Tomcat 性能优化

[root@t1 ~]#java -version
java version "1.8.0_271"
Java(TM) SE Runtime Environment (build 1.8.0_271-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.271-b09, mixed mode)

[root@centos8 ~]#cat Heap.java
public class Heap {
    public static void main(String[] args){
        //返回JVM试图使用的最大内存,字节单位
        long max = Runtime.getRuntime().maxMemory();
        //返回JVM初始化总内存
        long total = Runtime.getRuntime().totalMemory();
        
        System.out.println("max="+max+"字节\t"+(max/(double)1024/1024)+"MB");
        System.out.println("total="+total+"字节\t"+(total/(double)1024/1024)+"MB");
    }
}

[root@centos8 ~]#javac Heap.java
[root@centos8 ~]#java -classpath . Heap
ax=243269632字节 232.0MB
total=16252928字节 15.5MB

#JDK-8的执行结果
[root@centos8 ~]#java -XX:+PrintGCDetails Heap
max=243269632字节 232.0MB
total=16252928字节 15.5MB
Heap
def new generation total 4928K, used 530K [0x00000000f1000000,
0x00000000f1550000, 0x00000000f6000000)
eden space 4416K, 12% used [0x00000000f1000000, 0x00000000f1084a60,
0x00000000f1450000)
from space 512K, 0% used [0x00000000f1450000, 0x00000000f1450000,
0x00000000f14d0000)
to space 512K, 0% used [0x00000000f14d0000, 0x00000000f14d0000,
0x00000000f1550000)
tenured generation total 10944K, used 0K [0x00000000f6000000,
0x00000000f6ab0000, 0x0000000100000000)
the space 10944K, 0% used [0x00000000f6000000, 0x00000000f6000000,
0x00000000f6000200, 0x00000000f6ab0000)
Metaspace used 2525K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 269K, capacity 386K, committed 512K, reserved 1048576K

[root@centos8 ~]#echo "scale=2;(4928+10944)/1024" |bc
15.50
#说明年轻代+老年代占用了所有heap空间, Metaspace实际不占heap空间,逻辑上存在于Heap

#JDK-11的执行结果
[root@ubuntu2204 ~]#java -version
java version "11.0.19" 2023-04-18 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.19+9-LTS-224)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.19+9-LTS-224, mixed mode)
[root@ubuntu2204 ~]#java -XX:+PrintGCDetails Heap
[0.002s][warning][gc] -XX:+PrintGCDetails is deprecated. Will use -Xlog:gc*
instead.
[0.012s][info ][gc,heap] Heap region size: 1M
[0.027s][info ][gc ] Using G1
[0.027s][info ][gc,heap,coops] Heap address: 0x00000000e1a00000, size: 486 MB,
Compressed Oops mode: 32-bit
max=509607936字节 486.0MB
total=33554432字节 32.0MB
[0.331s][info ][gc,heap,exit ] Heap
[0.332s][info ][gc,heap,exit ] garbage-first heap total 32768K, used 1024K
[0x00000000e1a00000, 0x0000000100000000)
[0.332s][info ][gc,heap,exit ] region size 1024K, 2 young (2048K), 0
survivors (0K)
[0.332s][info ][gc,heap,exit ] Metaspace used 4823K, capacity 4894K,
committed 5120K, reserved 1056768K
[0.332s][info ][gc,heap,exit ] class space used 406K, capacity 424K,
committed 512K, reserved 1048576K

查看java命令标准选项
[root@centos ~]#java
Usage: java [-options] class [args...]
(to execute a class)
or java [-options] -jar jarfile [args...]
(to execute a jar file)
where options include:
-d32 use a 32-bit data model if available
-d64 use a 64-bit data model if available
-server to select the "server" VM
The default VM is server.
-cp <class search path of directories and zip/jar files>
-classpath <class search path of directories and zip/jar files>
A : separated list of directories, JAR archives,
and ZIP archives to search for class files.
-D<name>=<value>
set a system property
-verbose:[class|gc|jni]
enable verbose output
-version print product version and exit
-version:<value>
Warning: this feature is deprecated and will be removed
in a future release.
require the specified version to run
-showversion print product version and continue
-jre-restrict-search | -no-jre-restrict-search
Warning: this feature is deprecated and will be removed
in a future release.
include/exclude user private JREs in the version search
-? -help print this help message
-X print help on non-standard options #非标准选项
-ea[:<packagename>...|:<classname>]
-enableassertions[:<packagename>...|:<classname>]
enable assertions with specified granularity
-da[:<packagename>...|:<classname>]
-disableassertions[:<packagename>...|:<classname>]
disable assertions with specified granularity
-esa | -enablesystemassertions
enable system assertions
-dsa | -disablesystemassertions
disable system assertions
-agentlib:<libname>[=<options>]
load native agent library <libname>, e.g. -agentlib:hprof
see also, -agentlib:jdwp=help and -agentlib:hprof=help
-agentpath:<pathname>[=<options>]
load native agent library by full pathname
-javaagent:<jarpath>[=<options>]
load Java programming language agent, see java.lang.instrument
-splash:<imagepath>
show splash screen with specified image
See http://www.oracle.com/technetwork/java/javase/documentation/index.html for
more details.
[root@t1 ~]#

#查看java的非标准选项
[root@centos8 ~]#java -X
-Xmixed mixed mode execution (default)
-Xint interpreted mode execution only
-Xbootclasspath:<directories and zip/jar files separated by :>
set search path for bootstrap classes and resources
-Xbootclasspath/a:<directories and zip/jar files separated by :>
append to end of bootstrap class path
-Xbootclasspath/p:<directories and zip/jar files separated by :>
prepend in front of bootstrap class path
-Xdiag show additional diagnostic messages
-Xnoclassgc disable class garbage collection
-Xincgc enable incremental garbage collection
-Xloggc:<file> log GC status to a file with time stamps
-Xbatch disable background compilation
-Xms<size> set initial Java heap size
-Xmx<size> set maximum Java heap size
-Xss<size> set java thread stack size
-Xprof output cpu profiling data
-Xfuture enable strictest checks, anticipating future default
-Xrs reduce use of OS signals by Java/VM (see documentation)
-Xcheck:jni perform additional checks for JNI functions
-Xshare:off do not attempt to use shared class data
-Xshare:auto use shared class data if possible (default)
-Xshare:on require using shared class data, otherwise fail.
-XshowSettings show all settings and continue
-XshowSettings:all
show all settings and continue
-XshowSettings:vm show all vm related settings and continue
-XshowSettings:properties
show all property settings and continue
-XshowSettings:locale
show all locale related settings and continue
The -X options are non-standard and subject to change without notice.

