jvm 虚拟机日志参数
官网：https://docs.oracle.com/en/java/javase/14/docs/specs/man/java.html#advanced-runtime-options-for-java
*******************************
-Xlog 命令格式
-Xlog[:[selections][:[output][:[decorators][:output-options]]]]-Xlog：开启日志输出，默认为-Xlog:all=warning:stdout:uptime,level,tags
-Xlog:help：查看-Xlog参数使用方式
-Xlog:disable：禁用-Xlog日志输出
常用日志参数
-Xlog:gc：输出gc日志
-Xlog:gc*：输出详细gc日志
-Xlog:gc+heap=debug：输出gc前后堆信息，等同于-XX:+PrintHeapAtGC，java9及之后使用
-Xlog:safepoint：输出gc过程中用户线程并发及停顿时间
-Xlog:gc+age=trace：输出gc后，新生代的年龄
**********************
selections：tags + level，可选
tags
Available log tags:
add, age, alloc, annotation, aot, arguments, attach, barrier, biasedlocking, blocks,
bot, breakpoint, bytecode, cds, census, class, classhisto, cleanup, codecache,
compaction, compilation, constantpool, constraints, container, coops, cpu, cset, data,
datacreation, dcmd, decoder, defaultmethods, director, dump, dynamic, ergo, event,
exceptions, exit, fingerprint, free, freelist, gc, handshake, hashtables, heap,
humongous, ihop, iklass, init, inlining, install, interpreter, itables, jfr, jit, jni,
jvmti, liveness, load, loader, logging, malloc, mark, marking, membername, memops,
metadata, metaspace, methodcomparator, mirror, mmu, module, monitorinflation,
monitormismatch, nestmates, nmethod, normalize, numa, objecttagging, obsolete, oldobject,
oom, oopmap, oops, oopstorage, os, pagesize, parser, patch, path, perf, periodic, phases,
plab, preorder, preview, promotion, protectiondomain, ptrqueue, purge, record, redefine,
ref, refine, region, reloc, remset, resolve, safepoint, sampling, scavenge, setting, smr,
stackmap, stacktrace, stackwalk, start, startuptime, state, stats, streaming,
stringdedup, stringtable, subclass, survivor, sweep, symboltable, system, table, task,
thread, time, timer, tlab, tracking, unload, unshareable, update, verification, verify,
vmmutex, vmoperation, vmthread, vtables, vtablestubs, workgang
Specifying 'all' instead of a tag combination matches all tag combinations.
level： off, trace, debug, info, warning, error
示例：
all：包含所有标签
gc：只有gc标签的日志
gc*：包含gc的标签
gc + phases：只有gc、phrases的日志，单独的gc、phases不输出
gc + phases*：输出包含gc、phases的日志
gc=trace：输出日志级别在trace或以上的日志
**********************
output：输出位置
stdout：输出到控制台
stderr：错误输出
file=file_name：输出到文件
**********************
decorations：日志输出格式，可选，默认为uptime，level，tags
time、t：当前时间，当前时区时间，如：[2020-04-02T16:17:54.614+0800]
utctime、utc：通用时间，0时区时间，如：[2020-04-02T08:17:54.614+0000]
timemills、tm：System.currentTimeMillis()的数值，如：[1585815474614ms]
timenanos、tn：System.nanoTime()的数值，如：[108171620762600ns]
uptime、u：虚拟机启动到当前时间间隔，如：[0.179s]
uptimemillis、um：虚拟机启动经过的毫秒数，如：[171ms]
uptimenanos、un：虚拟机启动到当前经过的时间，纳秒，如：[108303677015300ns]
hostname、hn：主机名
pid、p：进程id
tid、ti：线程id
level、l：日志级别
tags、tg：标签名
*******************************
示例
public class Test {
public static void main(String[] args){
byte[] b=new byte[1024*1024];
b=null;
System.gc();
}
}
**********************
控制台输出
虚拟机参数：-XX:+UseParallelGC -Xlog:gc*:stdout:time,utc,uptime,hostname,pid,tid,level,tags
[2020-04-02T16:30:54.480+0800][2020-04-02T08:30:54.480+0000][0.027s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,coops] Heap address: 0x0000000081c00000, size: 2020 MB, Compressed Oops mode: 32-bit
[2020-04-02T16:30:54.483+0800][2020-04-02T08:30:54.483+0000][0.028s][LAPTOP-D73GD8TE][6480][1664][info][gc ] Using Parallel
[2020-04-02T16:30:54.600+0800][2020-04-02T08:30:54.600+0000][0.146s][LAPTOP-D73GD8TE][6480][4388][info][gc,start ] GC(0) Pause Young (System.gc())
[2020-04-02T16:30:54.602+0800][2020-04-02T08:30:54.602+0000][0.148s][LAPTOP-D73GD8TE][6480][4388][info][gc,heap ] GC(0) PSYoungGen: 9472K(38400K)->968K(38400K) Eden: 9472K(33280K)->0K(33280K) From: 0K(5120K)->968K(5120K)
[2020-04-02T16:30:54.602+0800][2020-04-02T08:30:54.602+0000][0.148s][LAPTOP-D73GD8TE][6480][4388][info][gc,heap ] GC(0) ParOldGen: 0K(87552K)->8K(87552K)
