Garbage First Garbage Collection (G1 GC) #jjug_ccc #ccc_cd6

Garbage First Garbage Collection (G1 GC) #jjug_ccc #ccc_cd6

1. 1. Garbage First GC KUBOTA Yuji @sugarlife NTT OSSセンタ Copyright©2015 NTT corp. All Rights Reserved. 2015/11/28 JJUG CCC 2015 Fall #ccc_cd6
2. 2. @sugarlife #ccc_cd6 #jjug 感想や質問はぜひ Twitter で！ Copyright©2015 NTT corp. All Rights Reserved. 2
3. 3. はじめに • 本セッションでは Garbage First GC (G1 GC) について、ログから 動作状況を把握できる、主に開 発者・運用者向けの知識の土台 作りを目標としています 体系的な知識の土台作りが目標 Copyright©2015 NTT corp. All Rights Reserved. 3
4. 4. おやくそく • 本セッション (スライド) における 表現は全て個人の見解です • 以下の JVM 実装に基づきます –HotSpot VM (OpenJDK 8) –repo jdk8u/jdk8u-dev/hotspot •changeset 7664:831754f092fb(zip) 動作確認は jdk8u66 でやりました Copyright©2015 NTT corp. All Rights Reserved. 4
5. 5. KUBOTA Yuji @sugarlife • OpenJDK テクニカルサポート –コア解析からGCチューニング, etc… • 解析支援ツール HeapStats 開発 –多数の商用で元気に稼働中 :) • 難聴者 –資料的なスライドを多用します 過去にCMS GC, Jigsaw, HeapStats を発表 Copyright©2015 NTT corp. All Rights Reserved. 5
6. 6. NTT OSSセンタ • NTT グループの OSS 活用を支える部隊 *)OSSVERT®：OSs Suites VERified Technically（技術検証済みOSS組合せ） 事業会社 SI会社 問合せ対応、導 入支援、保守等 技術検証、 導入推進 プロダクト/ ツール類開発 技術者育成、 人材交流 各種 OSS コ ミュニ ティ 設計, 開 発, 運用 グループ各社 サポー トベン ダ、 NTT 研究所 等お 客 様 サポー ト連携 開発 連携 ①OSSトータル サポート NTT OSSセンタ ②OSS適用推進 (OSSVERT®*検証) ③技術開発 (DBMS,高可用ミドル等) ④ソフトウェア 基盤技術力向上 Kernel, PostgreSQL, Pacemaker, Tomcat, etc Copyright©2015 NTT corp. All Rights Reserved. 6
7. 7. OpenJDK Contributes Copyright©2015 NTT corp. All Rights Reserved. 7 暗号化 zip 操作 API を提案中！ 興味ある人は是非MLへ！
8. 8. G1 GC 概要 なぜ Garbage First なのか？ Copyright©2015 NTT corp. All Rights Reserved. 8
9. 9. Garbage Collection 1. 不要なメモリ領域(ゴミ)を判別し、 2. ゴミを処理して再利用可能にする 面倒なメモリ管理は JVM に任せたい Copyright©2015 NTT corp. All Rights Reserved. 9
10. 10. HotSpot VM の GC • Serial GC, Parallel GC –初期GC, JDK8 以前はデフォルト • Concurrent Mark-Sweep GC –JDK1.4.1 から導入 (出典:JDK-4758307) • Garbage First GC –JDK7 から導入, JDK9からデフォルト 細かく言えば他にもあるけど主流はこれら Copyright©2015 NTT corp. All Rights Reserved. 10
11. 11. Parallel と Concurrent ケースバイケースで GC を選択しましょう Copyright©2015 NTT corp. All Rights Reserved. 11 Parallel (Serial ＝ Threadが1つ) Concurrent (実際は部分的に 停止するMostly) Application Thread GC Thread アプリケーション停止＝Stop The World (STW)
12. 12. メモリ管理 今回はPerm/Metaspace等は細かく見ません Copyright©2015 NTT corp. All Rights Reserved. 12 Heap Perm / Meta space
13. 13. Heap (ヒープ) Copyright©2015 NTT corp. All Rights Reserved. 13 Heap オブジェクトが配置される Heap を巨大な 一つのデータ構造として扱うのは非効率
14. 14. ヒープ管理 (従来) Copyright©2015 NTT corp. All Rights Reserved. 14 Eden Old Survivor 0 Survivor 1 というわけで、Java (JVM)は世代別に分けて それぞれ異なる GC で管理しています Young
15. 15. ヒープ管理 (従来) Copyright©2015 NTT corp. All Rights Reserved. 15 Eden Old Survivor 0 Survivor 1 ヒープが巨大化すると結局非効率になります そこで G1 はヒープ構造を変更しました Young
16. 16. Heap Layout (G1) Copyright©2015 NTT corp. All Rights Reserved. 16 G1 では Region と呼ばれる空間に ヒープを等しく分割して管理してます
