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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 := [<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

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。