Java9 gc log parameter migration

  java

Order

This article mainly studies the migration of java9 gc log parameters.

Logging to unify JVM and GC

Java9 has introduced a unified log framework and configured the output of gc log uniformly.

相关JEP(JDK Enhancement Proposal)

Xlog syntax

-Xlog[:option]
    option         :=  [<what>][:[<output>][:[<decorators>][:<output-options>]]]
                       'help'
                       'disable'
    what           :=  <selector>[,...]
    selector       :=  <tag-set>[*][=<level>]
    tag-set        :=  <tag>[+...]
                       'all'
    tag            :=  name of tag
    level          :=  trace
                       debug
                       info
                       warning
                       error
    output         :=  'stderr'
                       'stdout'
                       [file=]<filename>
    decorators     :=  <decorator>[,...]
                       'none'
    decorator      :=  time
                       uptime
                       timemillis
                       uptimemillis
                       timenanos
                       uptimenanos
                       pid
                       tid
                       level
                       tags
    output-options :=  <output_option>[,...]
    output-option  :=  filecount=<file count>
                       filesize=<file size in kb>
                       parameter=value

what

Mainly configure tag and level

tag

Where all represents all tags, the others are as follows:

add,age,alloc,annotation,aot,arguments,attach,barrier,biasedlocking,blocks,bot,breakpoint,bytecode,census,class,classhisto,cleanup,compaction,comparator,constraints,constantpool,coops,cpu,cset,data,defaultmethods,dump,ergo,event,exceptions,exit,fingerprint,freelist,gc,hashtables,heap,humongous,ihop,iklass,init,itables,jfr,jni,jvmti,liveness,load,loader,logging,mark,marking,metadata,metaspace,method,mmu,modules,monitorinflation,monitormismatch,nmethod,normalize,objecttagging,obsolete,oopmap,os,pagesize,parser,patch,path,phases,plab,preorder,promotion,protectiondomain,purge,redefine,ref,refine,region,remset,resolve,safepoint,scavenge,scrub,setting,stackmap,stacktrace,stackwalk,start,startuptime,state,stats,stringdedup,stringtable,subclass,survivor,sweep,system,task,thread,time,timer,tlab,unload,update,verification,verify,vmoperation,vtables,workgang

level

It is mainly divided into off, trace, debug, info, warning, error.

output

- stdout(`Sends output to stdout`)
- stderr(`Sends output to stderr`)
- file=filename(`Sends output to text file(s)`)

As in the above three types, if file is specified, the pid of the current jvm can be represented by the %p variable, and the startup timestamp of the jvm can be represented by% t. such as

-Xlog:gc:demoapp-gc-%p-%t.log

The output file name is as follows:

demoapp-gc-1678-2018-03-01_21-44-18.log

decorators

  • time — Current time and date in ISO-8601 format
  • uptime — Time since the start of the JVM in seconds and milliseconds (e.g., 6.567s)
  • timemillis — The same value as generated by System.currentTimeMillis()
  • uptimemillis — Milliseconds since the JVM started
  • timenanos — The same value as generated by System.nanoTime()
  • uptimenanos — Nanoseconds since the JVM started
  • pid — The process identifier
  • tid — The thread identifier
  • level — The level associated with the log message
  • tags — The tag-set associated with the log message

If not specified, the default is uptime, level, and tags. such as

[3.080s][info][gc,cpu        ] GC(5) User=0.03s Sys=0.00s Real=0.01s

Example

-Xlog:gc=trace:file=gctrace.txt:uptimemillis,pid:filecount=5,filesize=1024

Tag is gc, levle is trace, number of rotate files is 5, each file is 1M, file name is gctrace.txt, decrotators are uptimemillis and pid.