17. 17. Heap Layout (G1) Copyright©2015 NTT corp. All Rights Reserved. 17 Region のサイズは初期ヒープサイズに 依存しますが -XX:G1HeapRegionSize で 1～32MBの範囲で変更が可能です
18. 18. Heap Layout (G1) Copyright©2015 NTT corp. All Rights Reserved. 18 Region のサイズは初期ヒープサイズに 依存しますが -XX:G1HeapRegionSize で 1～32MBの範囲で変更が可能です Regionサイズの半分以上の単体オブジェクトは 「Humongous Object」として扱われます
19. 19. 世代分け Copyright©2015 NTT corp. All Rights Reserved. 19 E O S O O S S E O E O O E S O O O O O E E O 水:Eden 橙:Survivor 緑:Old 藍:未使用 G1 GC も他 GC と同じく世代別 GC です Young (Eden, Survivor) 対象の Young GC Young + Old (Tenure) 対象の Mixed GC そして G1 GC が失敗した時の Full GC
20. 20. Humongous Object Copyright©2015 NTT corp. All Rights Reserved. 20 E O S O O S S E H O E O O E S O O O O H O E E O Humongous Object が生成された場合は 専用の Region にアロケートされます 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
21. 21. Humongous Object Copyright©2015 NTT corp. All Rights Reserved. 21 E O S O O S S E H O E O O E S O O O O H O E E O Humongous Object が生成された場合は 専用の Region にアロケートされます アロケート時に GC 発生の可能性がある上、 メモリ獲得コストも高いので極力生成は避ける 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
22. 22. Garbage First の所以 Copyright©2015 NTT corp. All Rights Reserved. 22 E O S O O S S E O E O O E S O O O O O E E O H H1. 各Regionの不要オブジェクト量は異なる 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
23. 23. Garbage First の所以 Copyright©2015 NTT corp. All Rights Reserved. 23 E O S O O S S E O E O O E S O O O O O E E O H H1. 各Regionの不要オブジェクト量は異なる 2. GC による回収はコスト(STW)が発生する 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
24. 24. Garbage First の所以 Copyright©2015 NTT corp. All Rights Reserved. 24 E O S O O S S E O E O O E S O O O O O E E O H H1. 各Regionの不要オブジェクト量は異なる 2. GC による回収はコスト(STW)が発生する 不要オブジェクト(ゴミ)が多いRegionだけ GC して処理時間を(できるだけ)抑える=G1 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
25. 25. Garbage First の所以 Copyright©2015 NTT corp. All Rights Reserved. 25 E O S O O S S E T E O O T E S T O O O O E E O H H1. 各Regionの不要オブジェクト量は異なる 2. GC による回収はコスト(STW)が発生する 不要オブジェクト(ゴミ)が多いRegionだけ GC して処理時間を(できるだけ)抑える=G1 アプリケーションを止めないコンカレント サイクルでマーキングを実施する 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
26. 26. Garbage First の所以 Copyright©2015 NTT corp. All Rights Reserved. 26 E O S O O S S E T E O O T E S T O O O O E E O H H1. 各Regionの不要オブジェクト量は異なる 2. GC による回収はコスト(STW)が発生する 不要オブジェクト(ゴミ)が多いRegionだけ GC して処理時間を(できるだけ)抑える=G1 アプリケーションを止めないコンカレント サイクルでマーキングを実施する -XX:MaxGCPauseMillis で指定した値を 目安に前向きに善処 (デフォルト 200ms) 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
27. 27. まとめ Copyright©2015 NTT corp. All Rights Reserved. 27 • ヒープレイアウト –従来と同じく世代別に領域を分ける。 ただし、巨大ヒープを効率的に処理 するため、Region に細分化 • G1 処理 –マーキングはコンカレントサイクル –Young GC と Mixed GC の世代別GC –失敗した場合は Full GC が発生する ゴミの多い場所を優先してやるから G1 GC
28. 28. G1 処理とログ 処理を具体的に追っていきましょう Copyright©2015 NTT corp. All Rights Reserved. 28