#查看所有不稳定选项的当前生效值
[root@centos8 ~]#java -XX:+PrintFlagsFinal
[Global flags]
intx ActiveProcessorCount = -1
{product}
uintx AdaptiveSizeDecrementScaleFactor = 4
{product}
uintx AdaptiveSizeMajorGCDecayTimeScale = 10
{product}
uintx AdaptiveSizePausePolicy = 0
{product}
uintx AdaptiveSizePolicyCollectionCostMargin = 50
{product}
uintx AdaptiveSizePolicyInitializingSteps = 20
{product}
uintx AdaptiveSizePolicyOutputInterval = 0
{product}
uintx AdaptiveSizePolicyWeight = 10
{product}
uintx AdaptiveSizeThroughPutPolicy = 0
{product}
.......

#查看所有不稳定选项的默认值
[root@centos8 ~]#java -XX:+PrintFlagsInitial
[Global flags]
intx ActiveProcessorCount = -1
{product}
uintx AdaptiveSizeDecrementScaleFactor = 4
{product}
uintx AdaptiveSizeMajorGCDecayTimeScale = 10
{product}
uintx AdaptiveSizePausePolicy = 0
{product}
uintx AdaptiveSizePolicyCollectionCostMargin = 50
{product}
uintx AdaptiveSizePolicyInitializingSteps = 20
{product}
.......

#查看当前命令行的使用的选项设置
[root@centos8 ~]#java -XX:+PrintCommandLineFlags
-XX:InitialHeapSize=15598528 -XX:MaxHeapSize=249576448 -
XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops
-XX:+UseParallelGC
#上面的-XX:+UseParallelGC 说明当前使用Parallel Scavenge + Parallel Old

#默认JVM试图分配最大内存的总内存的1/4,初始化默认总内存为总内存的1/64
[root@centos8 ~]#cat Heap.java
public class Heap {
    public static void main(String[] args){
        //返回JVM试图使用的最大内存,字节单位
        long max = Runtime.getRuntime().maxMemory();
        //返回JVM初始化总内存
        long total = Runtime.getRuntime().totalMemory();
        System.out.println("max="+max+"字节\t"+(max/(double)1024/1024)+"MB");
        System.out.println("total="+total+"字节\t"+(total/(double)1024/1024)+"MB");
    }
}

#编译生成class文件
[root@centos8 ~]#javac Heap.java

#通过$CLASSPATH指定类文件路径,否则无法找到类,也可以通过 java -cp /path指定类路径
[root@centos8 ~]#echo $CLASSPATH
/usr/local/jdk/lib/:/usr/local/jdk/jre/lib/

[root@centos8 ~]#cp Heap.class /usr/local/jdk/lib

#查看当前内存默认值
[root@centos8 ~]#java -XX:+PrintGCDetails Heap

max=243269632字节 232.0MB
total=16252928字节 15.5MB
Heap
def new generation total 4928K, used 530K [0x00000000f1000000,
0x00000000f1550000, 0x00000000f6000000)
eden space 4416K, 12% used [0x00000000f1000000, 0x00000000f1084a60,
0x00000000f1450000)
from space 512K, 0% used [0x00000000f1450000, 0x00000000f1450000,
0x00000000f14d0000)
to space 512K, 0% used [0x00000000f14d0000, 0x00000000f14d0000,
0x00000000f1550000)
tenured generation total 10944K, used 0K [0x00000000f6000000,
0x00000000f6ab0000, 0x0000000100000000)
the space 10944K, 0% used [0x00000000f6000000, 0x00000000f6000000,
0x00000000f6000200, 0x00000000f6ab0000)
Metaspace used 2525K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 269K, capacity 386K, committed 512K, reserved 1048576K

#指定内存空间
[root@centos8 ~]#java -Xms1024m -Xmx1024m -XX:+PrintGCDetails Heap
max=1037959168字节 989.875MB
total=1037959168字节 989.875MB
Heap
def new generation total 314560K, used 11185K [0x00000000c0000000,
0x00000000d5550000, 0x00000000d5550000)
eden space 279616K, 4% used [0x00000000c0000000, 0x00000000c0aec408,
0x00000000d1110000)
from space 34944K, 0% used [0x00000000d1110000, 0x00000000d1110000,
0x00000000d3330000)
to space 34944K, 0% used [0x00000000d3330000, 0x00000000d3330000,
0x00000000d5550000)
tenured generation total 699072K, used 0K [0x00000000d5550000,
0x0000000100000000, 0x0000000100000000)
the space 699072K, 0% used [0x00000000d5550000, 0x00000000d5550000,
0x00000000d5550200, 0x0000000100000000)
Metaspace used 2525K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 269K, capacity 386K, committed 512K, reserved 1048576K

#以下计算结果和max一样,说明Metaspace逻辑存在,但物理上并不属于heap空间
[root@centos8 ~]#echo '(314560+699072)*1024'|bc
1037959168

[root@centos8 ~]#cat HeapOom2.java
import java. util. Random;
    public class HeapOom2 {
    public static void main(String[] args) {
    String str = "I am ayaka";
    while (true){
        str += str + new Random().nextInt(88888888); //生成0到88888888之间的随机数字
        }
    }
}

[root@centos8 ~]#javac -cp . HeapOom2.java


[root@centos8 ~]#java -Xms100m -Xmx100m -XX:+PrintGCDetails -cp . HeapOom2
[GC (Allocation Failure) [DefNew: 27213K->2940K(30720K), 0.0026366 secs] 27213K-
>5624K(99008K), 0.0027124 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 24949K->0K(30720K), 0.0044922 secs] 27633K-
>8307K(99008K), 0.0045959 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[GC (Allocation Failure) [DefNew: 16550K->0K(30720K), 0.0037276 secs] 24857K-
>19041K(99008K), 0.0037898 secs] [Times: user=0.00 sys=0.01, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 21468K->0K(30720K), 0.0111687 secs] 40509K-
>40509K(99008K), 0.0112437 secs] [Times: user=0.00 sys=0.01, real=0.01 secs]
[GC (Allocation Failure) [DefNew: 21951K->0K(30720K), 0.0084048 secs] 62460K-
>61977K(99008K), 0.0084641 secs] [Times: user=0.00 sys=0.01, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 21468K->21468K(30720K), 0.0000177 secs]
[Tenured: 61977K->35141K(68288K), 0.0068683 secs] 83445K->35141K(99008K),
[Metaspace: 2479K->2479K(1056768K)], 0.0069358 secs] [Times: user=0.01 sys=0.00,
real=0.01 secs]
[Full GC (Allocation Failure) [Tenured: 35141K->32444K(68288K), 0.0091498 secs]
35141K->32444K(99008K), [Metaspace: 2479K->2479K(1056768K)], 0.0091975 secs]
[Times: user=0.01 sys=0.00, real=0.01 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3332)
at
java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.jav
a:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:674)
at java.lang.StringBuilder.append(StringBuilder.java:208)
at HeapOom2.main(HeapOom2.java:6)
Heap
def new generation total 30720K, used 1048K [0x00000000f9c00000,
0x00000000fbd50000, 0x00000000fbd50000)
eden space 27328K, 3% used [0x00000000f9c00000, 0x00000000f9d06158,
0x00000000fb6b0000)
from space 3392K, 0% used [0x00000000fba00000, 0x00000000fba00000,
0x00000000fbd50000)
to space 3392K, 0% used [0x00000000fb6b0000, 0x00000000fb6b0000,
0x00000000fba00000)
tenured generation total 68288K, used 32444K [0x00000000fbd50000,
0x0000000100000000, 0x0000000100000000)
the space 68288K, 47% used [0x00000000fbd50000, 0x00000000fdcff248,
0x00000000fdcff400, 0x0000000100000000)
Metaspace used 2510K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 268K, capacity 386K, committed 512K, reserved 1048576K

