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msm(CentOS 6)及jvm虚拟机性能监控(04)_recv

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為什么80%的碼農都做不了架構師？>>> ??

JVM

JVM內存管理--運行時數據區

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JVM大體由五個部分組成，分別為JVM Stack、Native Stack、Program Counter Register、Java Heap、Method Area。其中JVM Stack、Native Stack、Program Counter Register為每個線程私有，然而Java Heap、Method Area為所有線程共享。每個對象都是由它對應的內部數據和外置的、可以由類提供共享給各個對象的各個方法組成。方法是外部代碼，由每個實例化出來的對象可以調用的，而 Java Heap主要是用來存放這些對象的，對于JVM來說，Java Heap所占據的空間最大。

兩類JVM管理的內存

JVM管理的內存段可以分為兩大類：線程共享內存和線程私有內存。

線程共享內存

Method Area : 存儲jvm加載的class、常量、靜態變量、即時編譯器編譯后的代碼等。
Java Heap ：存儲java的所有對象實例、數組等。

線程私有內存

Program Counter Register ：每個線程都有自己的計數寄存器，存儲當前線程執行字節碼的地址。
JVM Stack ： jvm會為每個運行線程分配一個棧區，線程調用方法時和方法返回時會進行入棧和出棧操作。
Native Stack ：與 jvm stack 類似，只不過此區域是為調用本地方法服務。

Java Heap Size Options

http://docs.oracle.com/cd/E13222_01/wls/docs81/perform/JVMTuning.html

TaskOptionRecommended Value

Setting the New generation heap size	-XX:NewSize	Set this value to a multiple of 1024 that is greater than 1MB. As a general rule, set?-XX:NewSize?to be one-fourth the size of the maximum heap size. Increase the value of this option for larger numbers of short-lived objects. Be sure to increase the New generation as you increase the number of processors. Memory allocation can be parallel, but garbage collection is not parallel.
Setting the maximum New generation heap size	-XX:MaxNewSize	Set this value to a multiple of 1024 that is greater than 1MB
Setting New heap size ratios	-XX:SurvivorRatio	The New generation area is divided into three sub-areas: Eden, and two survivor spaces that are equal in size. Configure the ratio of the Eden/survivor space size. Try setting this value to 8, and then monitor your garbage collection.
Setting minimum heap size	-Xms	Set the minimum size of the memory allocation pool. Set this value to a multiple of 1024 that is greater than 1MB. As a general rule, set minimum heap size (-Xms)?equal to the maximum heap size (-Xmx)?to minimize garbage collections.
Setting maximum heap size	-Xmx	Set the maximum size of the memory allocation pool. Set this value to a multiple of 1024 that is greater than 1MB.

參數說明

-Xmx	young generation 和 old generation總共可用的最大空間
-Xms	young generation 和 old genertaion二者初始空間。沒分配的叫做reserved，再沒有的話，向內核申請，如果內核沒有內存的話，想辦法使用LRU算法從其他程序里騰出內存給它。
-XX:NewSize	young generation初始空間
-XX:MaxNewSize	young generation最大空間
-XX:PermSize	permanent generation初始空間
-XX:MaxPermSize	permanent generation最大空間

參數 -Xmx 和 -Xms 經常使用，使用的方式是，在jvm啟動時將該參數及其對應的值傳遞給jvm，具體合適傳遞哪？一般來講，啟動tomcat的話，在catalina.sh中有兩個環境變量：CATALINA_OPTS、JAVA_OPTS。CATALINA_OPTS僅對啟動運行tomcat實例的jvm虛擬機有效。JAVA_OPTS對本機上的所有JVM有效。如果機器上不僅僅有tomcat實例，建議使用CATALINA_OPTS。可以直接編輯catalina.sh，也可以使用命令設定，例如：

$ export CALALINA_OPTS="-Xmx256m"

The memory structure of a JVM process

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對于Java Heap而言，分為 young generation、old generation、permanent generation三個區域。young generation又可分為 to、from、eden三個子區域，之所以分成這三個子區域主要原因是在young generation上面的垃圾收集算法或者叫垃圾收集器，會分別實現young generation、old generation、permanent generation三個區域移動對象之后，完成gc。創建的對象在young generation中過了一定存活時間以后，依然被采用的，那么該對象就會從young generation挪到old generation。如果有些對象創建以后不會被刪除的，那么該對象就會被存放在permanent generation。

JVM Memory Handling

When the JVM starts, the host OS assigns a dedicated（?專注的，投入的; 獻身的; 專用的;） memory space to that VM【vm會從操作系統那里取到一定內存空間】
The VM allocates memory to the application within that dedicated memory space【vm會按照特定的格式劃分區段，之所以劃分是為了讓垃圾回收器完成垃圾回收】
The VM frees memory automatically via（經過; 通過，憑借; 取道;） garbage collectors
Garbage Collection is an expensive（昂貴的，花錢多的; 豪華的;）?algorithm