29. 29. Copyright©2015 NTT corp. All Rights Reserved. 29 以降のログ出力に利用したオプションです G1 使用時の推奨値とは別なのに注意 ログについて 使用した Java 起動オプション -XX:+UseG1GC -XX:+PrintGCDetails -XX:+PrintGCCause -XX:+PrintGCDateStamps 見やすいようにタイムスタンプを除 外し、一部省略や改行をしています 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
30. 30. Copyright©2015 NTT corp. All Rights Reserved. 30 オブジェクトの生成 E E 生成オブジェクトは Eden に配置され、 Eden が一杯になると Young GC が発生 O O S H 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
31. 31. Copyright©2015 NTT corp. All Rights Reserved. 31 オブジェクトの生成 E E 生成オブジェクトは Eden に配置され、 Eden が一杯になると Young GC が発生 O O E S H 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
32. 32. Copyright©2015 NTT corp. All Rights Reserved. 32 オブジェクトの生成 E E 生成オブジェクトは Eden に配置され、 Eden が一杯になると Young GC が発生 O O E E S H 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
33. 33. Copyright©2015 NTT corp. All Rights Reserved. 33 Young GC E E Young GC が発生した際はこの形式の ログが出力。GC Causeは複数種類あります O O E E S H [GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] GC発生原因(GC Cause) young/mixed 識別箇所 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
34. 34. Copyright©2015 NTT corp. All Rights Reserved. 34 Young GC E E E E O O S 全 Eden / Survivor をスキャンし、生存オブ ジェクトを新Survivorに退避 (Evacuation) H 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
35. 35. Copyright©2015 NTT corp. All Rights Reserved. 35 Young GC E S E S E S E O O S 全 Eden / Survivor をスキャンし、生存オブ ジェクトを新Survivorに退避 (Evacuation) H 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
36. 36. Copyright©2015 NTT corp. All Rights Reserved. 36 Young GC E S E S E S E O O S H Survivor の一部のオブジェクトは (年齢的に) Old に退避する場合もあります 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
37. 37. Copyright©2015 NTT corp. All Rights Reserved. 37 Young GC E S E S O E S E O O S H Survivor の一部のオブジェクトは (年齢的に) Old に退避する場合もあります 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
38. 38. Copyright©2015 NTT corp. All Rights Reserved. 38 Young GC (Survivor Full) E S E S E S E O O S H もし退避先の Survivor に生存オブジェクト を退避させるスペースがなかった場合は、 Eden から直接 Old 領域に退避することも 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
39. 39. Copyright©2015 NTT corp. All Rights Reserved. 39 Young GC (Survivor Full) E S E S E S E O O S H もし退避先の Survivor に生存オブジェクト を退避させるスペースがなかった場合は、 Eden から直接 Old 領域に退避することも 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
40. 40. Copyright©2015 NTT corp. All Rights Reserved. 40 Young GC (Survivor Full) E S E S E S E O O S H もし退避先の Survivor に生存オブジェクト を退避させるスペースがなかった場合は、 Eden から直接 Old 領域に退避することも O 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
41. 41. Copyright©2015 NTT corp. All Rights Reserved. 41 Young GC 後 O Eden / Survivor元 (from) に割り当てていた Region を解放して不要オブジェクトを回収 S S S O O H 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
42. 42. Copyright©2015 NTT corp. All Rights Reserved. 42 ログと大まかな処理の流れ[GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] 一連のログを全部表示すると、このように インデントでグルーピングされています
