김명식 / Embedded Software Systems Lab.

Division of Computer Science & Engineering

Hanyang University

SQLite의 입출력 특성분석: Android 와 Tizen 사례

1. IntroductionSQLite in Mobile Platform

2. Analysis Analysis MethodExperiment Setup

3. ResultI/O Semantics (Size Distribution, Block Type, File Type)Tracing I/O on Database workload

4. DiscussionFilesystem journaling SQLite journal mode Platform DB usageOptimization Approaches

5. Conclusion

CONTENTS

1. Introduction

SQLite in Mobile Platform

1. Introduction

SQLite in Mobile Platform

What is SQLite스마트폰을 비롯한 다수 임베디드 장비에서 사용되고 있는 경량 DBMS 라이브러리

• Open Source , Support multiple OS’s

• Support Structured Query Language (SQL)

• ACID Compliant (Atomicity, Consistency, Isolation, Durability)

• Zero configuration

Mobile Platform 및 어플리케이션에서는 주로 SQLite를 사용해 DB 형태로 데이터를 저장

• The database is stored in the /data/data/<package>/databases folder

• Android OS version 및 제조사에 따라 탑재 SQLite 차이• < 2.1 : SQLite 3.5.9

• 2.2 - 2.3.3 : SQlite 3.6.22

• 3.0 ­ 4.0.3 : SQLite 3.7.4

• 4.1 ­ 4.2.x : SQLite 3.7.11

• 4.4.x : SQLite 3.7.13

• Latest SQLite Version: 3.8.5

SQLite in Mobile Platform

대부분 Mobile Platform에서 SQLite 사용Android, Tizen, iOS 다수의 Embedded Mobile Platform 에서 Sqlite를 사용

App 뿐만 아니라 Webkit과 같은 Platform 의 Framework 요소도 Sqlite 접근

SQLite in Mobile Platform

SQLiteSQLite

SQLiteSQLite

1. Introduction

SQLite in Mobile Platform

2. Analysis Analysis MethodExperiment Setup

IO Analysis Approach

User Domain

Kernel Domain

MobilePlatform

Linuxkernel

Mobile Applications

?

Core

Web Framework Native Framework

Native App Web App Hybrid App

Storage

SQLiteSQLite

MOST (Mobile Storage Analyzer) A tool for collecting IO attributes across layers

blktrace+α for tracing in real-time, debugfs+β for post reverse-mapping

IO Analysis Approach

2. LBA-to-file mapping

3. LBA-to-Process mapping

1. BLOCK IO Tracing

File systemFile system

Block I/OBlock I/O

ApplicationApplication

Specification of Evaluation Mobile

RD-PQ ( Tizen ) & Galaxy S3 (Android)

Workload & Filetype

File type Extension nameExecutable apk, tpkc, wgtd, exe, so

SQLite SQLite DB (.db)SQLite-temp SQLite-temp(.db-journal .db-wal .db-shm)Multimedia mp4, jpg, mp3, png, etcResources dat, xml, js, cache, etc

Others Others including directory entryc Tizen native app package ( tpk), d Tizen web app package ( wgt)

• Six file groups

Name (abbreviation) ScenarioContact1 (Cn1), Contact2 (Cn2) Adding name and dial number at contact list

Google (Br1), Daum (Br2), Naver (Br3) News reading, web searching from Website

Mail (Ml) Updating mailbox, Read and reply a mail

Camera (C), Camcorder (Cc) Take a picture, record movie

Media (Me), Music (Mus), Gallery (Gal) Play movie, music, image in localstorage

Youtube (You) Play web-streaming movie on youtube

Fishbowl (Fsb), Game (Gam) Browsing HTML5 Webapp benchmark site

• 14 scenarios on 7 applications

1. Introduction

SQLite in Mobile Platform

3. Result

IO Semantics (Size Distribution, Block Type, File Type)Locality, Buffered vs Synchronous Write

IO Semantics Sub-Type Tizen Android

IO Size IO Size 4KB 45% 65%

Block type Size D>J>M D>J>M

Popular large extent 128K 512K

Block type Meta and Journal 66.4(count) 57(size) 45.1(count) 37.3(size)

File type Sqlite and Sqlitetemp 75(count)54(size) 47.6(count) 40.2(size)