Garbage Collectors

如果不考慮permanent generation的話，內存區域大體可以分為以下三個部分：

Eden Space： where objects ara born
Survivor Spaces : Where objects mature（成熟），contains to, from。
Tenured Space : Where objects grow old and die

其中 Eden Space 和 Survivor組成的是young generation。Tenured Space表示old generation。

JVM Memory Layout

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New/Young - Recently created object

Old - Long lived object

Perm - JVM classes and methods

Garbage Collector

Collecting unsed java object
Cleaning memory
Minor GC : Collection memory in New/Young generation
Major GC( Full GC ) :?Collection memory in old generation

young generation和old generation的gc的頻率不同，算法也不同。不斷地執行垃圾回收，騰出空間，主要是針對young generation實現的，對young generation實現垃圾回收的叫做Minor GC，對old generation實現垃圾回收的叫做Major GC。java當中垃圾回收器本身有多種實現方案，即便是Minor GC、Major GC。

Minor GC

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注意垃圾回收不是實時進行的，而是積攢到一定的量才會進行操作。執行垃圾回收的過程中其他的線程無法工作，因為其非常消耗資源，會占據整個cpu，這種垃圾回收算法也稱之為stop the world，這也就是我們日常生活中使用andriod手機假死的原因。與此不同的蘋果ios，是用object-c開發的，程序直接運行在硬件之上，其一：性能好，不用虛擬機解釋、運行代碼；其二：object-c自己可以實現內存管理，內存回收是及時的，不存在垃圾回收的過程。

Major GC

Old Generation
Mark and compact
Slow ( 1st - goes through the entire heap, marking unreachable objects. 2nd?- unreachable objects are compacted )。

對于old generation的垃圾回收一般用Mark and compact( 標記清除算法)實現的，這種垃圾回收的工作恒比較慢，分為兩個階段，第一個步要遍歷整個堆內存，標記不再使用的對象，第二步將不再使用的對象一起打包一次性回收。Major GC發生的過程才是真正的stop the world發生的過程，一般發聲Major GC原因是old generation 中的對象過多，而大多數的java程序發生Major GC 很少，因為對象被送到old generation區域的少之又少，在到達old generation之前已經被回收了。一旦發聲full gc，就需要等待該過程完成，可能也需要手動釋放一些堆空間。

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根據業務運行模型和內存使用方式來指定不同區域的大小。

性能監控工具

常見問題：OutOfMemoryError：內存不足。引發該問題的原因有內存泄漏（代碼問題）、線程死鎖、鎖競爭（Lock Contention）、Java消耗過多的CPU等等。

jps

jps( java machine process status tool )

監控jvm進程狀態信息。jps本身也是使用java開發的，所以它本身也運行這一個java進程。

jps [options] [hostid]-m ：輸出傳入main方法的參數-l ：顯示main類或者jar文件的完全限定名稱（也就是完整類名）-v ：顯示jvm指定的參數（也就是啟動jvm的時候傳遞了哪些參數給它） [root@app1 ~]# jps 3808 Jps 784 Bootstrap [root@app1 ~]# jps -m -l # 查看真正啟動jvm的程序或者類是什么 3730 sun.tools.jps.Jps -m -l 784 org.apache.catalina.startup.Bootstrap start [root@app1 ~]# [root@app1 ~]# jps -m -l -v 784 org.apache.catalina.startup.Bootstrap start -Djava.util.logging.config.file=/usr/soft/apache-tomcat-7.0.76/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Xms2048m -Xmx32768m -Xss4096K -XX:PermSize=1024m -XX:MaxPermSize=2048m -Djdk.tls.ephemeralDHKeySize=2048 -Djava.endorsed.dirs=/usr/soft/apache-tomcat-7.0.76/endorsed -Dcatalina.base=/usr/soft/apache-tomcat-7.0.76 -Dcatalina.home=/usr/soft/apache-tomcat-7.0.76 -Djava.io.tmpdir=/usr/soft/apache-tomcat-7.0.76/temp 4056 sun.tools.jps.Jps -m -l -v -Denv.class.path=.:/usr/jdk64/jdk1.7.0_67/lib/dt.jar:/usr/jdk64/jdk1.7.0_67/lib/tools.jar -Dapplication.home=/usr/jdk64/jdk1.7.0_67 -Xms8m [root@app1 ~]#

jstack

用于查看某個java進程內的線程堆棧信息。

jstack [options] pid-l long listings 輸出完整的鎖信息。可以指定輸出某一項。-m 混合模式，即會輸出java堆棧及c/c++堆棧信息