#java -cp . -Xms512m -Xmx1g HelloWorld

#测试用java程序
javac HelloWorld.java
java -classpath . -Xms512m -Xmx1g HelloWorld

[root@tomcat ~]#cat HelloWorld.java
public class HelloWorld extends Thread {
    public static void main(String[] args) {
        try {
        	while (true) {
                    Thread.sleep(2000);
                    System.out.println("hello ayaka);
        	}
        } catch (InterruptedException e) {
        	e.printStackTrace();
        }
    }
}

#编译为字节码.class文件
[root@tomcat ~]#javac HelloWorld.java
[root@tomcat ~]#ll HelloWorld.class
-rw-r--r-- 1 root root 590 Jul 13 16:31 HelloWorld.class
[root@tomcat ~]#file HelloWorld.class
HelloWorld.class: compiled Java class data, version 52.0 (Java 1.8)

#指定路径运行class文件
[root@tomcat ~]#java -cp . -Xms512m -Xmx1g HelloWorld
hello ayaka
hello ayaka
hello ayaka

#或者用下面方法指定CLASS文件的搜索路径
[root@tomcat ~]#echo $CLASSPATH
/usr/local/jdk/lib/:/usr/local/jdk/jre/lib/
[root@tomcat ~]#mv HelloWorld.class /usr/local/jdk/lib/

#分别执行多次观察
[root@tomcat ~]#java HelloWorld
[root@tomcat ~]#java -Xms256m -Xmx512m HelloWorld
[root@tomcat ~]#java -Xms128m -Xmx512m -XX:NewSize=64m -XX:MaxNewSize=200m
HelloWorld
hello ayaka

[root@tomcat ~]#jps
21299 Main
21418 Jps
21407 HelloWorld

#将Linux的图形工具显示到windows桌面
#方法1
#注意:先在windows上开启Xwindows Server，如Xmanager
[root@tomcat ~]#export DISPLAY=10.0.0.1:0.0
#方法2:使用 MobaXterm 连接
[root@tomcat ~]#yum -y install xorg-x11-xauth xorg-x11-fonts-* xorg-x11-font-utils xorg-x11-fonts-Type1

#运行图形工具
[roottomcat ~]#which jvisualvm
/usr/local/jdk/bin/jvisualvm
[root@tomcat ~]#jvisualvm

[root@centos8 ~]#cat HeapOom.java
import java.util.ArrayList;
import java.util.List;

public class HeapOom {
    public static void main(String[] args) {
        List<byte[]> list =new ArrayList<byte[]>();
        int i = 0;
        boolean flag = true;
        while(flag){
            try{
                i++;
                list.add(new byte[1024* 1024]);//每次增加一个1M大小的数组对象
                Thread.sleep(1000);
            }catch(Throwable e){
                e.printStackTrace();
                flag =false;
                System.out.println("count="+i);//记录运行的次数
            }
        }
    }
}

[root@centos8 ~]#java -Xms100m -Xmx200m HeapOom

[root@centos8 ~]#java HeapOom
java.lang.OutOfMemoryError: Java heap space
at HeapOom.main(HeapOom.java:12)
count=229

#安装OpenJDK
[root@centos8 ~]#dnf -y install java-1.8.0-openjdk-devel

[root@centos8 ~]#cat HeapOom.java
import java.util.ArrayList;
import java.util.List;

public class HeapOom {
    public static void main(String[] args) {
        List<byte[]> list =new ArrayList<byte[]>();
        int i = 0;
        boolean flag = true;
        while(flag){
            try{
                i++;
                list.add(new byte[1024* 1024]);//每次增加一个1M大小的数组对象
                Thread.sleep(1000);
            }catch(Throwable e){
                e.printStackTrace();
                flag =false;
                System.out.println("count="+i);//记录运行的次数
            }
        }
    }
}

[root@centos8 ~]#javac HeapOom.java
[root@centos8 ~]#java -cp . -Xms5m -Xmx10m -XX:+HeapDumpOnOutOfMemoryError HeapOom
java.lang.OutOfMemoryError: Java heap space
Dumping heap to java_pid96271.hprof ...
Heap dump file created [8134070 bytes in 0.031 secs]
java.lang.OutOfMemoryError: Java heap space
at HeapOom.main(HeapOom.java:12)
count=8

[root@centos8 ~]#cat HeapOom2.java
import java. util. Random;
public class HeapOom2 {
    public static void main(String[] args) {
        String str = "I am lao wang";
        while (true){
        str += str + new Random().nextInt(88888888);
        }
    }
}

[root@centos8 ~]#javac HeapOom2.java
[root@centos8 ~]#java -cp . -Xms5m -Xmx10m -XX:+HeapDumpOnOutOfMemoryError HeapOom2
java.lang.OutOfMemoryError: Java heap space
Dumping heap to java_pid96339.hprof ...
Heap dump file created [4925877 bytes in 0.016 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3332)
at
java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.jav
a:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:674)
at java.lang.StringBuilder.append(StringBuilder.java:208)
at HeapOom2.main(HeapOom2.java:6)

......
# OS specific support. $var _must_ be set to either true or false.
#添加下面一行
JAVA_OPTS="-server -Xms128m -Xmx512m -XX:NewSize=48m -XX:MaxNewSize=200m"

cygwin=false
darwin=false
........

