GC log parameter migration in java9

sequence

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

Logging that unifies JVM and GC

Java9 has introduced a unified log framework, and has also included gc-related log output and configuration.

Related JEP(JDK Enhancement Proposal)

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

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, classshisto, cleanup, compaction, comparator, constraints, constantpool, coops, cpu, cset, data, defaultmethods, d ump, 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, mu, modules, monitorinflatio n, monitormismatch, nmethod, normalize, objecttagging, obsolete, ooopmap, os, pagesize, parser, patch, path, phases, plab, preorder, promotion, protectiondomain, purge, redefine, ref, refine, region, remset, resolve, safepoint, scange, scru b, setting, stackmap, stacktrace, stackwalk, start, startuptime, state, stats, stringdedup, stringtable, subclass, survivor, sweep, system, task, thread, time, timer, tlab, unload, update, verification, verification, 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)`)

There are three types as above. If you specify a file, you can use the %p variable to represent the current jvm's pid and use %t to represent the start time stamp of jvm. 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 million seconds (eg, 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. for example

 [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, rotate files are 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

migrate

Migration of related parameters of old GC

Legacy runtime parameter migration

summary

Java9 also unifies the selection and output of gc log into Xlog, and can be migrated according to the migration table given by the official.