43. 43. [GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] Copyright©2015 NTT corp. All Rights Reserved. 43 ログと大まかな処理の流れ 特に重要なのは先頭と末尾
44. 44. [GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] Copyright©2015 NTT corp. All Rights Reserved. 44 ログと大まかな処理の流れ [GC pause (<GCCause>) (young), 0.0650323 secs] ： ： [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] 各領域のサイズと停止(STW)時間が解ります Young GC 確認
45. 45. [GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] Copyright©2015 NTT corp. All Rights Reserved. 45 ログと大まかな処理の流れ [GC pause (<GCCause>) (young), 0.0650323 secs] ： ： [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] GC前 使用量(容量) -> GC後 使用量(容量) 実 STW 時間 各領域のサイズと停止(STW)時間が解ります Young GC 確認
46. 46. Copyright©2015 NTT corp. All Rights Reserved. 46 ログと大まかな処理の流れ[GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] このグループは GC Worker による生存オブ ジェクトのスキャンと退避処理のログです
47. 47. [GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] Copyright©2015 NTT corp. All Rights Reserved. 47 ログと大まかな処理の流れ [Parallel Time: 38.6 ms, GC Workers: 10] [<ラベル>: Min:<最小>, Avg:<平均>, Max:<最大>, Diff:<最大－最少>, Sum:<全 Worker の合計値>] Worker 数 この様な形式で各ラベルごとに 並列処理に懸った時間が出力されます
48. 48. [GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] Copyright©2015 NTT corp. All Rights Reserved. 48 ログと大まかな処理の流れ [Parallel Time: X ms, GC Workers: Y] [<ラベル>: Min:<最小>, Avg:<平均>, Max:<最大>, Diff:<最大－最少>, Sum:<全 Worker の合計値>] Worker 数 GC Worker処理のラベルとその内容はこちら [GC Worker Start]:開始タイムスタンプ (VM起動時間) [Ext Root Scanning]:Heapの Root Region のスキャン [Update RS],[Scan RS]:RS(Remember Set, 新規オブジェ クトが配置されたリージョンのコレクション)のスキャン [Code Root Scanning]:Code Cache のスキャン [Object Copy]:Evacuation、退避処理 [Termination]:他スレッド処理を steal して処理した時間 [GC Worker Other]:処理時間に計上されない内部処理 [GC Worker Total]:Start から End までの時間 [GC Worker End]:終了タイムスタンプ (VM起動時間)
49. 49. [GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] Copyright©2015 NTT corp. All Rights Reserved. 49 ログと大まかな処理の流れ オブジェクト情報を保持する構造の掃除など [Code Root Fixup: X ms] [Code Root Purge: X ms] [Clear CT: X ms]
50. 50. Copyright©2015 NTT corp. All Rights Reserved. 50 ログと大まかな処理の流れ[GC pause (G1 Evacuation Pause) (young), 0.0650323 secs] [Parallel Time: 38.6 ms, GC Workers: 10] [GC Worker Start (ms): Min: 27181.9, Avg: 27182.2, Max: 27184.0, Diff: 2.1] [Ext Root Scanning (ms): Min: 0.0, Avg: 0.9, Max: 1.9, Diff: 1.9, Sum: 8.8] [Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 1.1] [Processed Buffers: Min: 0, Avg: 0.8, Max: 3, Diff: 3, Sum: 8] [Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3] [Code Root Scanning (ms): Min: 0.5, Avg: 1.0, Max: 1.8, Diff: 1.2, Sum: 9.7] [Object Copy (ms): Min: 15.2, Avg: 16.6, Max: 17.4, Diff: 2.3, Sum: 166.0] [Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 