Sequentially Random count / Sequential Size

86 / 78 81.4 / 78

Buffered Write Sync WS 90 51.8

IO Semantics

SQLite and SQLite-temp write are dominant

Q&A

IO Size4K size 가 주요함, 안드로이드가 좀 더 높은 4K 비율

IO Blocktype실제 Data 못지 않게 저널과 메타가 비중이 높다

IO Filetype두 플랫폼 공통적으로 SQLite 관련 IO가 주요 비중

IO Sequentially횟수 측면에서는 Random IO, 크기는 Sequential IO가 주요

IO ProcessWrite Sync 가 주요, Android 는 Buffered Write 활용도 높음

I/O characteristics of Mobile Platform

To protect power failures

Generates small random, large sequential

Metadata and Journal are dominant

DB transactionis dominant

4KB is dominant

SQLite Journaling mode

SQLite Journaling Mode DELETE TRUNCATE PERSIST WAL

Number of fsync() calls 2 2 3 1

Number of IOs 9 8 12 3

EXT4 Journal size (metadata) 24 KB 16 KB 8 KB 16 KB

Total IO Volume 72 KB 64 KB 72 KB 36 KB

DELETE TRUNCATE

PERSIST WAL

Reference : Sooman Jeong et al. “I/O Stack Optimization for smartphones” USENIX ATC'13, SAN JOSE, CA, June 26~28, 2013Tizen use

Journal Mode

동작 적용 단말

ROLLBACK

DELETE

Transaction 마다 Journal file을 생성, 삭제함 GALAXY S Gingerbread, Linux Kernel 2.6.35.7

생성, 삭제하는 overhead가 큼.

TRUNCATEJournal file을 삭제하는 대신에, file size를 0으로 만듦. GALAXY S3 IceCream,

Linux Kernel 3.0 수정 사항이 Journal file에 append 되므로 delete 보다 개선

PERSIST

Journal file을 삭제하지 않고, size도 변경하지 않음. Journal header를 0으로 채움.

Tizen magnolia 2.2.1, Linux Kernel 3.0

수정 사항이 Append 되지 않고, existing block에 적용되어 TRUNCATE 보다 좀 더 성능 향상이 됨.

WAL WAL

Db의 복사본인 저널은 생성 하지 않고 메타 정보인 Wal 파일을 생성하여, 수정 사항을 Wal 파일에 sequential하게 append 함.

GALAXY S3 Jellybean 4.1.2Linux Kernel 3.0.31

수정 사항이 특정 threshold 까지 계속 sequential 하게 write 됨. 대부분의 scenario에서 성능 향상

SQLite Journaling mode

SQLite IO Pattern

2 fsync() and 8 writes in Android

3 fsync() and 12 writes in Tizen

Directory fsync()Directory fsync()

SQLite IO Pattern

Media.db

Meta of Foo.jpg

Media.db

• Before-and-after Binary Comparison when insert 1 record in media.db

• 사진 촬영 시 촬영된 사진 파일의 각종 메타 정보가 media.db에 추가됨

• MOST로 분석, 동작 전후의 db file의 binary Diff 하여 분석

• 다수회의 DB Transaction 이 조합되어 관찰됨

Foo.jpg

SQLite IO Pattern in Mobile Platform

Media.db

Media table in Media.db

Media table in Media.db

Media table in Media.db

Media table in Media.db

Iu.upload.dbAndroid 도 Tizen media.db와 유사한iu.upload.db 사용 (media record table, 29 field)

Q&A

■ B-Tree 구조를 가지고 Page 구조들 간 연결 되어 있음

■ Page (4KB) 내부는 Cell offset과 Cell로 구성

■ Cell Offset은 Page 선두에 위치, Cell 은 heap 처럼 Page 끝에서 부터 자라 올라옴

■ 각 Cell은 Cell Size/ID로 구성된 Cell Header와 Cell Size 만큼에 실제 Record header/Data 가 위치함.

SQLite File StructureFile signiture : 0x53 51 4c 69 74 65 20 66 6f 72 6d 61 74 20 33 00 (16 bytes).Page Size Definition: 4096 (0x10 00, big endian) Schema Table

DB Header

Schema Table

Pages

B-TreeTableN..

Pages

Page 1

B-TreeTable

index b-tree (index)Table b-tree (Contents)

....

Pages

Page header StructurePage Header

Offset 0

Cell 0

Offset 1

Cell 1

....

DB header Structure

Ref. 안랩 온라인 보안 매거진 월간 안(2014.04~ 2014.07)

Under 10 byte 27회

Under 100byte13회

More 400 bytes8회(shifting)

DB Binary Diff in a transaction

380 Bytes insert to the table in media.db

Media.db + media.db-journal + ext4 padding data

380 Bytes 132 KBx350 WAF

Update DB withBinary Shifting,fragmentation

380 Bytes 396 KBx1067 WAF

Media.db Only

Effect of DB transaction

eMMC Device

JEDEC mode (HS200, 400, UFS)

Block IO

IO Scheduler

Ext4 Filesystem

Data Journaling, Metadata

SQLite Library

Generation .db file DB journaling

Platform

DB for platform DB for manufacturer, carrier

App

DB for application DB from Web Access

DB insert

.db file .db-journal file

journal meta data journal meta data

DB transaction makesfacilitated diffusion of IO

DB Generates Excessive I/O

Flash MemoryDatabase DataOpen DB files(.db or .db-journal)

File System

Ext4 journalwrite() , fsync()

