1.昨天中午服務器監(jiān)控提示：服務器xx.xx.xx.xx機器cpu使用率連續(xù)36次超過20%
2.服務器基礎信息：javaweb項目，提供查詢，導出等功能。
3.監(jiān)控信息如下：
yonggc監(jiān)控：
堆內(nèi)存監(jiān)控：
cpu監(jiān)控：
full-gc監(jiān)控：
機器運行實例監(jiān)控
當時機器的gclog：
以上是監(jiān)控信息~
由于其他同事在14：32時手動執(zhí)行了一次fullgc導致，內(nèi)存的一回收，才恢復平靜。
當時，啟動參數(shù)：-Xms4g -Xmx4g -XX:PermSize=300m -XX:MaxPermSize=300m -XX:NewSize=2g -XX:MaxNewSize=2g -XX:SurvivorRatio=20 -XX:MaxTenuringThreshold=10 -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:ParallelGCThreads=4 -XX:+CMSScavengeBeforeRemark -XX:+CMSParallelRemarkEnabled -XX:+ScavengeBeforeFullGC -XX:+UseCMSCompactAtFullCollection -XX:CMSInitiatingPermOccupancyFraction=70 -XX:+ExplicitGCInvokesConcurrent -XX:CMSFullGCsBeforeCompaction=5 -XX:+CMSClassUnloadingEnabled -XX:+UseCMSInitiatingOccupancyOnly -XX:CMSInitiatingOccupancyFraction=30 -Xloggc:/tomcat7-gc-cms.log -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintHeapAtGC -XX:+PrintReferenceGC -XX:+PrintTenuringDistribution
通過查看tomcat7-gc-cms.log分析過程：
14：23有一次fullgc log位置：
fullgc--start
2018-04-16T14:23:45.747+0800: 356595.145: [CMS-concurrent-mark: 1.508/1.538 secs] [Times: user=12.08 sys=0.00, real=1.54 secs]
2018-04-16T14:23:45.748+0800: 356595.145: [CMS-concurrent-preclean-start]
2018-04-16T14:23:45.748+0800: 356595.145: [Preclean SoftReferences, 0.0005960 secs]2018-04-16T14:23:45.748+0800: 356595.145: [Preclean WeakReferences, 0.0001810 secs]2018-04-16T14:23:45.748+0800: 356595.146: [Preclean FinalReferences, 0.0000650 secs]2018-04-16T14:23:45.748+0800: 356595.146: [Preclean PhantomReferences, 0.0000160 secs]2018-04-16T14:23:45.756+0800: 356595.153: [CMS-concurrent-preclean: 0.008/0.009 secs] [Times: user=0.07 sys=0.00, real=0.01 secs]
2018-04-16T14:23:45.756+0800: 356595.154: [CMS-concurrent-abortable-preclean-start]
{Heap before GC invocations=652 (full 1):
par new generation total 2001856K, used 1915155K [0x00000006ed400000, 0x000000076d400000, 0x000000076d400000)
eden space 1906560K, 100% used [0x00000006ed400000, 0x00000007619e0000, 0x00000007619e0000)
from space 95296K, 9% used [0x00000007619e0000, 0x0000000762244da8, 0x00000007676f0000)
to space 95296K, 0% used [0x00000007676f0000, 0x00000007676f0000, 0x000000076d400000)
concurrent mark-sweep generation total 2097152K, used 629223K [0x000000076d400000, 0x00000007ed400000, 0x00000007ed400000)
concurrent-mark-sweep perm gen total 307200K, used 143890K [0x00000007ed400000, 0x0000000800000000, 0x0000000800000000)
2018-04-16T14:23:45.976+0800: 356595.373: [GC2018-04-16T14:23:45.976+0800: 356595.373: [ParNew2018-04-16T14:23:45.988+0800: 356595.385: [SoftReference, 0 refs, 0.0000510 secs]2018-04-16T14:23:45.988+0800: 356595.385: [WeakReference, 25 refs, 0.0000140 secs]2018-04-16T14:23:45.988+0800: 356595.385: [FinalReference, 45 refs, 0.0000290 secs]2018-04-16T14:23:45.988+0800: 356595.385: [PhantomReference, 0 refs, 0.0000100 secs]2018-04-16T14:23:45.988+0800: 356595.385: [JNI Weak Reference, 0.0000100 secs]