-server：VM运行在server模式，为在服务器端最大化程序运行速度而优化
-client：VM运行在Client模式，为客户端环境减少启动时间而优化

[root@tomcat ~]#ps aux|grep tomcat
tomcat 22194 5.1 15.1 2497008 123480 ? Sl 13:31 0:03
/usr/local/jdk/jre/bin/java -
Djava.util.logging.config.file=/usr/local/tomcat/conf/logging.properties -
Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -server -
Xmx512m -Xms128m -XX:NewSize=48m -XX:MaxNewSize=200m -
Djdk.tls.ephemeralDHKeySize=2048 -
Djava.protocol.handler.pkgs=org.apache.catalina.webresources -
Dorg.apache.catalina.security.SecurityListener.UMASK=0027 -
Dignore.endorsed.dirs= -classpath
/usr/local/tomcat/bin/bootstrap.jar:/usr/local/tomcat/bin/tomcat-juli.jar -
Dcatalina.base=/usr/local/tomcat -Dcatalina.home=/usr/local/tomcat -
Djava.io.tmpdir=/usr/local/tomcat/temp org.apache.catalina.startup.Bootstrap
start

-XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=80 -XX:+UseCMSCompactAtFullCollection -XX:CMSFullGCsBeforeCompaction=5

[root@ubuntu2204 ~]#java -version
java version "11.0.17" 2022-10-18 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.17+10-LTS-269)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.17+10-LTS-269, mixed mode)
[root@ubuntu2204 ~]#java -XX:+PrintCommandLineFlags 2> /dev/null
-XX:G1ConcRefinementThreads=2 -XX:GCDrainStackTargetSize=64 -XX:InitialHeapSize=31811840 -XX:MaxHeapSize=508989440 -XX:+PrintCommandLineFlags
-XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC

[root@ubuntu2204 ~]#java -version
java version "1.8.0_351"
Java(TM) SE Runtime Environment (build 1.8.0_351-b10)
Java HotSpot(TM) 64-Bit Server VM (build 25.351-b10, mixed mode)
[root@ubuntu2204 ~]#java -XX:+PrintCommandLineFlags 2> /dev/null
-XX:InitialHeapSize=31811904 -XX:MaxHeapSize=508990464 -
XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops
-XX:+UseParallelGC

#Linux
[root@rocky8 ~]#java -XX:+PrintCommandLineFlags -version
-XX:InitialHeapSize=31964352 -XX:MaxHeapSize=511429632 -
XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops
-XX:+UseParallelGC
java version "1.8.0_301"
Java(TM) SE Runtime Environment (build 1.8.0_301-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.301-b09, mixed mode)

#Windows
C:\Users\wang>java -XX:+PrintCommandLineFlags -version
-XX:InitialHeapSize=1071317952 -XX:MaxHeapSize=17141087232 -
XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops
-XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
java version "1.8.0_281"
Java(TM) SE Runtime Environment (build 1.8.0_281-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.281-b09, mixed mode)

#-XX:+UseSerialGC表示Serial+SerialOld
[root@rocky8 ~]#java -Xms10m -Xmx10m -XX:+PrintGCDetails -XX:+UseSerialGC -cp . HeapOom2
[GC (Allocation Failure) [DefNew: 2376K->320K(3072K), 0.0004583 secs] 2376K-
>657K(9920K), 0.0004984 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 2374K->0K(3072K), 0.0003771 secs] 2711K-
>1257K(9920K), 0.0003866 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 2447K->0K(3072K), 0.0004045 secs] 3704K-
>2857K(9920K), 0.0004243 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 1643K->0K(3072K), 0.0001604 secs] 4500K-
>4457K(9920K), 0.0001758 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 1600K->0K(3072K), 0.0002896 secs][Tenured:
6057K->2856K(6848K), 0.0009171 secs] 6057K->2856K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0012276 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 1647K->1647K(3072K), 0.0000053 secs][Tenured:
6056K->2056K(6848K), 0.0006369 secs] 7703K->2056K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0006801 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[GC (Allocation Failure) [DefNew: 1600K->1600K(3072K), 0.0000057 secs][Tenured:
5256K->5256K(6848K), 0.0005282 secs] 6856K->5256K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0005636 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [Tenured: 5256K->5042K(6848K), 0.0008440 secs]
5256K->5042K(9920K), [Metaspace: 2480K->2480K(1056768K)], 0.0008589 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3332)
at
java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.jav
a:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:674)
at java.lang.StringBuilder.append(StringBuilder.java:208)
at HeapOom2.main(HeapOom2.java:6)
Heap
def new generation total 3072K, used 105K [0x00000000ff600000,
0x00000000ff950000, 0x00000000ff950000)
eden space 2752K, 3% used [0x00000000ff600000, 0x00000000ff61a5c8,
0x00000000ff8b0000)
from space 320K, 0% used [0x00000000ff900000, 0x00000000ff900000,
0x00000000ff950000)
to space 320K, 0% used [0x00000000ff8b0000, 0x00000000ff8b0000,
0x00000000ff900000)
tenured generation total 6848K, used 5042K [0x00000000ff950000,
0x0000000100000000, 0x0000000100000000)
the space 6848K, 73% used [0x00000000ff950000, 0x00000000ffe3cac8,
0x00000000ffe3cc00, 0x0000000100000000)
Metaspace used 2514K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 268K, capacity 386K, committed 512K, reserved 1048576K

#-XX:+UseParNewGC表示ParNew+SerialOld
[root@rocky8 ~]#java -Xms10m -Xmx10m -XX:+PrintGCDetails -XX:+UseParNewGC -cp . HeapOom2
Java HotSpot(TM) 64-Bit Server VM warning: Using the ParNew young collector with
the Serial old collector is deprecated and will likely be removed in a future
release
[GC (Allocation Failure) [ParNew: 2373K->265K(3072K), 0.0008588 secs] 2373K-
>664K(9920K), 0.0008885 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[GC (Allocation Failure) [ParNew: 2316K->99K(3072K), 0.0007617 secs] 2716K-
>1559K(9920K), 0.0007802 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 2543K->24K(3072K), 0.0006585 secs] 4002K-
>3082K(9920K), 0.0006758 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1665K->6K(3072K), 0.0004363 secs] 4722K-
>4660K(9920K), 0.0004525 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1603K->2K(3072K), 0.0005977 secs][Tenured:
6252K->2652K(6848K), 0.0009806 secs] 6258K->2652K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0015996 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1645K->1645K(3072K), 0.0000045 secs][Tenured:
5847K->1853K(6848K), 0.0006388 secs] 7492K->1853K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0006629 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1597K->0K(3072K), 0.0004854 secs][Tenured:
5048K->5048K(6848K), 0.0006832 secs] 6646K->5048K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0011950 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [Tenured: 5048K->5035K(6848K), 0.0006889 secs]
5048K->5035K(9920K), [Metaspace: 2480K->2480K(1056768K)], 0.0007030 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3332)
at
java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.jav
a:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:674)
at java.lang.StringBuilder.append(StringBuilder.java:208)
at HeapOom2.main(HeapOom2.java:6)
Heap
par new generation total 3072K, used 105K [0x00000000ff600000,
0x00000000ff950000, 0x00000000ff950000)
eden space 2752K, 3% used [0x00000000ff600000, 0x00000000ff61a5c8,
0x00000000ff8b0000)
from space 320K, 0% used [0x00000000ff8b0000, 0x00000000ff8b0000,
0x00000000ff900000)
to space 320K, 0% used [0x00000000ff900000, 0x00000000ff900000,
0x00000000ff950000)
tenured generation total 6848K, used 5035K [0x00000000ff950000,
0x0000000100000000, 0x0000000100000000)
the space 6848K, 73% used [0x00000000ff950000, 0x00000000ffe3af00,
0x00000000ffe3b000, 0x0000000100000000)
Metaspace used 2514K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 268K, capacity 386K, committed 512K, reserved 1048576K


