71.73 18314 511.427 1169 1617.915 2129.342
0.00 29.29 0.00 99.56 71.82 18317 511.465 1169 1618.919 2130.384
0.00 78.85 54.96 99.56 72.05 18326 511.777 1169 1618.919 2130.696
64.52 0.00 0.00 99.99 72.05 18328 511.920 1170 1618.919 2130.839
0.00 99.26 0.00 99.88 71.71 18333 512.079 1171 1620.014 2132.093
4.86 0.00 0.00 99.95 71.76 18338 512.255 1172 1620.957 2133.211
80.98 0.00 0.00 99.69 71.83 18350 512.453 1172 1621.906 2134.359
0.00 64.48 0.00 99.85 71.83 18355 512.677 1173 1621.906 2134.583
0.00 99.80 0.00 99.93 71.71 18359 512.876 1174 1623.264 2136.139
0.06 0.04 100.00 99.55 71.71 18360 512.876 1174 1624.193 2137.069
60.35 0.00 0.00 99.90 71.77 18376 513.429 1175 1624.193 2137.622
60.35 0.00 0.00 99.90 71.77 18376 513.429 1175 1624.193 2137.622
89.86 0.00 0.00 99.83 71.78 18384 513.839 1176 1625.476 2139.315
89.86 0.00 0.00 99.83 71.78 18384 513.839 1176 1625.476 2139.315
0.00 39.17 64.41 99.60 71.78 18394 514.202 1176 1626.880 2141.082
99.93 0.00 0.00 99.82 71.78 18396 514.326 1177 1626.880 2141.206
0.00 64.68 0.00 99.61 71.72 18401 514.409 1177 1627.945 2142.354
java进程仅使用1G内存:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
18261 ouser 15 0 4353m 1.0g 52m S 325 3.2 271:25.52 java
/jstat-总容量18261 1000 500
NGCMN NGCMX NGC S0C S1C EC OGCMN OGCMX OGC OC PGCMN PGCMX PGC PC YGC FGC 87360.0 1048576.0 136256.0 65984.0 68096.0 64.0 174784.0 2097152.0 785664.0 785664.0 65536.0 524288.0 65792.0 65792.0 141612 8100 87360.0 1048576.0 122816.0 61376.0 12992.0 64.0 174784.0 2097152.0 791360.0 791360.0 65536.0 524288.0 65792.0 65792.0 141616 8100 87360.0 1048576.0 115264.0 57600.0 7872.0 64.0 174784.0 2097152.0 791936.0 791936.0 65536.0 524288.0 65792.0 65792.0 141617 8101
87360.0 1048576.0 112576.0 54912.0 56256.0 64.0 174784.0 2097152.0 797952.0 797952.0 65536.0 524288.0 65792.0 65792.0 141618 8102
87360.0 1048576.0 112576.0 54912.0 56256.0 64.0 174784.0 2097152.0 797952.0 797952.0 65536.0 524288.0 65792.0 65792.0 141618 8102 87360.0 1048576.0 105408.0 52672.0 192.0 64.0 174784.0 2097152.0 804096.0 804096.0 65536.0 524288.0 65792.0 65792.0 141621 8103 87360.0 1048576.0 87360.0 35584.0 38464.0 8064.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141629 8103 87360.0 1048576.0 111168.0 39488.0 46080.0 12416.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141635 8103 87360.0 1048576.0 142848.0 69440.0 70592.0 1664.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141644 8104 87360.0 1048576.0 142848.0 69440.0 70592.0 1664.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141644 8104 87360.0 1048576.0 87360.0 35136.0 37376.0 10304.0 174784.0 2097152.0 769280.0 769280.0 65536.0 524288.0 65792.0 65792.0 141661 8105
RES
值不是进程使用了多少内存,而是进程实际使用了多少RAM。这不包括交换的页面和已分配但未映射的页面。确保系统本身有足够的可用内存,您可以运行free
,甚至top
应该打印超过使用的内存量。top
的输出表明进程映射了4G内存,但当前未在RAM中(即VIRT
值)。我认为JVM命令行选项是正确的。也许您监控JVN堆的方法是错误的
VIRT
是进度要求的全部空间,如果空间不够,可能会使用swap
也许您可以使用jstat-gccapacity 18261 1000 500
查看各代及其相应空间的容量统计信息
gc Garbage-collected heap statistics
