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1、线上GC异常排查线上GC异常排查1现象最近去线上看了下gc情况，发现出现频繁的fullGC。问题如下图:fir阳阳WJT55555559-912335-74699999912044B7&1BElCT3CTICT3inOOOOO0757575話75巧7S7515s9111112490-808792293B73173234&29-ual81618181slel8181el8181的slslMeleln95.6835.68沾聒血95.6605沾B35.95.6895.68券点北血95.6B95,6S北血958:statCCS9.ll96.1195119.ll96.1196.1195.1196.119
2、6.1145.1196.11 96.IL95.1196.11 %1145.1196.11 %11-gcutilY5C1295BL295B12358L295E-1235E12358128561235912S59129591235912S591235912359128591295912359129591541ieeeYGCT165JB5165.765165.7B5165.?E5165.765165.765165l?E5165.776165.776165.776165.776165.776165.776 165.776165.776 15,776165.776 165.77&FGC135305135
3、30513530513530513530513530613530S13530713530713530713530713530713S3QB13530B135309135309135309135309FKT395&2.461395B2.461395B2.46139562.461 395B246139562.461GCTHM取2163974B.2263974E.2263974B.22639746.3163974E.22&39583.743e?4B,B40395B3.185395E3h询539583.085395B9.ee33563.沖539563F2弼395B33T6395&3.51639563,
4、316395B3.3K395B3J1639746r8tl3B?4B.8$13即4E冷百13974er8il30745.86139745.8=23974BJ5239749.892鶉碣上923974E.G5239749.82gc情况.jpg然后查看了下GC原因，如下:2.分析；?J2?42,?42?12M2.?J2J42?42.742?J2?42?42?12742.7J2J42.742.742.?42?Jisa11.51L3Wl&.l-?17.M勢.廿21.22.732*.牌25.7-12&.es曲.廿知.14316137.5轴.昶41.9：皈無47.1(if创Bl.5701.5761,57Bl.
5、57Bl.H61,57B1.S7Bl.761,57Bl.=781.Bl,5701.57Bl.；7BL,57B1.E761.7Bl.57Bl.=7-1$Fl95.6895.6395.6895.SS95.6395.6895.6996.6395.6895.6S95.6395.689S.G395.6395.689S.GS95.6395.6895.63CfiRS-gtCoue1:411000佩预TFOC12期15,4941翡时91293716S.494135删129371粘.曲4135&3912期165.4941354912837IB.494135B4B13837Iffl.JW13SHB128刃165.
6、49413541nanU5.4Mns&41120371M.49413EHL12fln165.49413534113037165.494135&41120371M.4MU5H212W165.49413564213037IB.494135M31283JIM.49413S843-：gC原因图.U037165.494135943129371M.4M135M312837165.勒13534113937IK.494135944=KT3557.639-7.6H395Z-7.61-39:.6n3-7.3S53乃軒.的5即为丁.勺茁39-7.933;-7.93?四禽.弼39Z-7.93395JB2北3951-9
7、37C39UB37(pg39:：-B37639B37(39=5&.3739:&75GGCT.(KC3S6?5.1STCHSinitialllark39671.167CHSInitialHark3967ar167(USInitialHark39672.197NoOC39671.339CHSFinalRenark站阻冷御015FmalRenark39673.433CHSInitialhark39673.433CMSInitialHark396,433CHSInitioHark3067.433CMSInitialMark39673.433015InitialHark站阻订弭(USFmalRensrk
8、39671531CHSFinal龍rsk395,364CHSIiLtialHark却W笳4(USnark39673.354CMSInitialMark39&Tjr364CHSIiLtialMark396.864CHSInitioHark2；躺克.鮎斗CHSInitialMark39&7J25&CHSFutalRenarkMGCKDooOCNNNcccccccccc_cc-uGG-uG6-uHu*G-H-GG-uG6-uQOOD-OO-QOOOOOOOOONNNNNNNNXNNNNNNN根据上面两张图，可以看出主要是老年代进行了频繁的CMSGC。而CMS回收的前提条件就是老年代达到一定的容量。这
9、个容量可以数CMSInitiatingOccupancyFraction进行设置。本项目的jvm配置如下：-Xms4096m-Xmx4096m-Xmn3072m-Xss1024K-XX:PermSize=256m-XX:MaxPermSize=512m-XX:ParalleXX:+UseConcMarkSweepGC-XX:+UseParNewGC-XX:+UseCMSCompactAtFullCollection-XX:CMSInitiatingOccupancyFraction=80根据上面配置可以看出，老年代的容量为1G,且老年代达到80%的时候进行CMS回收。而根据上图可以发现老年代的
10、占用率一直在,每次回收基本上都没有释放空间。所以一直在频繁的出发CMS回收算法。3排查依据上面的推断，使用命令jmap-dump:live,format=b,file=heap.hprofpid触发fullGC,并dump内存快照。因为本次内存主要是老年代频繁GC导致的，而且每次回收都没有回收到有效空间。所以才直接加上live属性，防止年轻代对象干扰结果。然后使用mat分析内存泄漏如下：iOven/ewHIHistogram很ulistobjectsseectioriofStringBuider，ulistobjectselectionofThreadLocalJCassNaneObjects
11、ShaowHeapstainedHeapJ0diarSS+,191674.81怖=674.81MBOjava.hnglhread刚0.D9MB=630.56MB0java.lang.ThreadLocalSHireadLocalMap1,9280.04MB=63031MB9java.hng.ThreadL)calSTlirefldLocalMap$Ertry1r928024MB=63027MB=629.68MB3java.lang.StrngBuider1110.02MB=514.02MBGbyteQ112636938MB=6938MB0jawa.hng.Object35,1533.13MB=
12、61.18MB3java.lang.Strng586,92213.43MB=5939MBGjava.utiLArrayLst31,5510.72MB=44.34MB3sun.mk.Launcher$AppClas5Lodder10.00MB=35.41MBGcombj58spat.sbdient.connmuiiication.NIOChan.40.00MB=32.00MBGjava.util.Vectcr5r3790.16MB=31.56MB0java.niQ.HeapByteEiffer4580.02MB=28.09MB芒ictir卜厂1Deel1firmFuiD_irD7heap直方图根
13、据图中shallowheap和Retainedheap可看出占用内存最大的就是char数组。而thread、threadlocal还有StringBuilder都可能指向的就是char数组对象。下图也验证了这个猜想。5匸LlUFYIIS.UbEliLU11JIUUJCLL33CICLLIUIIUlJLlbUUIIUCLU113LUUJCl.JpCICL.IUIIUlIIKClLULnpIIIIClassName手ShallowHeapRetainedHeapjava.ang.Thread0x788b8Z9b0SCFasyncworker26-ttiread-11ThreadO.ODME1.77MBig沁ang.Thread0x787a97c50SCFyncworkef11-tirec-9hreadO.ODMB1.77MBjava.ang.Thread0x783728998SCFasynuvork&r14-tliread-5HireadO.ODME1.77MB.dva.ang.Thad0x787a968tOSCFancwofer15-tac-BhreadO.ODMB1.76MB:.ava.ang