#-XX:+UseParallelGC表示PS+ParOld 此为默认值
[root@rocky8 ~]#java -Xms10m -Xmx10m -XX:+PrintGCDetails -XX:+UseParallelGC -cp . HeapOom2
[GC (Allocation Failure) [PSYoungGen: 1953K->491K(2560K)] 1953K->755K(9728K),
0.0009754 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 2512K->492K(2560K)] 2775K->755K(9728K),
0.0005462 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 2512K->96K(2560K)] 4359K->2735K(9728K),
0.0006484 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 888K->96K(2560K)] 5111K->4319K(9728K),
0.0004700 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 96K->96K(2560K)] 4319K->4319K(9728K),
0.0004402 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [PSYoungGen: 96K->0K(2560K)] [ParOldGen: 4223K-
>2632K(7168K)] 4319K->2632K(9728K), [Metaspace: 2480K->2480K(1056768K)],
0.0020238 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) --[PSYoungGen: 1624K->1624K(2560K)] 7424K-
>7424K(9728K), 0.0004027 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Ergonomics) [PSYoungGen: 1624K->0K(2560K)] [ParOldGen: 5800K-
>1839K(7168K)] 7424K->1839K(9728K), [Metaspace: 2480K->2480K(1056768K)],
0.0018894 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[GC (Allocation Failure) [PSYoungGen: 1584K->0K(1536K)] 6591K->5007K(8704K),
0.0004222 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] 5007K->5007K(9216K),
0.0003842 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] [ParOldGen: 5007K-
>5007K(7168K)] 5007K->5007K(9216K), [Metaspace: 2480K->2480K(1056768K)],
0.0016387 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] 5007K->5007K(9216K),
0.0003614 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] [ParOldGen: 5007K-
>4994K(7168K)] 5007K->4994K(9216K), [Metaspace: 2480K->2480K(1056768K)],
0.0017426 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3332)
at
java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.jav
a:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:674)
at java.lang.StringBuilder.append(StringBuilder.java:208)
at HeapOom2.main(HeapOom2.java:6)
Heap
PSYoungGen total 2048K, used 41K [0x00000000ffd00000, 0x0000000100000000,
0x0000000100000000)
eden space 1024K, 4% used
[0x00000000ffd00000,0x00000000ffd0a518,0x00000000ffe00000)
from space 1024K, 0% used
[0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
to space 1024K, 0% used
[0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
ParOldGen total 7168K, used 4994K [0x00000000ff600000, 0x00000000ffd00000,
0x00000000ffd00000)
object space 7168K, 69% used
[0x00000000ff600000,0x00000000ffae0a98,0x00000000ffd00000)
Metaspace used 2514K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 268K, capacity 386K, committed 512K, reserved 1048576K
#-XX:+UseParallelOldGC表示PS+ParOld
[root@rocky8 ~]#java -Xms10m -Xmx10m -XX:+PrintGCDetails -XX:+UseParallelOldGC
-cp . HeapOom2
[GC (Allocation Failure) [PSYoungGen: 1933K->486K(2560K)] 1933K->748K(9728K),
0.0009954 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 2482K->486K(2560K)] 2744K->748K(9728K),
0.0005175 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 2482K->96K(2560K)] 4308K->2703K(9728K),
0.0006469 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 878K->96K(2560K)] 5049K->4267K(9728K),
0.0005057 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 96K->96K(2560K)] 4267K->4267K(9728K),
0.0004297 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [PSYoungGen: 96K->0K(2560K)] [ParOldGen: 4171K-
>2602K(7168K)] 4267K->2602K(9728K), [Metaspace: 2480K->2480K(1056768K)],
0.0020167 secs] [Times: user=0.00 sys=0.01, real=0.00 secs]
[GC (Allocation Failure) --[PSYoungGen: 1604K->1604K(2560K)] 7334K-
>7334K(9728K), 0.0004226 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Ergonomics) [PSYoungGen: 1604K->0K(2560K)] [ParOldGen: 5729K-
>1819K(7168K)] 7334K->1819K(9728K), [Metaspace: 2480K->2480K(1056768K)],
0.0018280 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[GC (Allocation Failure) [PSYoungGen: 1563K->0K(1536K)] 6511K->4947K(8704K),
0.0004604 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] 4947K->4947K(9216K),
0.0003834 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] [ParOldGen: 4947K-
>4947K(7168K)] 4947K->4947K(9216K), [Metaspace: 2480K->2480K(1056768K)],
0.0012999 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] 4947K->4947K(9216K),
0.0003402 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [PSYoungGen: 0K->0K(2048K)] [ParOldGen: 4947K-
>4934K(7168K)] 4947K->4934K(9216K), [Metaspace: 2480K->2480K(1056768K)],
0.0018222 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3332)
at
java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.jav
a:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:674)
at java.lang.StringBuilder.append(StringBuilder.java:208)
at HeapOom2.main(HeapOom2.java:6)
Heap
PSYoungGen total 2048K, used 41K [0x00000000ffd00000, 0x0000000100000000,
0x0000000100000000)
eden space 1024K, 4% used
[0x00000000ffd00000,0x00000000ffd0a518,0x00000000ffe00000)
from space 1024K, 0% used
[0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
to space 1024K, 0% used
[0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
ParOldGen total 7168K, used 4934K [0x00000000ff600000, 0x00000000ffd00000,
0x00000000ffd00000)
object space 7168K, 68% used
[0x00000000ff600000,0x00000000ffad1a08,0x00000000ffd00000)
Metaspace used 2514K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 268K, capacity 386K, committed 512K, reserved 1048576K

