jcmd #javacasual

jcmd 便利
KUBOTA Yuji @sugarlife <kubota.yuji@gmail.com>
NTT OSS Center
2016/Nov/07
Copyright©2016 NTT corporation

Who I am
KUBOTA Yuji (@sugarlife)
* Java Technical Support Engineer at NTT
* OpenJDK author, Icedtea committer, Speaker
HeapStats/heapstats

•Introduction to Troubleshooting in JDK 9
•jcmd と jhsdb を使おう
•スライド：https://goo.gl/4jaujJ
JDK 9 からの診断ツール

Java 8

•Introduction to Troubleshooting in JDK 9
•JDK 9 では jcmd / jhsdb を使おうという話
•スライド：https://goo.gl/4jaujJ
JavaOne 2016
% jstack # JDK 8
:
Options:
-F to force a thread dump. Use when jstack <pid> does not respond (process is hung)
-m to print both java and native frames (mixed mode)
-l long listing. Prints additional information about locks
-h or -help to print this help message
% ./jstack # JDK 9
:
Options:
-l long listing. Prints additional information about locks
-h or -help to print this help message
# -F was removed by JDK-8155091: Remove SA related functions from tmtools
% ./jstack -m
Error: -m option used
Cannot connect to core dump or remote debug server. Use jhsdb jstack instead
% ./jhsdb jstack --mixed
You have to set --pid or --exe.
--locks to print java.util.concurrent locks
--mixed to print both java and native frames (mixed mode)
--exe executable image name
--core path to coredump
--pid pid of process to attach

•jcmd process help
•実行可能なコマンド一覧 (対象プロセス依存)
•jcmd process help command
•コマンドのヘルプ(使い方、負荷、オプション等)
Help
% jcmd 999 help GC.run
999:
GC.run
Call java.lang.System.gc().
Impact: Medium: Depends on Java heap size and content.
Syntax: GC.run

Command: Domain.suffix (Java 8)
Domain
Num.
suffix
Abstract
PerfCounter 1 各種 JVM 統計情報 (※)
ManagementAgent 3 JMX エージェント操作
Thread 1 スレッドダンプ
GC 7 GC 機構 (Heap / GC / Finalization)
VM 7 ランタイム操作、情報取得
※: 本来はコマンドとは別枠だが、見易さのため並べて記載している

Command: Domain.suffix (Java 9)
Domain
Num.
suffix
Abstract
PerfCounter 1 - 各種 JVM 統計情報 (※)
ManagementAgent 4 +1 JMX エージェント操作
Thread 1 - スレッドダンプ
GC 7 +2
-1
GC 機構 (Heap / GC / Finalization)
VM 15 +8 ランタイム操作、情報取得
Compiler 7 - コンパイラ操作、情報取得
JVMTI 2 - JVMTI エージェント操作
GC.rotate_log が VM ドメインへ移動
※: 本来はコマンドとは別枠だが、見易さのため並べて記載している

•JVM 統計情報
•jstat や jinfo はこれを基に加工して出力してる
• jdk/src/jdk.jcmd/share/classes/sun/tools/jstat/resources/jstat_options
•無加工は辛いので加工スクリプトに渡して出
力すると便利
PerfCounter
suffix Description
print JVM 統計情報を出力

•Management Agent 起動したり終わらせたり
•JMX (Management Extensions) と JDP(Discovery Protocol)
• JMXリモートアクセスを忘れてても後から設定可能
ManagementAgent
suffix Description
status 状態表示
start リモートエージェントを有効化
start_local ローカルエージェントを有効化
stop リモートエージェントを無効化
JDK 9 から

$ jcmd 999 ManagementAgent.start jmxremote.port=777 jmxremote.ssl=true
999:
Commandexecuted successfully
$ jcmd 999 ManagementAgent.status
Agent: enabled
Connection Type: remote
Protocol : rmi
Host : fedora24.novalocal
URL : service:jmx:rmi://XXX…XXX
Properties :
com.sun.management.jmxremote.authenticate = true [default]
com.sun.management.jmxremote.ssl.need.client.auth = false [default]
com.sun.management.jmxremote.ssl = true [default]
:
com.sun.management.jmxremote.port = 8070
[config.file | jmxremote.* | jdp.*]

•Thread
•mixed モードが欲しい場合は
% jhsdb jstack --mixed --pid <pid>
Thread
suffix Description
print Thread dump