Desired survivor size 48791552 bytes, new threshold 10 (max 10)
- age 1: 3537312 bytes, 3537312 total
- age 2: 1668536 bytes, 5205848 total
- age 3: 337152 bytes, 5543000 total
- age 4: 14496 bytes, 5557496 total
- age 5: 16456 bytes, 5573952 total
- age 6: 10904 bytes, 5584856 total
- age 7: 12664 bytes, 5597520 total
- age 8: 14056 bytes, 5611576 total
- age 9: 11808 bytes, 5623384 total
- age 10: 18184 bytes, 5641568 total
: 1915155K->8115K(2001856K), 0.0122020 secs] 2544378K->637347K(4099008K), 0.0124670 secs] [Times: user=0.04 sys=0.00, real=0.01 secs]
Heap after GC invocations=653 (full 1):
par new generation total 2001856K, used 8115K [0x00000006ed400000, 0x000000076d400000, 0x000000076d400000)
eden space 1906560K, 0% used [0x00000006ed400000, 0x00000006ed400000, 0x00000007619e0000)
from space 95296K, 8% used [0x00000007676f0000, 0x0000000767edcca0, 0x000000076d400000)
to space 95296K, 0% used [0x00000007619e0000, 0x00000007619e0000, 0x00000007676f0000)
concurrent mark-sweep generation total 2097152K, used 629232K [0x000000076d400000, 0x00000007ed400000, 0x00000007ed400000)
concurrent-mark-sweep perm gen total 307200K, used 143890K [0x00000007ed400000, 0x0000000800000000, 0x0000000800000000)
}
2018-04-16T14:23:46.346+0800: 356595.743: [CMS-concurrent-abortable-preclean: 0.274/0.590 secs] [Times: user=4.61 sys=0.00, real=0.59 secs]
2018-04-16T14:23:46.351+0800: 356595.748: [GC[YG occupancy: 1249269 K (2001856 K)]{Heap before GC invocations=653 (full 1):
par new generation total 2001856K, used 1249269K [0x00000006ed400000, 0x000000076d400000, 0x000000076d400000)
eden space 1906560K, 65% used [0x00000006ed400000, 0x00000007390109d8, 0x00000007619e0000)
from space 95296K, 8% used [0x00000007676f0000, 0x0000000767edcca0, 0x000000076d400000)
to space 95296K, 0% used [0x00000007619e0000, 0x00000007619e0000, 0x00000007676f0000)
concurrent mark-sweep generation total 2097152K, used 629232K [0x000000076d400000, 0x00000007ed400000, 0x00000007ed400000)
concurrent-mark-sweep perm gen total 307200K, used 143890K [0x00000007ed400000, 0x0000000800000000, 0x0000000800000000)
2018-04-16T14:23:46.351+0800: 356595.748: [GC2018-04-16T14:23:46.351+0800: 356595.748: [ParNew2018-04-16T14:23:46.363+0800: 356595.760: [SoftReference, 0 refs, 0.0000360 secs]2018-04-16T14:23:46.363+0800: 356595.760: [WeakReference, 24 refs, 0.0000140 secs]2018-04-16T14:23:46.363+0800: 356595.760: [FinalReference, 48 refs, 0.0000200 secs]2018-04-16T14:23:46.363+0800: 356595.760: [PhantomReference, 0 refs, 0.0000100 secs]2018-04-16T14:23:46.363+0800: 356595.760: [JNI Weak Reference, 0.0000090 secs]
Desired survivor size 48791552 bytes, new threshold 10 (max 10)
- age 1: 2807512 bytes, 2807512 total
