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序

本文主要研究一下java9 gc log参数的迁移。

统一JVM及GC的Logging

java9引进了一个统一的日志框架，把gc相关的log输出及配置也给纳入进来了。

相关JEP(JDK Enhancement Proposal)

• JEP 158: Unified JVM Logging

• JEP 264: Platform Logging API and Service

• JEP 271: Unified GC Logging

Xlog语法

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

what

主要是配置tag及level

tag

其中all代表所有的tag，其他的如下：

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

主要分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)`)

有如上三种，其中指定file的话，可以使用%p变量表示当前jvm的pid，用%t表示jvm的启动时间戳。比如

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

输出的文件名如下：

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

不指定的话，默认是uptime, level, and tags这三个。比如

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

实例

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

tag为gc，levle为trace，rotate文件数为5，每个文件1M，文件名为gctrace.txt，decrotators为uptimemillis和pid

输出实例

[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

迁移

旧版GC相关参数迁移

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.

旧版运行时参数迁移

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.

小结

java9把gc log的选型及输出也给统一到了Xlog中，可以按照官方给出的迁移表进行迁移。

感谢各位的阅读，以上就是“java9中gc log参数的迁移”的内容了，经过本文的学习后，相信大家对java9中gc log参数的迁移这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是创新互联，小编将为大家推送更多相关知识点的文章，欢迎关注！

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