#-XX:+UseConcMarkSweepGC表示ParNew+CMS
[root@rocky8 ~]#java -Xms10m -Xmx10m -XX:+PrintGCDetails -XX:+UseConcMarkSweepGC -cp . HeapOom2
[GC (Allocation Failure) [ParNew: 2365K->273K(3072K), 0.0004709 secs] 2365K-
>674K(9920K), 0.0005774 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 2324K->100K(3072K), 0.0008058 secs] 2726K-
>1563K(9920K), 0.0008263 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 2543K->25K(3072K), 0.0004260 secs] 4006K-
>3085K(9920K), 0.0004505 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1665K->6K(3072K), 0.0004862 secs] 4726K-
>4664K(9920K), 0.0005126 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (CMS Initial Mark) [1 CMS-initial-mark: 4657K(6848K)] 6261K(9920K),
0.0001252 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[CMS-concurrent-mark-start]
[CMS-concurrent-mark: 0.000/0.000 secs] [Times: user=0.00 sys=0.00, real=0.00
secs]
[CMS-concurrent-preclean-start]
[CMS-concurrent-preclean: 0.000/0.000 secs] [Times: user=0.00 sys=0.00,
real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1603K->2K(3072K), 0.0005197 secs][CMS
(concurrent mode failure): 6255K->2655K(6848K), 0.0010552 secs] 6261K-
>2655K(9920K), [Metaspace: 2480K->2480K(1056768K)], 0.0016009 secs] [Times:
user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1644K->1644K(3072K), 0.0000147 secs][CMS:
5850K->1857K(6848K), 0.0007565 secs] 7495K->1857K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0007937 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [ParNew: 1597K->0K(3072K), 0.0001449 secs][CMS: 5052K-
>5052K(6848K), 0.0007624 secs] 6649K->5052K(9920K), [Metaspace: 2480K-
>2480K(1056768K)], 0.0009314 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (Allocation Failure) [CMS: 5052K->5039K(6848K), 0.0007938 secs] 5052K-
>5039K(9920K), [Metaspace: 2480K->2480K(1056768K)], 0.0008031 secs] [Times:
user=0.00 sys=0.00, real=0.00 secs]
[GC (CMS Initial Mark) [1 CMS-initial-mark: 5039K(6848K)] 5039K(9920K),
0.0001806 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[CMS-concurrent-mark-start]
[CMS-concurrent-mark: 0.000/0.000 secs] [Times: user=0.00 sys=0.00, real=0.00
secs]
[CMS-concurrent-preclean-start]
[CMS-concurrent-preclean: 0.000/0.000 secs] [Times: user=0.00 sys=0.00,
real=0.00 secs]
[GC (CMS Final Remark) [YG occupancy: 50 K (3072 K)][Rescan (parallel) ,
0.0001153 secs][weak refs processing, 0.0000026 secs][class unloading, 0.0000639
secs][scrub symbol table, 0.0001370 secs][scrub string table, 0.0000589 secs][1
CMS-remark: 5039K(6848K)] 5089K(9920K), 0.0004434 secs] [Times: user=0.00
sys=0.00, real=0.00 secs]
[CMS-concurrent-sweep-start]
[CMS-concurrent-sweep: 0.000/0.000 secs] [Times: user=0.00 sys=0.00, real=0.00
secs]
[CMS-concurrent-reset-start]
[CMS-concurrent-reset: 0.000/0.000 secs] [Times: user=0.00 sys=0.00, real=0.00
secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3332)
at
java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.jav
a:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:674)
at java.lang.StringBuilder.append(StringBuilder.java:208)
at HeapOom2.main(HeapOom2.java:6)
Heap
par new generation total 3072K, used 105K [0x00000000ff600000,
0x00000000ff950000, 0x00000000ff950000)
eden space 2752K, 3% used [0x00000000ff600000, 0x00000000ff61a5e0,
0x00000000ff8b0000)
from space 320K, 0% used [0x00000000ff8b0000, 0x00000000ff8b0000,
0x00000000ff900000)
to space 320K, 0% used [0x00000000ff900000, 0x00000000ff900000,
0x00000000ff950000)
concurrent mark-sweep generation total 6848K, used 245K [0x00000000ff950000,
0x0000000100000000, 0x0000000100000000)
Metaspace used 2514K, capacity 4486K, committed 4864K, reserved 1056768K
class space used 268K, capacity 386K, committed 512K, reserved 1048576K

[root@centos8 ~]#java |& grep '-server'
-server to select the "server" VM
The default VM is server.
[root@centos8 ~]#tail -n 2 /usr/local/jdk/jre/lib/amd64/jvm.cfg
-server KNOWN
-client IGNORE

#将参数加入到bin/catalina.sh中，重启观察Tomcat status。老年代已经使用CMS
[root@tomcat ~]#vim /usr/local/tomcat/bin/catalina.sh
......
# OS specific support. $var _must_ be set to either true or false.
JAVA_OPTS="-server -Xmx512m -Xms128m -XX:NewSize=48m -XX:MaxNewSize=200m -XX:+UseConcMarkSweepGC -XX:+UseCMSCompactAtFullCollection -XX:CMSFullGCsBeforeCompaction=5"

cygwin=false
darwin=false
os400=false

.......
[root@tomcat ~]#systemctl restart tomcat
[root@tomcat ~]#ps aux |grep tomcat
tomcat 22093 2.2 15.2 3018616 148448 ? Sl 17:51 0:06
/usr/local/jdk/bin/java -
Djava.util.logging.config.file=/usr/local/tomcat/conf/logging.properties -
Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -server -
Xmx512m -Xms128m -XX:NewSize=48m -XX:MaxNewSize=200m -XX:+UseConcMarkSweepGC -
XX:+UseCMSCompactAtFullCollection -XX:CMSFullGCsBeforeCompaction=5 -
Djdk.tls.ephemeralDHKeySize=2048 -
Djava.protocol.handler.pkgs=org.apache.catalina.webresources -
Dorg.apache.catalina.security.SecurityListener.UMASK=0027 -
Dignore.endorsed.dirs= -classpath
/usr/local/tomcat/bin/bootstrap.jar:/usr/local/tomcat/bin/tomcat-juli.jar -
Dcatalina.base=/usr/local/tomcat -Dcatalina.home=/usr/local/tomcat -
Djava.io.tmpdir=/usr/local/tomcat/temp org.apache.catalina.startup.Bootstrap
start
root 22158 0.0 0.1 12108 1084 pts/1 S+ 17:56 0:00 grep --
color=auto tomcat

jps：Java virutal machine Process Status tool，
jps [-q] [-mlvV] [<hostid>]
-q：静默模式；
-v：显示传递给jvm的命令行参数；
-m：输出传入main方法的参数；
-l：输出main类或jar完全限定名称；
-v：显示通过flag文件传递给jvm的参数；
[<hostid>]：主机id，默认为localhost；

#显示java进程
[root@tomcat ~]#jps
22357 Jps
21560 Main
21407 HelloWorld

#详细列出当前Java进程信息
[root@tomcat ~]#jps -l -v
21560 org.netbeans.Main -Djdk.home=/usr/local/jdk -
Dnetbeans.default_userdir_root=/root/.visualvm -
Dnetbeans.dirs=/usr/local/jdk/lib/visualvm/visualvm:/usr/local/jdk/lib/visualvm/
profiler: -Dnetbeans.home=/usr/local/jdk/lib/visualvm/platform -Xms24m -Xmx256m
-Dsun.jvmstat.perdata.syncWaitMs=10000 -Dsun.java2d.noddraw=true -
Dsun.java2d.d3d=false -Dnetbeans.keyring.no.master=true -
Dplugin.manager.install.global=false --add-exports=java.desktop/sun.awt=ALL-
UNNAMED --add-exports=jdk.jvmstat/sun.jvmstat.monitor.event=ALL-UNNAMED --add-
exports=jdk.jvmstat/sun.jvmstat.monitor=ALL-UNNAMED --add-
exports=java.desktop/sun.swing=ALL-UNNAMED --add-
exports=jdk.attach/sun.tools.attach=ALL-UNNAMED --add-modules=java.activation -
XX:+IgnoreUnrecognizedVMOptions -XX:+HeapDumpOnOutOfMemoryError -
XX:HeapDumpPath=/root/.visualvm/8u131/var/log/heapdump.hprof
22270 sun.tools.jps.Jps -
Denv.class.path=/usr/local/jdk/lib/:/usr/local/jdk/jre/lib/ -
Dapplication.home=/usr/local/jdk1.8.0_241 -Xms8m
21407 HelloWorld -Xms256m -Xmx512m

jinfo [option] <pid>
-flags：打印 VM flags
-sysprops：to print Java system properties
-flag <name>：to print the value of the named VM flag