2.4] [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4] [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.3] [GC Worker Total (ms): Min: 17.0, Avg: 18.9, Max: 19.1, Diff: 2.1, Sum: 188.6] [GC Worker End (ms): Min: 27201.0, Avg: 27201.0, Max: 27201.0, Diff: 0.0] [Code Root Fixup: 1.0 ms] [Code Root Purge: 0.1 ms] [Clear CT: 1.4 ms] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] [Eden: 224.0M(224.0M)->0.0B(196.0M) Survivors: 0.0B->28.0M Heap: 228.9M(4500.0M)->48.5M(4500.0M)] [Times: user=0.26 sys=0.08, real=0.06 secs] [Other: 23.9 ms] [Choose CSet: 0.0 ms] [Ref Proc: 21.4 ms] [Ref Enq: 0.2 ms] [Redirty Cards: 1.2 ms] [Humongous Register: 0.0 ms] [Humongous Reclaim: 0.0 ms] [Free CSet: 0.4 ms] それ以外の処理 GC対象Regionセット収集 強参照以外の処理と収集 Dirty Card の再処理 Humongousの 処理と解放 GC対象Regionセットの解放
51. 51. Copyright©2015 NTT corp. All Rights Reserved. 51 Young GC 後 O S S S O O H Young GC 編おしまい 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
52. 52. Copyright©2015 NTT corp. All Rights Reserved. 52 複数回の Young GC 後 O S O O O O S S Heap の使用率が閾値を超えると Marking Cycle が発生 O O O O O O E E E E H O 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
53. 53. Copyright©2015 NTT corp. All Rights Reserved. 53 Marking Cycle O O S O O O O S S Heap の使用率が閾値を超えると Marking Cycle が発生 O O O O O O E E E E HYoung GC or Humongous 配置後のヒープ 使用率がデフォルトで 45% 超えると発生 -XX:InitiatingHeapOccupancyPercent で設定可 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
54. 54. Copyright©2015 NTT corp. All Rights Reserved. 54 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] Marking Cycle のログ全容 (ラベルで判断)
55. 55. Copyright©2015 NTT corp. All Rights Reserved. 55 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] マーキングサイクルの開始
56. 56. Copyright©2015 NTT corp. All Rights Reserved. 56 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] Root Region を決定 (initial-mark)
57. 57. Copyright©2015 NTT corp. All Rights Reserved. 57 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] Root Region をスキャン (concurrent-root-region-scan)
58. 58. Copyright©2015 NTT corp. All Rights Reserved. 58 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] 参照を辿ってマーク (concurrent-mark)
59. 59. Copyright©2015 NTT corp. All Rights Reserved. 59 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] 漏れを防ぐために全スレッド止めて再マーク
60. 60. Copyright©2015 NTT corp. All Rights Reserved. 60 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC のログがここに入るケースが多い) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] 漏れを防ぐために全スレッド止めて再マーク Finalize Marking: 強参照の再マーク GC ref-proc: 強参照「以外」のマーク Unloading: クラスアンロード処理
61. 61. Copyright©2015 NTT corp. All Rights Reserved. 61 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] 生存オブジェクトのない Region 回収など