哪一個java進程最耗cpu？ top->jstack

jmap

jmap (jvm mamory map) ：查看堆內存使用情況。

jmap [options] pid-heap :詳細輸出堆內存空間使用狀態信息-histo[:live] :查看堆內存中的對象數目、大小統計結果。 [root@app1 ~]# jmap Usage:jmap [option] <pid>(to connect to running process)jmap [option] <executable <core>(to connect to a core file)jmap [option] [server_id@]<remote server IP or hostname>(to connect to remote debug server)where <option> is one of:<none> to print same info as Solaris pmap-heap to print java heap summary-histo[:live] to print histogram of java object heap; if the "live"suboption is specified, only count live objects-permstat to print permanent generation statistics-finalizerinfo to print information on objects awaiting finalization-dump:<dump-options> to dump java heap in hprof binary formatdump-options:live dump only live objects; if not specified,all objects in the heap are dumped.format=b binary formatfile=<file> dump heap to <file>Example: jmap -dump:live,format=b,file=heap.bin <pid>-F force. Use with -dump:<dump-options> <pid> or -histoto force a heap dump or histogram when <pid> does notrespond. The "live" suboption is not supportedin this mode.-h | -help to print this help message-J<flag> to pass <flag> directly to the runtime system [root@app1 ~]# jmap 784 Attaching to process ID 784, please wait... Debugger attached successfully. Server compiler detected. JVM version is 24.65-b04 0x0000000000400000 7K /usr/jdk64/jdk1.7.0_67/bin/java 0x00000031f8400000 153K /lib64/ld-2.12.so 0x00000031f8800000 22K /lib64/libdl-2.12.so 0x00000031f8c00000 1883K /lib64/libc-2.12.so 0x00000031f9000000 142K /lib64/libpthread-2.12.so 0x00000031f9400000 46K /lib64/librt-2.12.so 0x00000031f9800000 585K /lib64/libm-2.12.so 0x00000031fa800000 91K /lib64/libgcc_s-4.4.7-20120601.so.1 0x00000031fd800000 111K /lib64/libresolv-2.12.so 0x00007f28b41eb000 26K /lib64/libnss_dns-2.12.so 0x00007f28bc172000 477K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libt2k.so 0x00007f2934178000 512K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libfontmanager.so 0x00007f293c1ea000 36K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/headless/libmawt.so 0x00007f297c11f000 755K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libawt.so 0x00007f29e0bf2000 250K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libsunec.so 0x00007f29e123a000 44K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libmanagement.so 0x00007f29e1442000 112K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libnet.so 0x00007f29e1659000 89K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libnio.so 0x00007f331872f000 120K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libzip.so 0x00007f331894a000 64K /lib64/libnss_files-2.12.so 0x00007f3318b61000 214K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libjava.so 0x00007f3318d8c000 63K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/libverify.so 0x00007f331939b000 14853K /usr/jdk64/jdk1.7.0_67/jre/lib/amd64/server/libjvm.so 0x00007f331a212000 103K /usr/jdk64/jdk1.7.0_67/lib/amd64/jli/libjli.so [root@app1 ~]# jmap -heap 784 Attaching to process ID 784, please wait... Debugger attached successfully. Server compiler detected. JVM version is 24.65-b04using thread-local object allocation. Parallel GC with 18 thread(s) # 垃圾收集算法Heap Configuration:MinHeapFreeRatio = 0MaxHeapFreeRatio = 100MaxHeapSize = 34359738368 (32768.0MB)NewSize = 1310720 (1.25MB)MaxNewSize = 17592186044415 MBOldSize = 5439488 (5.1875MB)NewRatio = 2SurvivorRatio = 8PermSize = 1073741824 (1024.0MB)MaxPermSize = 2147483648 (2048.0MB)G1HeapRegionSize = 0 (0.0MB)Heap Usage: PS Young Generation Eden Space:capacity = 4660920320 (4445.0MB)used = 3455457416 (3295.380989074707MB)free = 1205462904 (1149.619010925293MB)74.13680515353671% used From Space:capacity = 6815744 (6.5MB)used = 6811632 (6.4960784912109375MB)free = 4112 (0.0039215087890625MB)99.93966909555289% used To Space:capacity = 143130624 (136.5MB)used = 0 (0.0MB)free = 143130624 (136.5MB)0.0% used PS Old Generationcapacity = 1431830528 (1365.5MB)used = 275154128 (262.4074249267578MB)free = 1156676400 (1103.0925750732422MB)19.216947999030232% used PS Perm Generationcapacity = 1073741824 (1024.0MB)used = 91206560 (86.98135375976562MB)free = 982535264 (937.0186462402344MB)8.494272828102112% used42967 interned Strings occupying 5456928 bytes. [root@app1 ~]# jmap -histo:live 784 # 詳細顯示java堆空間中的每一個對象num #instances #bytes class name ----------------------------------------------1: 238261 31749640 [C2: 48744 30171672 [B3: 152303 23372728 <constMethodKlass>4: 152303 19508224 <methodKlass>5: 13376 16932432 <constantPoolKlass>6: 13376 10056128 <instanceKlassKlass>7: 10801 9292768 <constantPoolCacheKlass>8: 233736 7479552 java.lang.String9: 43674 4785504 [Ljava.lang.Object;10: 6485 3820120 <methodDataKlass>11: 25037 3605328 java.lang.reflect.Method12: 14301 3046232 java.lang.Class13: 47576 3044864 java.util.LinkedHashMap$Entry14: 13333 2737448 [Ljava.util.HashMap$Entry;15: 54334 2608032 java.util.concurrent.ConcurrentHashMap$HashEntry16: 4380 2191472 [I17: 21963 2021432 [[I18: 38640 1854720 java.util.HashMap$Entry19: 17256 1794624 java.net.URL20: 18236 1309960 [S21: 14735 1296680 java.util.LinkedHashMap22: 30648 1225920 java.util.ArrayList23: 5079 1066472 [Ljava.util.concurrent.ConcurrentHashMap$HashEntry;24: 14417 1038024 org.apache.xerces.dom.DeferredTextImpl25: 12418 894096 org.apache.catalina.loader.ResourceEntry26: 14042 835776 [Ljava.lang.String;27: 6231 797568 org.apache.jasper.compiler.Node$TemplateText28: 7247 753688 org.apache.xerces.dom.DeferredElementImpl29: 7749 681912 org.apache.jasper.compiler.Mark30: 13745 659760 java.lang.ref.WeakReference31: 10086 645504 org.apache.xerces.dom.DeferredAttrImpl32: 11230 628880 java.lang.ref.SoftReference33: 8399 604728 java.util.HashMap 。。。省略