#先获得一个java进程ID，然后jinfo
[root@tomcat ~]#jps
22357 Jps
21560 Main
21407 HelloWorld
[root@tomcat ~]#jinfo 21407
Attaching to process ID 21407, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.241-b07
Java System Properties:
java.runtime.name = Java(TM) SE Runtime Environment
java.vm.version = 25.241-b07
sun.boot.library.path = /usr/local/jdk1.8.0_241/jre/lib/amd64
java.vendor.url = http://java.oracle.com/
java.vm.vendor = Oracle Corporation
path.separator = :
java.rmi.server.randomIDs = true
file.encoding.pkg = sun.io
java.vm.name = Java HotSpot(TM) 64-Bit Server VM
sun.os.patch.level = unknown
sun.java.launcher = SUN_STANDARD
user.country = US
user.dir = /data
java.vm.specification.name = Java Virtual Machine Specification
java.runtime.version = 1.8.0_241-b07
java.awt.graphicsenv = sun.awt.X11GraphicsEnvironment
os.arch = amd64
java.endorsed.dirs = /usr/local/jdk1.8.0_241/jre/lib/endorsed
java.io.tmpdir = /tmp
line.separator =
java.vm.specification.vendor = Oracle Corporation
os.name = Linux
sun.jnu.encoding = UTF-8
java.library.path = /usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib
java.specification.name = Java Platform API Specification
java.class.version = 52.0
sun.management.compiler = HotSpot 64-Bit Tiered Compilers
os.version = 4.18.0-147.el8.x86_64
user.home = /root
user.timezone = Asia/Shanghai
java.awt.printerjob = sun.print.PSPrinterJob
file.encoding = UTF-8
java.specification.version = 1.8
user.name = root
java.class.path = /usr/local/jdk/lib/:/usr/local/jdk/jre/lib/
java.vm.specification.version = 1.8
sun.arch.data.model = 64
sun.java.command = HelloWorld
java.home = /usr/local/jdk1.8.0_241/jre
user.language = en
java.specification.vendor = Oracle Corporation
awt.toolkit = sun.awt.X11.XToolkit
java.vm.info = mixed mode
java.version = 1.8.0_241
java.ext.dirs = /usr/local/jdk1.8.0_241/jre/lib/ext:/usr/java/packages/lib/ext
sun.boot.class.path =
/usr/local/jdk1.8.0_241/jre/lib/resources.jar:/usr/local/jdk1.8.0_241/jre/lib/rt
.jar:/usr/local/jdk1.8.0_241/jre/lib/sunrsasign.jar:/usr/local/jdk1.8.0_241/jre/
lib/jsse.jar:/usr/local/jdk1.8.0_241/jre/lib/jce.jar:/usr/local/jdk1.8.0_241/jre
/lib/charsets.jar:/usr/local/jdk1.8.0_241/jre/lib/jfr.jar:/usr/local/jdk1.8.0_24
1/jre/classes
java.vendor = Oracle Corporation
file.separator = /
java.vendor.url.bug = http://bugreport.sun.com/bugreport/
sun.io.unicode.encoding = UnicodeLittle
sun.cpu.endian = little
sun.cpu.isalist =
VM Flags:
Non-default VM flags: -XX:CICompilerCount=2 -XX:InitialHeapSize=268435456 -
XX:MaxHeapSize=536870912 -XX:MaxNewSize=178913280 -XX:MinHeapDeltaBytes=196608 -
XX:NewSize=89456640 -XX:OldSize=178978816 -XX:+UseCompressedClassPointers -
XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps
Command line: -Xms256m -Xmx512m

[root@tomcat ~]#jinfo -flags 21407
Attaching to process ID 21407, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.241-b07
Non-default VM flags: -XX:CICompilerCount=2 -XX:InitialHeapSize=268435456 -
XX:MaxHeapSize=536870912 -XX:MaxNewSize=178913280 -XX:MinHeapDeltaBytes=196608 -
XX:NewSize=89456640 -XX:OldSize=178978816 -XX:+UseCompressedClassPointers -
XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps
Command line: -Xms256m -Xmx512m

jstat -help|-options
jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
[<interval> [<count>]]
interval：时间间隔，单位是毫秒；
count：显示的次数；

#返回可用统计项列表
# jstat -options
-class：class loader
-compiler：JIT
-gc：gc
-gccapacity：统计堆中各代的容量
-gccause：
-gcmetacapacity
-gcnew：新生代
-gcnewcapacity
-gcold：老年代
-gcoldcapacity
-gcutil
-printcompilation

S0C: 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).
MC: Metaspace capacity (kB).
MU: Metacspace utilization (kB).
CCSC: Compressed class space capacity (kB).
CCSU: Compressed class space used (kB).
YGC: Number of young generation garbage collection events.
YGCT: Young generation garbage collection time.
FGC: Number of full GC events.
FGCT: Full garbage collection time.
GCT: Total garbage collection time.
TT: Tenuring threshold.
MTT: Maximum tenuring threshold.
DSS: Desired survivor size (kB)

[root@tomcat ~]#jstat -gc 21407
S0C S1C S0U S1U EC EU OC OU MC MU
CCSC CCSU YGC YGCT FGC FGCT GCT
8704.0 8704.0 1563.6 0.0 69952.0 58033.0 174784.0 0.0 9344.0
8830.0 1152.0 1013.0 2 0.050 0 0.000 0.050

S0C:S0区容量
YGC：新生代的垃圾回收次数
YGCT：新生代垃圾回收消耗的时长；
FGC：Full GC的次数
FGCT：Full GC消耗的时长
GCT：GC消耗的总时长

#3次，一秒一次
[root@tomcat ~]#jstat -gcnew 21407 1000 3
S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT
8704.0 8704.0 1563.6 0.0 15 15 4352.0 69952.0 62794.3 2 0.050
8704.0 8704.0 1563.6 0.0 15 15 4352.0 69952.0 62794.3 2 0.050
8704.0 8704.0 1563.6 0.0 15 15 4352.0 69952.0 63074.5 2 0.050

jstack [-l] <pid>
jstack -F [-m] [-l] <pid>
-l：long listings，会显示额外的锁信息，因此，发生死锁时常用此选项
-m：混合模式，既输出java堆栈信息，也输出C/C++堆栈信息
-F：当使用"jstack -l PID"无响应，可以使用-F强制输出信息

#先获得一个java进程PID，然后jinfo
[root@tomcat ~]#jstack -l 21407
2020-02-15 13:49:56
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.241-b07 mixed mode):
"RMI TCP Connection(4)-10.0.0.101" #16 daemon prio=9 os_prio=0
tid=0x00007f279c29e800 nid=0x5753 runnable [0x00007f279b181000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
......