62. 62. Copyright©2015 NTT corp. All Rights Reserved. 62 Marking Cycle ログ [GC pause (<GCCause>) (young) (initial-mark), 0.00554820 secs] ：(Young GC のログ) → 最後に [Times:… real=X.XX secs] [GC concurrent-root-region-scan-start] [GC concurrent-root-region-scan-end, 0.0566056 secs] [GC concurrent-mark-start] ：(0 以上の Young GC が発生する) [GC concurrent-mark-end, 1.6776461 secs] [GC remark [Finalize Marking, 0.0000801 secs] [GC ref-proc, 0.0000749 secs] [Unloading, 0.0007663 secs], 0.0010696 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC cleanup 16G->14G(32G), 0.0557430 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC concurrent-cleanup-start] [GC concurrent-cleanup-end, 0.0222541 secs] Concurrent ではない処理は STW が発生する
63. 63. Copyright©2015 NTT corp. All Rights Reserved. 63 Marking Cycle 後 参照追跡を完了し、各 Region ごとの生存オ ブジェクト情報を得て Mixed GC を起動 O O S O O O O S S O O O O O O E E E E H 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
64. 64. Copyright©2015 NTT corp. All Rights Reserved. 64 Mixed GC O O S O O O O S S O O O O O O E E E E H アルゴリズム(とログ)は Young GC と一緒 [GC pause (G1 Evacuation Pause) (mixed), 0.0640122 secs] GC発生原因(GC Cause) ここが mixed になるだけ 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
65. 65. Copyright©2015 NTT corp. All Rights Reserved. 65 Mixed GC と Young GC の違い O O S O O O O S S O O O O O O E E E E H JDK-8059452 でデフォルト値が変更 ゴミが多い Region を対象に GC する ・全ての Eden, Survivor と、不要オブジェクトが閾値 (デフォルト 85%) を上回る Old Region が GC 対象。 -XX:G1MixedGCLiveThresholdPercent で設定可能 条件達成まで複数回起動する ・回収可能な Old Regionの不要オブジェクトが、ヒー プ全体の閾値(デフォルト 5%)以下になるまで繰り返 す。-XX:G1HeapWastePercent で設定可能 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
66. 66. Copyright©2015 NTT corp. All Rights Reserved. 66 Mixed GC O O S O O O O S S O O O O O O E E E E H 全ての Eden, Survivor から新たな Survivor、 選択された Old から新たな Old へ退避する 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
67. 67. Copyright©2015 NTT corp. All Rights Reserved. 67 Mixed GC 全ての Eden, Survivor から新たな Survivor、 選択された Old から新たな Old へ退避する O O S O O O O S S O O O O O O E E E E H O 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
68. 68. Copyright©2015 NTT corp. All Rights Reserved. 68 Mixed GC 全ての Eden, Survivor から新たな Survivor、 選択された Old から新たな Old へ退避する O O S O S S S O O O O S S O O O O O O E E E E H O 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
69. 69. Copyright©2015 NTT corp. All Rights Reserved. 69 Mixed GC 後 O S O S S O O O O O O O O O O H 退避元 Eden, Survivor, Old の Region を回収 条件達成してなければ次の Mixed GC へ 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
70. 70. Copyright©2015 NTT corp. All Rights Reserved. 70 Mixed GC 停止後 S S O O O S O O O O O O H 最終的にゴミが多かった Old Region が 全て回収されて Mixed GC が停止する 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
71. 71. まとめ Copyright©2015 NTT corp. All Rights Reserved. 71 • Young GC と Mixed GC –アルゴリズム(とログ)は一緒 –大きな違いは GC 対象の Region –Regionごとの退避と解放の繰り返し • Marking Cycle –対象 Region を決めるのに必要な処 理を一部コンカレントに行っている ログもインデントのおかげで慣れると楽です
72. 72. 注意すべき パターン 汎用的なチューニング指南 Copyright©2015 NTT corp. All Rights Reserved. 72