- age 2: 1240272 bytes, 4047784 total
- age 3: 487568 bytes, 4535352 total
- age 4: 86712 bytes, 4622064 total
- age 5: 8384 bytes, 4630448 total
- age 6: 12944 bytes, 4643392 total
- age 7: 9152 bytes, 4652544 total
- age 8: 10872 bytes, 4663416 total
- age 9: 11560 bytes, 4674976 total
- age 10: 8456 bytes, 4683432 total
: 1249269K->5485K(2001856K), 0.0116790 secs] 1878501K->634726K(4099008K), 0.0119130 secs] [Times: user=0.04 sys=0.00, real=0.02 secs]
Heap after GC invocations=654 (full 1):
par new generation total 2001856K, used 5485K [0x00000006ed400000, 0x000000076d400000, 0x000000076d400000)
eden space 1906560K, 0% used [0x00000006ed400000, 0x00000006ed400000, 0x00000007619e0000)
from space 95296K, 5% used [0x00000007619e0000, 0x0000000761f3b450, 0x00000007676f0000)
to space 95296K, 0% used [0x00000007676f0000, 0x00000007676f0000, 0x000000076d400000)
concurrent mark-sweep generation total 2097152K, used 629241K [0x000000076d400000, 0x00000007ed400000, 0x00000007ed400000)
concurrent-mark-sweep perm gen total 307200K, used 143890K [0x00000007ed400000, 0x0000000800000000, 0x0000000800000000)
}
2018-04-16T14:23:46.363+0800: 356595.760: [Rescan (parallel) , 0.0037940 secs]2018-04-16T14:23:46.367+0800: 356595.764: [weak refs processing2018-04-16T14:23:46.367+0800: 356595.764: [SoftReference, 14978 refs, 0.0015960 secs]2018-04-16T14:23:46.368+0800: 356595.766: [WeakReference, 449 refs, 0.0000620 secs]2018-04-16T14:23:46.369+0800: 356595.766: [FinalReference, 1472 refs, 0.0051820 secs]2018-04-16T14:23:46.374+0800: 356595.771: [PhantomReference, 1 refs, 0.0000130 secs]2018-04-16T14:23:46.374+0800: 356595.771: [JNI Weak Reference, 0.0000100 secs], 0.0069140 secs]2018-04-16T14:23:46.374+0800: 356595.771: [class unloading, 0.0269340 secs]2018-04-16T14:23:46.401+0800: 356595.798: [scrub symbol table, 0.0164990 secs]2018-04-16T14:23:46.417+0800: 356595.815: [scrub string table, 0.0036960 secs] [1 CMS-remark: 629241K(2097152K)] 634726K(4099008K), 0.0799200 secs] [Times: user=0.12 sys=0.00, real=0.08 secs]
2018-04-16T14:23:46.431+0800: 356595.828: [CMS-concurrent-sweep-start]
2018-04-16T14:23:46.802+0800: 356596.199: [CMS-concurrent-sweep: 0.363/0.371 secs] [Times: user=2.89 sys=0.00, real=0.37 secs]
2018-04-16T14:23:46.802+0800: 356596.199: [CMS-concurrent-reset-start]
2018-04-16T14:23:46.835+0800: 356596.233: [CMS-concurrent-reset: 0.033/0.033 secs] [Times: user=0.27 sys=0.00, real=0.04 secs]
**fullgc-end**
通過fullgc后的一次yonggc分析發(fā)現(xiàn)：
{Heap before GC invocations=654 (full 1):
par new generation total 2001856K, used 1912541K [0x00000006ed400000, 0x000000076d400000, 0x000000076d400000)
eden space 1906560K, 100% used [0x00000006ed400000, 0x00000007619e0000, 0x00000007619e0000)
from space 95296K, 6% used [0x00000007619e0000, 0x0000000761fb7548, 0x00000007676f0000)