[2020-04-02T16:30:54.602+0800][2020-04-02T08:30:54.602+0000][0.148s][LAPTOP-D73GD8TE][6480][4388][info][gc,metaspace ] GC(0) Metaspace: 624K(4864K)->624K(4864K) NonClass: 566K(4352K)->566K(4352K) Class: 58K(512K)->58K(512K)
[2020-04-02T16:30:54.602+0800][2020-04-02T08:30:54.602+0000][0.148s][LAPTOP-D73GD8TE][6480][4388][info][gc ] GC(0) Pause Young (System.gc()) 9M->0M(123M) 1.999ms
[2020-04-02T16:30:54.602+0800][2020-04-02T08:30:54.602+0000][0.148s][LAPTOP-D73GD8TE][6480][4388][info][gc,cpu ] GC(0) User=0.00s Sys=0.00s Real=0.00s
[2020-04-02T16:30:54.602+0800][2020-04-02T08:30:54.602+0000][0.148s][LAPTOP-D73GD8TE][6480][4388][info][gc,start ] GC(1) Pause Full (System.gc())
[2020-04-02T16:30:54.602+0800][2020-04-02T08:30:54.602+0000][0.148s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases,start] GC(1) Marking Phase
[2020-04-02T16:30:54.604+0800][2020-04-02T08:30:54.604+0000][0.149s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases ] GC(1) Marking Phase 1.591ms
[2020-04-02T16:30:54.604+0800][2020-04-02T08:30:54.604+0000][0.150s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases,start] GC(1) Summary Phase
[2020-04-02T16:30:54.604+0800][2020-04-02T08:30:54.604+0000][0.150s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases ] GC(1) Summary Phase 0.015ms
[2020-04-02T16:30:54.604+0800][2020-04-02T08:30:54.604+0000][0.150s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases,start] GC(1) Adjust Roots
[2020-04-02T16:30:54.605+0800][2020-04-02T08:30:54.605+0000][0.150s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases ] GC(1) Adjust Roots 0.652ms
[2020-04-02T16:30:54.605+0800][2020-04-02T08:30:54.605+0000][0.150s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases,start] GC(1) Compaction Phase
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases ] GC(1) Compaction Phase 2.365ms
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases,start] GC(1) Post Compact
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc,phases ] GC(1) Post Compact 0.048ms
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc,heap ] GC(1) PSYoungGen: 968K(38400K)->0K(38400K) Eden: 0K(33280K)->0K(33280K) From: 968K(5120K)->0K(5120K)
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc,heap ] GC(1) ParOldGen: 8K(87552K)->925K(87552K)
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc,metaspace ] GC(1) Metaspace: 624K(4864K)->624K(4864K) NonClass: 566K(4352K)->566K(4352K) Class: 58K(512K)->58K(512K)
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc ] GC(1) Pause Full (System.gc()) 0M->0M(123M) 4.869ms
[2020-04-02T16:30:54.607+0800][2020-04-02T08:30:54.607+0000][0.153s][LAPTOP-D73GD8TE][6480][4388][info][gc,cpu ] GC(1) User=0.00s Sys=0.00s Real=0.01s
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.153s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] Heap
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] PSYoungGen total 38400K, used 1664K [0x00000000d5f00000, 0x00000000d8980000, 0x0000000100000000)
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] eden space 33280K, 5% used [0x00000000d5f00000,0x00000000d60a01e8,0x00000000d7f80000)
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] from space 5120K, 0% used [0x00000000d7f80000,0x00000000d7f80000,0x00000000d8480000)
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] to space 5120K, 0% used [0x00000000d8480000,0x00000000d8480000,0x00000000d8980000)
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] ParOldGen total 87552K, used 925K [0x0000000081c00000, 0x0000000087180000, 0x00000000d5f00000)
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] object space 87552K, 1% used [0x0000000081c00000,0x0000000081ce76d0,0x0000000087180000)
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] Metaspace used 627K, capacity 4531K, committed 4864K, reserved 1056768K
[2020-04-02T16:30:54.608+0800][2020-04-02T08:30:54.608+0000][0.154s][LAPTOP-D73GD8TE][6480][1664][info][gc,heap,exit ] class space used 58K, capacity 402K, committed 512K, reserved 1048576K