73. 73. Copyright©2015 NTT corp. All Rights Reserved. 73 Evacuation Failure E S E S E S E O O S H O 退避 (Evacuation) 先の Survivor or Old に 退避させるスペースがなく失敗したパターン Full GC が起動する場合もある 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
74. 74. Copyright©2015 NTT corp. All Rights Reserved. 74 Evacuation Failure E S E S E S E O O S H O ログには (to-space exhausted) と出ます 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用[GC pause (G1 Evacuation Pause) (mixed) (to-space exhausted), 0.0083907 secs] [Parallel Time: 11.7 ms, GC Workers: 10] :
75. 75. Copyright©2015 NTT corp. All Rights Reserved. 75 Evacuation Failure E S E S E S E O O S H O Full GC が起動した場合でも同じです 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用[GC pause (G1 Evacuation Pause) (mixed) (to-space exhausted), 0.0083907 secs] [Parallel Time: 11.7 ms, GC Workers: 10] : [GC pause (G1 Evacuation Pause) (young) (initial-mark) (to-space exhausted), 0.0045139 secs] : [GC concurrent-mark-start] [Full GC (Allocation Failure) 4429M->113M(4500M), 0.7380897 secs] [Eden: 0.0B(224.0M)->0.0B(2004.0M) Survivors: 0.0B->0.0B Heap: 4429.1M(4500.0M)->113.1M(4500.0M)], [Metaspace: 12003K->12003K(1060864K)] [Times: user=0.78 sys=0.00, real=0.73 secs] [GC concurrent-mark-abort] :
76. 76. 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用 Copyright©2015 NTT corp. All Rights Reserved. 76 Evacuation Failure E S E S E S E O O S H O [GC pause (G1 Evacuation Pause) (mixed) (to-space exhausted), 0.0083907 secs] [Parallel Time: 11.7 ms, GC Workers: 10] : [GC pause (G1 Evacuation Pause) (young) (initial-mark) (to-space exhausted), 0.0045139 secs] : [GC concurrent-mark-start] [Full GC (Allocation Failure) 4429M->113M(4500M), 0.7380897 secs] [Eden: 0.0B(224.0M)->0.0B(2004.0M) Survivors: 0.0B->0.0B Heap: 4429.1M(4500.0M)->113.1M(4500.0M)], [Metaspace: 12003K->12003K(1060864K)] [Times: user=0.78 sys=0.00, real=0.73 secs] [GC concurrent-mark-abort] : 実 STW 時間 Full GC のログもこれまでと同じ形式です 各空間の GC前後の 使用量(容量) GC Cause
77. 77. 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用 Copyright©2015 NTT corp. All Rights Reserved. 77 Evacuation Failure E S E S E S E O O S H O [GC pause (G1 Evacuation Pause) (mixed) (to-space exhausted), 0.0083907 secs] [Parallel Time: 11.7 ms, GC Workers: 10] : [GC pause (G1 Evacuation Pause) (young) (initial-mark) (to-space exhausted), 0.0045139 secs] : [GC concurrent-mark-start] [Full GC (Allocation Failure) 4429M->113M(4500M), 0.7380897 secs] [Eden: 0.0B(224.0M)->0.0B(2004.0M) Survivors: 0.0B->0.0B Heap: 4429.1M(4500.0M)->113.1M(4500.0M)], [Metaspace: 12003K->12003K(1060864K)] [Times: user=0.78 sys=0.00, real=0.73 secs] [GC concurrent-mark-abort] : 実 STW 時間 各空間の GC前後の 使用量(容量) GC Cause対策案 1. Heap を増やす (Region の個数を増やす) 2. -XX:InitiatingHeapOccupancyPercent を 下げてサイクル頻度を上げる 3. -Xms, -Xmx, -XX:MaxGCPauseMillis 以外を 削除し、over-tuning を回避する Region 管理の改善が代表的な対策です