Insert a name,phone number

Adding one contacts generates 560 KB write traffic

2번의 journal fsync , 1번의 fsync, 1번의 journal fsync로구성

하나의 이름,전화번호 저장에 총 IO 580KB 발생

총 .contacts-svc.db에 3회의 db file fsync와 9회의 journal file fsync발생

1. Introduction

SQLite in Mobile Platform

4. Discussion

Filesystem journaling SQLite journal mode Platform DB usageOptimization Approaches

Q&A

수명

쓰기 내구성에 한계가 있는 낸드 플래시의 수명에 악 영향

성능

애플리케이션들이 발생시키는 DB 쓰기는 과도한 저널링 부하 생성

DB의 저널 파일을 파일 시스템에서 다시 저널링 하는 중복 저널 현상

사용자 앱/ 기기 제조사 /플랫폼의 유사 정보 중복 DB 접근

SQLite 연동시의 문제점

Q&A

Kernel 최적화Block I/O Scheduler

Page cache

Eliminating unnecessary metadata flushes using fdatasync()

Filesystem 최적화Ext4 mount option optimization (norelatime, Jounrnal_async_commit)

log-structured Filesystem : Flash friendly Filesystem (F2FS)

Discussion

fdatasync() for Metadata Flushes

fsync(fd0)

sizedata atimemtimedata

fsync(fd1) fdatasync(fd0)

sizedata atimemtimedata

fdatasync(fd1)

Page cache

Disk

Reference : Sooman Jeong et al. “I/O Stack Optimization for smartphones” USENIX ATC'13, SAN JOSE, CA, June 26~28, 2013

Fdatasync flush metadata only when file size changes

mtime = modify time, atime = access time

MetadataData

fsync()fsync() fdatasync()fdatasync()

fdatasync() for Metadata Flushes

size

data

data atimemtime dataPage cache

Disk

size

data data’ data’

mtime

fdatasync() fdatasync()

Why does fdatasync() brings more performance gain in update operation?

SQLite InsertSQLite Insert SQLite UpdateSQLite Update

Reference : Sooman Jeong et al. “I/O Stack Optimization for smartphones” USENIX ATC'13, SAN JOSE, CA, June 26~28, 2013

Q&A

SQLite 개선WAL 모드 적용

Multi-version B-tree(MVBT)의 적용, Tree 구조 개선을 통해 SQLite

transection 수행 시 update 되는 db-page 의 개수 최적화

Lazy Split, disabling sibling , Lazy Garbage Collection à Less fsync(),

Less dirty pages

Embedding Metadata, SQLite의 journal file 의 역할을 DB file로

embedding

WAL-mode 70%, Truncate mode 1,220% 향상.

Ref. KIM, W.-H., NAM, B., PARK, D., AND WON, Y. Resolving journaling of journal anomaly in android I/O: Multi-version

b-tree with lazy split. In Proceedings of the 12th USENIX Conference on File and Storage Technologies (FAST 14) (Santa

Clara, CA, 2014),USENIX, pp. 273­28

Discussion

Q&A

New Architecture No Journaling ( iOS HFS+)

Quisi-NVRAM (DRAM to act as a battery backed up nonvolatile DRAM.)

Discussion

Ref. Hao Luo, Lei Tian and Hong Jiang , qNVRAM: quasi Non-Volatile RAM for Low Overhead Persistency Enforcement in

Smartphones, University of Nebraska, Lincoln, Hotstorage 14, USENIX

Junghoon Kim; Changwoo Min; Young Eom, "Reducing excessive journaling overhead with small-sized NVRAM for mobile

devices," Consumer Electronics, IEEE Transactions on , vol.60, no.2, pp.217,224, May 2014

The Performance of Persistent Page Cache and LazyFlush

speeds up the insert, update and delete transactions by up to 16.33x, 15.86x and 15.76x respectively.

Q&A

Platform필요한 쓰기 접근인지 트랜잭션 처리에 따른 IO 비용이 높은 DB를 사용

해야 하는지 고민 필요

DB 사용 시 schema, index,

저널링 모드 Effective journaling mode is WAL.

플랫폼 / 제조사 / App 의 중복된 접근에 대한 최적화 필요

Reorganize Web Database

Discussion

Q&A

Data Persistency in Web

Webkit 도 다양한 DB 쓰기 접근이 관찰됨

Web Storage

Web SQL DB: deprecated

HTML5 localstorage

only store a simple key-value pairs

Indexed DB

Object store 를 만들고 object 를 저장

단순 Key-Value Storage, SQL Query 대신 javascript index 를 사용

Reorganize Web Database

Databases.db

Storagetracker.db

Reorganize Database Usage

icon.db

Reorganize Database Usage

Q&A

Explore SQLite DB IO characteristics in Mobile Platform

- SQLite DB IO is dominant in Mobile.

- Excessive journaling I/O caused by SQLite and Ext4

- Need to rethink DB usage, DB file structure

Conclusion

THANK YOU

Q&A