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)
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
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
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. |
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。