+-------+-------------------------------------------+
|Column | Description |
+-------+-------------------------------------------+
|SOC | Current survivor space 0 capacity (KB). |
|S1C | Current survivor space 1 capacity (KB). |
|S0U | Survivor space 0 utilization (KB). |
|S1U | Survivor space 1 utilization (KB). |
|EC | Current eden space capacity (KB). |
|EU | Eden space utilization (KB). |
|OC | Current old space capacity (KB). |
|OU | Old space utilization (KB). |
|PC | Current permanent space capacity (KB). |
|PU | Permanent space utilization (KB). |
|YGC | Number of young generation GC Events. |
|YGCT | Young generation garbage collection time. |
|FGC | Number of full GC events. |
|FGCT | Full garbage collection time. |
|GCT | Total garbage collection time. |
+-------+-------------------------------------------+
您能检查您的
-XX:+UseAptiveSizePolicy
是否已设置?默认情况下,它应该处于启用状态
此外,您可能会给它太小的Xms
,因此GC无法在如此短的时间内恢复堆区域并调整其大小。您可以试试例如-Xms1024m-Xmx3072m
和-Xms2048m-Xmx3072m
?在这些情况下,GC是否能够适当调整尺寸?(实时监控jstat-gccapacity
可能会有所帮助。)
一般来说,useAptiveSizePolicy
是有用的,并且该算法能够调整堆的人体工程学。但是,主要的责任始终在于用户观察应用程序的内存分配行为,并根据自己的最佳利益设置GC参数。很可能是-Xms256m-Xmx3072m
根本不足以跟上您的分配率和实时数据集的大小
顺便说一句,我认为系统内存没有问题,因为当您从一开始就给GC足够的内存时(例如,
-Xms3072m-Xmx3072m
),GC表现良好。但是为什么如果我们将JVM参数更改为-Xms3072m-Xmx3072m,那么它工作正常呢。如果我们使用-Xms256m-Xmx3072m,那么问题就会出现,而且FullGC发生得非常频繁?是否有可用的RAM?JVM不会尝试使用不可用的内存,除非您强制使用,因为您将进入交换抖动,在大多数情况下,它的性能比GC差。@linux wgvb:/opt/jdk/jdk1.6.0_32/bin>缓存的空闲共享缓冲区的空闲总使用量Mem:32937336 2885076 40867600 259204 18551848-/+buffers/cache:10039524 22897812
交换:2104472 328762071596@linux-wgvb:/opt/jdk/jdk1.6.0_32/bin>top-top-top-14:32:06最多8天,22:23,7个用户,平均负载:12.30,15.25,16.44任务:总共344个,1个运行,343个睡眠,0个停止,0个僵尸Cpu:35.3%美国,4.9%sy,0.0%ni,56.7%id,3.0%wa,0.0%hi,0.1%si,0.0%st Mem:32165M总数,28204M使用,3960M空闲,253M缓冲区交换:总共2055M,使用32M,2023M空闲,18117M缓存,所以您确实有22G空闲(18个带有可丢弃缓存数据)@linux wgvb:/opt/jdk/jdk1.6.0_32/bin>/jstat-gccapacity 18261 1000 500 NGCMN NGCMX NGC S0C S1C EC OGCMN OGCMX OGC OC PGCMN PGCMX PGC PC YGC FGC 87360.0 1048576.0 87360.0 34688.0 32896.0 19776.0 174784.0 2097152.0 599104.0 599104.0 65536.0 524288.0 65792.0六万五千七百九十二点零一三二五七六
gc Garbage-collected heap statistics
+-------+-------------------------------------------+
|Column | Description |
+-------+-------------------------------------------+
|SOC | Current survivor space 0 capacity (KB). |
|S1C | Current survivor space 1 capacity (KB). |
|S0U | Survivor space 0 utilization (KB). |
|S1U | Survivor space 1 utilization (KB). |
|EC | Current eden space capacity (KB). |
|EU | Eden space utilization (KB). |
|OC | Current old space capacity (KB). |
|OU | Old space utilization (KB). |
|PC | Current permanent space capacity (KB). |
|PU | Permanent space utilization (KB). |
|YGC | Number of young generation GC Events. |
|YGCT | Young generation garbage collection time. |
|FGC | Number of full GC events. |
|FGCT | Full garbage collection time. |
|GCT | Total garbage collection time. |
+-------+-------------------------------------------+