78. 78. Copyright©2015 NTT corp. All Rights Reserved. 78 Humongous Allocation 頻発 E S H H E S E H S H E O O S H O H Humongous Object が大量に生成され、 GC 頻発や処理に時間が懸かるパターン 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
79. 79. Copyright©2015 NTT corp. All Rights Reserved. 79 Humongous Allocation 頻発 E S H H E S E H S H E O O S H O H [GC pause (G1 Humongous Allocation) (mixed), 0.4331340 secs] : [Other: 0.7 ms] [Choose CSet: 0.0 ms] [Ref Proc: 0.2 ms] [Ref Enq: 0.0 ms] [Redirty Cards: 0.2 ms] [Humongous Register: 260.1 ms] [Humongous Reclaim: 480.7 ms] [Free CSet: 0.1 ms] : GC Cause が G1 Humongous Allocation の GC Pause や、Humongous 関連処理の 処理時間から確認します 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
80. 80. Copyright©2015 NTT corp. All Rights Reserved. 80 Humongous Allocation 頻発 E S H H E S E H S H E O O S H O H [GC pause (G1 Humongous Allocation) (mixed), 0.4331340 secs] : [Other: 0.7 ms] [Choose CSet: 0.0 ms] [Ref Proc: 0.2 ms] [Ref Enq: 0.0 ms] [Redirty Cards: 0.2 ms] [Humongous Register: 260.1 ms] [Humongous Reclaim: 480.7 ms] [Free CSet: 0.1 ms] : 対策案 1. -XX:G1HeapRegionSize で Region サイズ を Heap と一緒に増やす。Heap を増やさ ない場合は Region 数が減り Evacuation Failure の可能性が増すので注意 2. 巨大なオブジェクトを極力生成しない (長大な配列、文字列、フィールド数が極 端にクラスなど) Humongous を減らすのが抜本対策 水:Eden 橙:Survivor 緑:Old 紫:Humongous 藍:未使用
81. 81. Copyright©2015 NTT corp. All Rights Reserved. 81 CPU 処理時間が長い Java プロセス以外にも疑うべき範囲が 広がりますが、GC 処理時間が長いパターン [GC pause (G1 Evacuation Pause) (mixed), 0.8332274 secs] : [Ref Proc: 103.4 ms] : [Times: user=1.25 sys=0.60, real=0.83 secs]
82. 82. Copyright©2015 NTT corp. All Rights Reserved. 82 CPU 処理時間が長い [GC pause (G1 Evacuation Pause) (mixed), 0.8332274 secs] : [Ref Proc: 103.4 ms] : [Times: user=1.25 sys=0.60, real=0.83 secs] 対策案 1. 物理 CPU コアが余裕なら -XX:ConcGCThreads を増や して並列度を上げる。逆にコア数が少ない、メモリが 小さい場合は、従来GCを検討する 2. Reference Processing([Ref Proc]) の時間が長い場合は、 -XX:+ParallelRefProcEnabled を指定して並列処理する。 WeakReference や SoftReference の抑制も検討する 3. -XX:InitiatingHeapOccupancyPercent を上げてサイク ル頻度を下げる (副作用もあるので注意) 特にケースバイケースなパターンなので注意
83. 83. まとめ Copyright©2015 NTT corp. All Rights Reserved. 83 • Evacuation Failure –ヒープを増やそう • Humongous Allocation –ヒープを増やそう • CPU 処理時間が長い –CPUを増やそう(NUMA環境は注意) ジョークですが G1 が生まれた経緯はこれ
84. 84. おわりに Copyright©2015 NTT corp. All Rights Reserved. 84 • 自分のアプリケーションがどの ようにメモリを使っているかは 意識しましょう • まずは動かして性能を測定して みてください • GC に任せるのはそれから 現場に神宿る
85. 85. References Copyright©2015 NTT corp. All Rights Reserved. 85 • Detlefs, D., Flood, C., Heller, S., and Printezis, T. “Garbage-first garbage collection” (ISMM 2004) • http://hg.openjdk.java.net/jdk8u/ • jdk8u-dev/hotspot (7664:831754f092fb) • Getting Started with G1 Garbage Collector (Oracle Documents) HeapStats チームや同僚達の支えに感謝
86. 86. End おつかれさまでした Copyright©2015 NTT corp. All Rights Reserved. 86