Output instance

[1110ms][1867] GC(2) Pause Remark 17M->17M(256M) 2.024ms
[1110ms][1867] GC(2) Finalize Live Data 0.000ms
[1110ms][1867] GC(2) Pause Cleanup 17M->17M(256M) 0.177ms
[1112ms][1867] GC(2) Concurrent Cycle 7.470ms
[2951ms][1867] GC(3) Pause Initial Mark (Metadata GC Threshold) 149M->30M(256M) 27.175ms
[2951ms][1867] GC(4) Concurrent Cycle
[2972ms][1867] GC(4) Pause Remark 32M->32M(256M) 5.132ms
[2974ms][1867] GC(4) Finalize Live Data 0.000ms
[2974ms][1867] GC(4) Pause Cleanup 32M->32M(256M) 0.214ms
[2976ms][1867] GC(4) Concurrent Cycle 25.422ms

Migration

Migration of Parameters Related to Previous Versions of GC

Legacy Garbage Collection (GC) Flag Xlog Configuration Comment
G1PrintHeapRegions -Xlog:gc+region=trace Not Applicable
GCLogFileSize No configuration available Log rotation is handled by the framework.
NumberOfGCLogFiles Not Applicable Log rotation is handled by the framework.
PrintAdaptiveSizePolicy -Xlog:ergo*=level Use a level of debug for most of the information, or a level of trace for all of what was logged for PrintAdaptiveSizePolicy.
PrintGC -Xlog:gc Not Applicable
PrintGCApplicationConcurrentTime -Xlog:safepoint Note that PrintGCApplicationConcurrentTime and PrintGCApplicationStoppedTime are logged on the same tag and aren’t separated in the new logging.
PrintGCApplicationStoppedTime -Xlog:safepoint Note that PrintGCApplicationConcurrentTime and PrintGCApplicationStoppedTime are logged on the same tag and not separated in the new logging.
PrintGCCause Not Applicable GC cause is now always logged.
PrintGCDateStamps Not Applicable Date stamps are logged by the framework.
PrintGCDetails -Xlog:gc* Not Applicable
PrintGCID Not Applicable GC ID is now always logged.
PrintGCTaskTimeStamps -Xlog:task*=debug Not Applicable
PrintGCTimeStamps Not Applicable Time stamps are logged by the framework.
PrintHeapAtGC -Xlog:gc+heap=trace Not Applicable
PrintReferenceGC -Xlog:ref*=debug Note that in the old logging, PrintReferenceGC had an effect only if PrintGCDetails was also enabled.
PrintStringDeduplicationStatistics -Xlog:stringdedup*=debug Not Applicable
PrintTenuringDistribution -Xlog:age*=level Use a level of debug for the most relevant information, or a level of trace for all of what was logged for PrintTenuringDistribution.
UseGCLogFileRotation Not Applicable What was logged for PrintTenuringDistribution.

Legacy runtime parameter migration

Legacy Runtime Flag Xlog Configuration Comment
TraceExceptions -Xlog:exceptions=info Not Applicable
TraceClassLoading -Xlog:class+load=level Use level=info for regular information, or level=debug for additional information. In Unified Logging syntax, -verbose:class equals -Xlog:class+load=info,class+unload=info.
TraceClassLoadingPreorder -Xlog:class+preorder=debug Not Applicable
TraceClassUnloading -Xlog:class+unload=level Use level=info for regular information, or level=trace for additional information. In Unified Logging syntax, -verbose:class equals -Xlog:class+load=info,class+unload=info.
VerboseVerification -Xlog:verification=info Not Applicable
TraceClassPaths -Xlog:class+path=info Not Applicable
TraceClassResolution -Xlog:class+resolve=debug Not Applicable
TraceClassInitialization -Xlog:class+init=info Not Applicable
TraceLoaderConstraints -Xlog:class+loader+constraints=info Not Applicable
TraceClassLoaderData -Xlog:class+loader+data=level Use level=debug for regular information or level=trace for additional information.
TraceSafepointCleanupTime -Xlog:safepoint+cleanup=info Not Applicable
TraceSafepoint -Xlog:safepoint=debug Not Applicable
TraceMonitorInflation -Xlog:monitorinflation=debug Not Applicable
TraceBiasedLocking -Xlog:biasedlocking=level Use level=info for regular information, or level=trace for additional information.
TraceRedefineClasses -Xlog:redefine+class*=level level=info, =debug, and =trace provide increasing amounts of information.

Summary

Java9 unifies the configuration of gc log into Xlog and can migrate according to the old and new parameter mapping tables given by the government.

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