to space 95296K, 0% used [0x00000007676f0000, 0x00000007676f0000, 0x000000076d400000)
concurrent mark-sweep generation total 2097152K, used 259145K [0x000000076d400000, 0x00000007ed400000, 0x00000007ed400000)
concurrent-mark-sweep perm gen total 307200K, used 143429K [0x00000007ed400000, 0x0000000800000000, 0x0000000800000000)
2018-04-16T14:23:47.037+0800: 356596.434: [GC2018-04-16T14:23:47.037+0800: 356596.434: [ParNew2018-04-16T14:23:47.049+0800: 356596.446: [SoftReference, 0 refs, 0.0000370 secs]2018-04-16T14:23:47.049+0800: 356596.446: [WeakReference, 26 refs, 0.0000130 secs]2018-04-16T14:23:47.049+0800: 356596.446: [FinalReference, 43 refs, 0.0000470 secs]2018-04-16T14:23:47.049+0800: 356596.446: [PhantomReference, 0 refs, 0.0000090 secs]2018-04-16T14:23:47.049+0800: 356596.446: [JNI Weak Reference, 0.0000100 secs]
Desired survivor size 48791552 bytes, new threshold 10 (max 10)
- age 1: 4083168 bytes, 4083168 total
- age 2: 1029504 bytes, 5112672 total
- age 3: 362720 bytes, 5475392 total
- age 4: 28200 bytes, 5503592 total
- age 5: 56616 bytes, 5560208 total
- age 6: 8384 bytes, 5568592 total
- age 7: 12944 bytes, 5581536 total
- age 8: 7328 bytes, 5588864 total
- age 9: 8472 bytes, 5597336 total
- age 10: 11560 bytes, 5608896 total
: 1912541K->8400K(2001856K), 0.0122020 secs] **2171686K->267554K**(4099008K), 0.0124480 secs] [Times: user=0.05 sys=0.00, real=0.01 secs]
Heap after GC invocations=655 (full 1):
par new generation total 2001856K, used 8400K [0x00000006ed400000, 0x000000076d400000, 0x000000076d400000)
eden space 1906560K, 0% used [0x00000006ed400000, 0x00000006ed400000, 0x00000007619e0000)
from space 95296K, 8% used [0x00000007676f0000, 0x0000000767f24158, 0x000000076d400000)
to space 95296K, 0% used [0x00000007619e0000, 0x00000007619e0000, 0x00000007676f0000)
concurrent mark-sweep generation total 2097152K, used 259153K [0x000000076d400000, 0x00000007ed400000, 0x00000007ed400000)
concurrent-mark-sweep perm gen total 307200K, used 143429K [0x00000007ed400000, 0x0000000800000000, 0x0000000800000000)
}老年代確實降下來了：2171686K->267554K
但是新生代，為何頻繁回收呢？
當時線程gclog-鏈接: https://pan.baidu.com/s/1jz5I... 密碼: ddrz
暫時自己的解決辦法是擴大新生代為3g
有沒有遇到過這類問題的？
1、從第一圖和第三圖的曲線看，CPU高-->頻繁ygc造成
2、通常調(diào)整survivorRatio的效益不是那么明顯，整體收益不如調(diào)整新生代大小。從gc日志看，年老代最大的時候才使用600多M，是可以選擇擴大新生代大小再觀察下是否還有問題。
3、新生代頻繁gc，這個跟你的服務性質(zhì)有關。提供查詢，導出等功能，導出功能的話，看實現(xiàn)的機制，如果是一次性load到內(nèi)存計算，最后再一次性寫到response，那么這段期間會占用內(nèi)存，如果同一時刻再多來幾次同類的導出請求，則新生代垃圾回收壓力大。從年老代使用峰值看，沒有內(nèi)存泄露，也就是這些對象基本在幾次ygc之后就回收了。于是就是新生代不斷產(chǎn)生對象，不斷回收部分，不斷晉升到年老代。之所以頻繁ygc，主要是垃圾回收速度跟不上新生對象創(chuàng)建速度導致。
survivor 是故意設置小一點，讓回收不掉的對象，加速進入到老年代
光看內(nèi)存日志幾乎不可能找到原因。必須結(jié)合訪問日志和業(yè)務日志，定位問題可能出現(xiàn)在哪塊業(yè)務邏輯上，然后再去在代碼中排查。
新生代回收頻繁比較正常，朝生夕死。
看到有個參數(shù)：
-XX:SurvivorRatio=20
Survivor區(qū)是否有點小了？
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