#查看进程堆内存情况
[root@tomcat ~]#jmap -heap 21407
Attaching to process ID 21407, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.241-b07

using thread-local object allocation.
Mark Sweep Compact GC
Heap Configuration:
MinHeapFreeRatio = 40
MaxHeapFreeRatio = 70
MaxHeapSize = 536870912 (512.0MB)
NewSize = 89456640 (85.3125MB)
MaxNewSize = 178913280 (170.625MB)
OldSize = 178978816 (170.6875MB)
NewRatio = 2
SurvivorRatio = 8
MetaspaceSize = 21807104 (20.796875MB)
CompressedClassSpaceSize = 1073741824 (1024.0MB)
MaxMetaspaceSize = 17592186044415 MB
G1HeapRegionSize = 0 (0.0MB)
Heap Usage:
New Generation (Eden + 1 Survivor Space):
capacity = 80543744 (76.8125MB)
used = 4893096 (4.666419982910156MB)
free = 75650648 (72.14608001708984MB)
6.075078903707283% used
Eden Space:
capacity = 71630848 (68.3125MB)
used = 3301800 (3.1488418579101562MB)
free = 68329048 (65.16365814208984MB)
4.609466580655306% used
From Space:
capacity = 8912896 (8.5MB)
used = 1591296 (1.517578125MB)
free = 7321600 (6.982421875MB)
17.85386029411765% used
To Space:
capacity = 8912896 (8.5MB)
used = 0 (0.0MB)
free = 8912896 (8.5MB)
0.0% used
tenured generation:
capacity = 178978816 (170.6875MB)
used = 0 (0.0MB)
free = 178978816 (170.6875MB)
0.0% used
4926 interned Strings occupying 389832 bytes.

jmap [option] <pid>
#查看堆空间的详细信息：
jmap -heap <pid>

[root@t1 ~]#jmap -heap 96334
Attaching to process ID 96334, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.251-b08
using thread-local object allocation.
Mark Sweep Compact GC
Heap Configuration:
MinHeapFreeRatio = 40
MaxHeapFreeRatio = 70
MaxHeapSize = 251658240 (240.0MB)
NewSize = 5570560 (5.3125MB)
MaxNewSize = 83886080 (80.0MB)
OldSize = 11206656 (10.6875MB)

#查看堆内存中的对象的数目：
jmap -histo[:live] <pid>
		live：只统计活动对象；
	
#保存堆内存数据至文件中，而后使用jvisualvm或jhat进行查看：
jmap -dump:<dump-options> <pid>
dump-options:
live dump only live objects; if not specified, all objects in the heap are

dumped.
format=b binary format
file=<file> dump heap to <file>

#为Java程序开启JMX很简单，只要在运行Java程序的命令后面指定如下命令即可
java \
-Dcom.sun.management.jmxremote \ #启用远程监控JMX
-Djava.rmi.server.hostname=10.0.0.100 \ #指定自已监听的主机的IP，不支持0.0.0.0
-Dcom.sun.management.jmxremote.port=12345 \ #指定监听的PORT
-Dcom.sun.management.jmxremote.authenticate=false \
-Dcom.sun.management.jmxremote.ssl=false \
-jar app.jar|app.war

vim /usr/local/tomcat/bin/catalina.sh
CATALINA_OPTS="$CATALINA_OPTS
-Dcom.sun.management.jmxremote #启用远程监控JMX
-Dcom.sun.management.jmxremote.port=XXXXX #默认启动的JMX端口号，要和zabbix添加主机时候的端口一致即可
-Dcom.sun.management.jmxremote.authenticate=false #不使用用户名密码
-Dcom.sun.management.jmxremote.ss1=false #不使用ssl认证
-Djava.rmi.server.hostname=<JAVA主机IP>" #tomcat主机自己的IP地址,不要写zabbix服务器的地址

[root@tomcat ~]#vim /usr/local/tomcat/bin/catalina.sh
.......
# -----------------------------------------------------------------------------
CATALINA_OPTS="$CATALINA__OPTS \
-Dcom.sun.management.jmxremote \
-Djava.rmi.server.hostname=10.0.0.101 \
-Dcom.sun.management.jmxremote.port=12345 \
-Dcom.sun.management.jmxremote.authenticate=false \
-Dcom.sun.management.jmxremote.ssl=false"

# OS specific support. $var _must_ be set to either true or false.
.......
[root@tomcat ~]#systemctl restart tomcat
[root@tomcat ~]#ss -ntl
State Recv-Q Send-Q Local Address:Port Peer
Address:Port
LISTEN 0 128 0.0.0.0:22
0.0.0.0:*
LISTEN 0 100 127.0.0.1:25
0.0.0.0:*
LISTEN 0 128 [::]:22
[::]:*
LISTEN 0 50 *:12345
*:*
LISTEN 0 100 [::1]:25
[::]:*
LISTEN 0 50 *:38563
*:*
LISTEN 0 1 [::ffff:127.0.0.1]:8005
*:*
LISTEN 0 50 *:40613
*:*
LISTEN 0 100 *:8080
*:*

JAVA_OPTS="-server -Xms4g -Xmx4g -XX:NewSize= -XX:MaxNewSize= "

-server：服务器模式
-Xms：堆内存初始化大小
-Xmx：堆内存空间上限
-XX:NewSize=：新生代空间初始化大小
-XX:MaxNewSize=：新生代空间最大值

[root@centos8 ~]#vim /usr/local/tomcat/bin/catalina.sh
JAVA_OPTS="-server -Xms4g -Xmx4g -Xss512k -Xmn1g -XX:CMSInitiatingOccupancyFraction=65 -XX:+AggressiveOpts -XX:+UseBiasedLocking -XX:+DisableExplicitGC -XX:MaxTenuringThreshold=10 -XX:NewRatio=2 -XX:PermSize=128m -XX:MaxPermSize=512m -XX:CMSFullGCsBeforeCompaction=5 -XX:+ExplicitGCInvokesConcurrent -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:+CMSParallelRemarkEnabled -XX:+UseCMSCompactAtFullCollection -XX:LargePageSizeInBytes=128m -XX:+UseFastAccessorMethods"
#一台tomcat服务器并发连接数不高,生产建议分配物理内存通常4G到8G较多,如果需要更多连接,一般会利用虚拟化技术实现多台tomcat

[root@centos8 ~]#vim /usr/local/tomcat/conf/server.xml
......
<Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" maxThreads="2000"/>
......