jhat

jhat (jvm heap analysis tool)，更多用于代碼中的運行狀況。

[root@app1 ~]# jhat ERROR: No arguments supplied Usage: jhat [-stack <bool>] [-refs <bool>] [-port <port>] [-baseline <file>] [-debug <int>] [-version] [-h|-help] <file>-J<flag> Pass <flag> directly to the runtime system. Forexample, -J-mx512m to use a maximum heap size of 512MB-stack false: Turn off tracking object allocation call stack.-refs false: Turn off tracking of references to objects-port <port>: Set the port for the HTTP server. Defaults to 7000-exclude <file>: Specify a file that lists data members that shouldbe excluded from the reachableFrom query.-baseline <file>: Specify a baseline object dump. Objects inboth heap dumps with the same ID and same class willbe marked as not being "new".-debug <int>: Set debug level.0: No debug output1: Debug hprof file parsing2: Debug hprof file parsing, no server-version Report version number-h|-help Print this help and exit<file> The file to readFor a dump file that contains multiple heap dumps, you may specify which dump in the file by appending "#<number>" to the file name, i.e. "foo.hprof#3".All boolean options default to "true" [root@app1 ~]#

jstat

jstat (jvm統計監測工具)

[root@app1 ~]# jstat invalid argument count Usage: jstat -help|-optionsjstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]] # option為必選項Definitions:<option> An option reported by the -options option<vmid> Virtual Machine Identifier. A vmid takes the following form:<lvmid>[@<hostname>[:<port>]]Where <lvmid> is the local vm identifier for the targetJava virtual machine, typically a process id; <hostname> isthe name of the host running the target Java virtual machine;and <port> is the port number for the rmiregistry on thetarget host. See the jvmstat documentation for a more completedescription of the Virtual Machine Identifier.<lines> Number of samples between header lines.<interval> Sampling interval. The following forms are allowed:<n>["ms"|"s"]Where <n> is an integer and the suffix specifies the units as milliseconds("ms") or seconds("s"). The default units are "ms".<count> Number of samples to take before terminating.-J<flag> Pass <flag> directly to the runtime system. [root@app1 ~]# jstat -gc 784 S0C S1C S0U S1U EC EU OC OU PC PU YGC YGCT FGC FGCT GCT 129024.0 512.0 0.0 0.0 4153856.0 61658.6 1398272.0 120259.0 1048576.0 88442.2 23 1.005 2 0.641 1.646 [root@app1 ~]# S0C,S1C,S0U,S1U：C表示容量，U表示已用量。 EC,EU：eden區域的容量和已用量。 OC,OU PC,PU YGC,YGT:表示新生代的gc次數和耗時 FGC,FGCT:表示FULL GC的次數和耗時 GCT:GC總耗時

jconsole

jvisualvm

轉載于:https://my.oschina.net/qzhli/blog/903399

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