•GC機構 (Heap/GC/Finalization)
GC
suffix Description
class_stats* クラスメタデータ一覧 (-helpで各項目説明)
class_histogram クラスヒストグラム (jmap -histo:live)
heap_info ヒープ・メタスペース使用量
heap_dump ヒープダンプ (jmap -dump, -allで参照切れも)
finalizer_info Finalize 待ちキュー表示
run_finalization Finalization 実行 (System#runFinalization)
run GC 実行 (System#gc)
*:要 -XX:+UnlockDiagnosticVMOptions
参考：hotspot/src/share/vm/runtime/globals.hpp

•ランタイム周り。情報出力系
VM
suffix Description
info Fatal Error Log (クラッシュ時等で出すログ)
uptime 起動時間
command_line VM 引数
system_properties システムプロパティ
version バージョン
flags 設定した(された)フラグ (-all で全フラグ)
dynlibs メモリマップ付き Dynamic library リスト

•ランタイム周り。情報出力・動作変更系
VM
suffix Description
print_touched_methods* JVM 実行中に触ったメソッドを表示
classloader_stats メタデータ状況等の全クラスローダ情報
class_hierarchy 読込クラスをクラスローダ付き階層表示
native_memory** Native Memory Tracking (NMT)
stringtable StringTable (-verboseで全Stringダンプ)
symboltable SymbolTable (-verboseで全シンボル)
set_flag flgname [value] JVM フラグの設定 (一部のみ)
*:要 -XX:+UnlockDiagnosticVMOptions
**: 要 -XX:NativeMemoryTracking 設定

• Native メモリの状態を記録する
1. Run Java with -XX:NativeMemoryTracking=summary
2. jcmd 999 VM.native_memory baseline
3. jcmd 999 VM.native_memory summary.diff
• 詳細に見たい場合は上の summary を details に変える
• NativeMemoryTracking was available since Java 8
• https://docs.oracle.com/javase/8/docs/technotes/
guides/troubleshoot/tooldescr007.html
Native Memory Tracking

$ jcmd 999 VM.native_memory baseline
999:
Baseline succeeded
# --- Run method which wants to check the memory consumption ---
$ jcmd 999 VM.native_memory summary.diff
999:
Native Memory Tracking:
Total: reserved=5664359KB -36096KB, committed=371555KB -36096KB
- Java Heap (reserved=4108288KB, committed=258048KB)
(mmap: reserved=4108288KB, committed=258048KB)
- Class (reserved=1056953KB +15KB, committed=5433KB +15KB)
(classes #767 +3)
(malloc=185KB +3KB #741 -4)
(mmap: reserved=1056768KB, committed=5248KB)
- Thread (reserved=36128KB -112KB, committed=36128KB -112KB)
(thread #36 +1)
(stack: reserved=35980KB +325KB, committed=35980KB+325KB)
(malloc=107KB +2KB #197 +4)
(arena=41KB -130KB #70 +2)
:
Native Memory Tracking
±n shows diff from baseline

•ランタイム周り。ログ。
• -XX:+PrintGCDetails -Xloggc:gc.log.`date +%Y-
%m-%d_%H-%M-%S` -XX:+PrintGCTimeStamps
• -Xlog:gc*=debug:gc.log.%t:time,level
• -Xlog:[<selection>]:[<output>]:[<decorators>]
VM
suffix Description
log JVM Unified Logging (JEP158) 制御

•jcmd 999 VM.log [options]
•-Xlog:[<selection>]:[<output>]:[<decorators>]
GC ログを設定するケース
Options Description
output output (出力先)
output_options output (その他の設定)
what selection (ロギング対象とそのレベル)
decorators decorators (出力内容調整)
disable Clears all configurations and turns off all loggings
list Lists current log configurations
rotate Rotate all logs (instead of GC.log_rotate in Java 8)

•Confirms current loggings
$ jcmd 999 VM.log list
999:
Available log levels: off, trace, debug, info, warning, error
Available log decorators: time (t), uptime (u), timemillis (tm), …
Available log tags: add, age, alloc, arguments, annotation, barrier, …
:
Described tag combinations:
logging: Logging for the log framework itself
Log output configuration:
#0: stdout all=warning uptime,level,tags
#1: stderr all=off uptime,level,tags
default configurations

•Turns on a new logging: GC.log
$ jcmd 999 VM.log output="file=gc.log"
output_options="filecount=5,filesize=10m"
what="gc=debug" decorators="time,level"
999:
Command executed successfully
999:
:
#2: gc.log gc=debug time,level added a new GC logging
gc=log_level
name or path
options (log
rotation)

