Gc log parameter migration in Java 9 and java9gclog migration

Gc log parameter migration in Java 9 and java9gclog migration
Collation

This article mainly studies the migration of gc log parameters in Java 9.

Unified JVM and GC Logging

Java 9 introduces a unified log framework to include gc-related log output and configuration.

JEP (JDK Enhancement Proposal)

• JEP 158: uniied JVM Logging
• JEP 264: Platform Logging API and Service
• JEP 271: uniied GC Logging
  

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

It mainly configures the tag and level.

Tag

All indicates all tags, and 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

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)`)

If file is specified, the % p variable can be used to represent the pid of the current jvm, and % t can be used to represent the jvm startup timestamp. For example

-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., 6.567 s)
• 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 this parameter is not specified, the default value is uptime, level, and tags. For example

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

Instance

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

Tagis gc, levleis trace, rotatefile number is 5, each file is 1 m, the file name is gctrace.txt, decrotators is 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 GC-related parameters in earlier versions

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.

Parameter migration in earlier versions

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 uniied 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 uniied 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

Java 9 unifies the selection and output of gc logs into Xlog, which can be migrated according to the migration table officially provided.