一、JVM的参数类型
1.Boolean类型
格式：-XX:[+-]<name>表示启用或者禁用name属性。
比如：-XX:+UseConcMarkSweepGC
-XX:+UseG1GC
2.非Boolean类型
格式：-XX:<name>=<value>表示name属性的值是value。
比如：-XX:MaxGCPauseMillis=500
XX:GCTimeRatio=19
3.-Xmx -Xms(虚拟机所在的最大、最小内存)
不是X参数，而是XX参数
-Xms等价于-XX:InitialHeapSize
-Xmx等价于-XX:MaxHeapSize
jinfo -flag MaxHeapSize <PID>
线程大小（单位：kb）：jinfo -flag ThreadStackSize <PID>
4.查看初始值：-XX:+PrintFlagsInitial
5.查看修改值：-XX:+PrintFlagsFinal
1.终端输入：java -XX:+PrintFlagsFinal -version > flags.txt
6.查看tomcat的最大内存是设置了多少：
jinfo -flag MaxHeapSize <Pid>
7.查看tomcat已经被我们手动赋过的值：
jinfo -flag <Pid>
8.查看垃圾回收器：
二、jstat查看JVM统计信息
可以查看类装载、垃圾收集、JIT编译
1.查看类加载的情况：
jstat -class <PID>
2.查看垃圾回收的情况：
每隔1秒钟输出10次
jstat -gc <PID> 1000 10
非堆区是操作系统的本地内存
三、jmap+MAT内存溢出
1.保存为java镜像文件：
jmap -dump:format=b,file=heap.hprof <Pid>
四、jstack与线程状态
1.查看进程的资源占用率
top -p <pid> -H
2.用jstack查看线程情况
jstack <pid> > test.txt
3.Linux下把十进制转16进制,在test.txt中要使用
printf "%x" <pid>
用十六进制数在导出的txt中搜索，这样就能找到对应的类。
参考文档
第一章
无
第二章
jdk8工具集
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/index.html
Troubleshooting
https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/
jps
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jps.html
jinfo
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jinfo.html
jstat
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstat.html
jmap：
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jmap.html
mat:
http://www.eclipse.org/mat/downloads.php
jstack：
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstack.html
java线程的状态
https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr034.html
java线程状态转化：
https://mp.weixin.qq.com/s/GsxeFM7QWuR--Kbpb7At2w
死循环导致CPU负载高
https://blog.csdn.net/goldenfish1919/article/details/8755378
正则表达式导致死循环：
https://blog.csdn.net/goldenfish1919/article/details/49123787
第三章
jvisualVM：
https://docs.oracle.com/javase/8/docs/technotes/guides/visualvm/index.html
https://visualvm.github.io/documentation.html
jvisulaVM如何添加插件
https://visualvm.github.io/index.html
第四章
btrace下载
https://github.com/btraceio/btrace
https://github.com/btraceio/btrace/releases/tag/v1.3.11
第五章
jdwp协议：
https://www.ibm.com/developerworks/cn/java/j-lo-jpda3/
tomcat-manager：
{tomcat}/webapps/docs/manager-howto.html
psi-probe:
https://github.com/psi-probe/psi-probe
tomcat优化相关参数：
${tomcat}/webapps/docs/config/http.html
${tomcat}/webapps/docs/config/host.html
${tomcat}/webapps/docs/config/context.html
${tomcat}/webapps/docs/connectors.html
apr连接器：
http://apr.apache.org/
第六章
nginx官网文档
http://nginx.org/en/docs/
nginx安装：
http://nginx.org/en/linux_packages.html
ngx_http_stub_status：
http://nginx.org/en/docs/http/ngx_http_stub_status_module.html
ngxtop：
https://github.com/lebinh/ngxtop
nginx-rdd
http://www.linuxde.net/2012/04/9537.html
第七章
jvm的运行时数据区
https://docs.oracle.com/javase/specs/jvms/se8/html/index.html
Metaspace
http://ifeve.com/jvm-troubleshooting-guide-4/
压缩类空间
https://blog.csdn.net/jijijijwwi111/article/details/51564271
CodeCache
https://blog.csdn.net/yandaonan/article/details/50844806
http://engineering.indeedblog.com/blog/2016/09/job-search-web-app-java-8-migration/
GC调优指南：
https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/toc.html
如何选择垃圾收集器
https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/collectors.html
G1最佳实践
https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/g1_gc_tuning.html#recommendations
G1 GC的一些关键技术
https://zhuanlan.zhihu.com/p/22591838
CMS日志格式
https://blogs.oracle.com/poonam/understanding-cms-gc-logs
G1日志格式
https://blogs.oracle.com/poonam/understanding-g1-gc-logs
GC日志分析工具
http://gceasy.io/
GCViewer
https://github.com/chewiebug/GCViewer
ZGC：
http://openjdk.java.net/jeps/333
第八章
java虚拟机规范
https://docs.oracle.com/javase/specs/jvms/se8/html/index.html
java语言规范
https://docs.oracle.com/javase/specs/jls/se8/html/index.html
javap：
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/javap.html
字段描述符
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.3.2
方法描述符
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.3.3
字节码指令：
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html
常量池：
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4
本地变量表：
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-2.html#jvms-2.6.1
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.13
操作数栈：
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-2.html#jvms-2.6.2
Code属性：
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.3
LineNumberTable：
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.12
constant variable：
https://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.12.4
常量表达式
https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.28
String.intern
https://blog.csdn.net/goldenfish1919/article/details/80410349
String去重
https://blog.csdn.net/goldenfish1919/article/details/20233263