•Turns off all existing loggings
•If you want to turn off #2 only
•jcmd 999 VM.log output="#2" what="all=off"
$ jcmd 999 VM.log disable
999:
Command executed successfully
999:
:
#0: stdout all=off uptime,level,tags
set all=off at stdout / stderr, and removed
the other configuration(s) such as #2
output nothing

•jcmd 999 VM.log rotate
•Rotates logs satisfying the following
1. Configured ‘output’ as file
2. Configured ‘filecount’ (by ‘output_option’)
手動ログローテート
:
#2: gc.log gc=debug filecount=5,filesize=20M level,tags
#2 will be rotated,
not #0 and #1
Obsoleted GC.rotate_log

•JIT Compiler
•JEP 165: Compiler Control (JDK 9 Feature)
Compiler
suffix Description
directive_add Adds directives of JIT by JSON format same as -XX:CompilerDirectivesFile
directive_remove Removes a latest directive
directive_clear Clears all directives
directive_print Prints current directives
codecache Prints summary of code cache
codelist Lists all code cache
queue Lists methods in waiting queue for JIT

% cat disable_c2_at_string-hashCode.json
[
{
"match":[ "*String.hashCode" ],
"c2":{ "Exclude":true }
}
]
% jcmd 999 Compiler.directives_add disable_c2_at_string-hashCode.json
999:
1 compiler directives added
% jcmd 999 Compiler.directives_print
999:
Directive:
matching: *String.hashCode
c1 directives:
inline: -
Enable:false Exclude:false BreakAtExecute:false Log:false PrintAssembly:false …
c2 directives:
inline: -
Enable:true Exclude:true BreakAtExecute:false Log:false PrintAssembly:false …
Switch false to true

•jcmd 999 Compiler.codelist
•Prints JIT compiled methods (in code cache)
How JIT Compiler works?
% jcmd 999 Compiler.codelist
999:
:
18 3 java.lang.String.hashCode()I [0x00007ff301594090, 0x00007ff301594280 - 0x00007ff3015946e8]
:
ID
Compile level of -XX:+TieredCompilation
0: Interpreter
1-3: C1
1: C1 without profiling (full optimization)
2: C1 with basic profiling (invocation and back-edge)
3: C1 with full profiling
4: C2
Method name nmethod start address code start address
code end address

How JIT Compiler works?
•JVM JIT compilation overview
•http://www.slideshare.net/ZeroTurnaround/vlad
imir-ivanovjvmjitcompilationoverview-
24613146
•Intrinsic Methods in HotSpot VM
•http://www.slideshare.net/RednaxelaFX/green-
teajug-hotspotintrinsics02232013

•JVMTI Agent 制御
JVMTI
suffix Description
agent_load library_path [option] Attach JVMTI agent of library path
data_dump Fire DataDumpRequest JVMTI
event
% jcmd 999 JVMTI.agent_load /path/to/libheapstats.so
% jcmd 999 JVMTI.agent_load ¥
/path/to/libheapstats.so=heapstats.conf

• DiagnosticCommandMBean (jconsole / jvisualvm)
リモートプロセスに jcmd
same as jcmd
commands
click then run jcmd
VM.system_properties
result

HeapStats
Lightweight JVMTI agent

•Gathers runtime information
continuously, then draws up
time-series graphs
•Lightweight agent to run on the
production systems
•New solution to troubleshooting
for OpenJDK users.
HeapStats

Overhead of HeapStats
467.59 461.43
0
50
100
150
200
250
300
350
400
450
500
Without HeapStats With HeapStats
(ops/m)
1.32 %
Overhead Rate
SPECjvm2008 Composite Result

$ jcmd 999 JVMTI.agent_load libheapstats.so
999:
Commandexecuted successfully
or
java.lang.OutOfMemoryError: Java heap space
$ java –jar heapstats-analyzer.jar
$ rpm -ivh heapstats-2.0.1-0.*.rpm
$ java -agentpath:heapstats … Your_Application
then
How to use HeapStats

biegebyte[]

byte[]
Most doubtful class which
has many references to byte[]

Monitor wait
Run
Sleep
Legend

•https://github.com/HeapStats/heapstats
•http://icedtea.classpath.org/wiki/HeapStats
Your contributions are welcome!

おしまい
@sugarlife
kubota.yuji@gmail.com

jcmd #javacasual

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