apweb’2011 tutorial

APWeb’2011 Tutorial

Jiaheng Lu and Sai WuRenmin Universtiy of China , National University of Singapore

Cloud Computing and Scalable Data Management

APWeb 2011

Cloud computing Map/Reduce, Bigtable and PNUT CAP Theorem and datalog Data indexing in the clouds Conclusion and open issues

Outline

Part 1

Part 2

Cloud computing

Why we use cloud computing?


Case 1:Write a fileSaveComputer down, file is lost

Files are always stored in cloud, never lost


Case 2:Use IE --- download, install, useUse QQ --- download, install, useUse C++ --- download, install, use……

Get the serve from the cloud

What is cloud and cloud computing?

Cloud computing is a style of computing in which dynamically scalable and often virtualized resources are provided as a serve over the Internet.

Users need not have knowledge of, expertise in, or control over the technology infrastructure in the "cloud" that supports them.

Characteristics of cloud computing

• Virtual. software, databases, Web servers,

operating systems, storage and networking as virtual servers.

• On demand. add and subtract processors, memory,

network bandwidth, storage.

IaaSInfrastructure as a Service

PaaSPlatform as a Service

SaaSSoftware as a Service

Types of cloud service

APWeb 2011


Outline

Part 1

Part 2

Introduction to Introduction to MapReduce MapReduce

MapReduce Programming ModelMapReduce Programming Model

• Inspired from map and reduce operations commonly

used in functional programming languages like Lisp.

• Users implement interface of two primary methods:–1. Map: (key1, val1) → (key2, val2)–2. Reduce: (key2, [val2]) → [val3]

Map operationMap operation • Map, a pure function, written by the user, takes an

input key/value pair and produces a set of intermediate key/value pairs. –e.g. (doc—id, doc-content)

• Draw an analogy to SQL, map can be visualized as group-by clause of an aggregate query.

Reduce operationReduce operation • On completion of map phase, all the

intermediate values for a given output key are combined together into a list and given to a reducer.

• Can be visualized as aggregate function (e.g., average) that is computed over all the rows with the same group-by attribute.

Pseudo-codePseudo-codemap(String input_key, String input_value): // input_key: document name // input_value: document contents

for each word w in input_value: EmitIntermediate(w, "1");

reduce(String output_key, Iterator intermediate_values): // output_key: a word // output_values: a list of counts

int result = 0; for each v in intermediate_values:

result += ParseInt(v); Emit(AsString(result));

MapReduce: Execution overviewMapReduce: Execution overview

MapReduce: ExampleMapReduce: Example

Research works

• MapReduce is slower than Parallel Databases by a factor 3.1 to 6.5 [1][2]

• By adopting an hybrid architecture, the performance of MapReduce can approach to Parallel Databases [3]

• MapReduce is an efficient tool [4]• Numerous discussions in MapReduce community …

[1] A comparison of approaches to large-scale data analysis. SIGMOD 2009[2] MapReduce and Parallel DBMSs: friends or foes? CACM 2010[3] HadoopDB: an architectural hybrid of MapReduce and DBMS techonologies for analytical workloads. VLDB 2009[4] MapReduce: a flexible data processing tool. CACM 2010

An in-depth study (1)

• Scheduling• I/O modes• Record Parsing• Indexing

A performance study of MapReduce (Hadoop) on a 100-node cluster of Amazon EC2 with various levels of parallelism. [5]

[5] Dawei Jiang, Beng Chin Ooi, Lei Shi, Sai Wu: The Performance of MapReduce: An In-depth Study. PVLDB 3(1): 472-483 (2010)

An in-depth study (2)

• By carefully tuning these factors, the overall performance of Hadoop can be comparable to that of parallel database systems.

• Possible to build a cloud data processing system that is both elastically scalable and efficient

[5] Dawei Jiang, Beng Chin Ooi, Lei Shi, Sai Wu: The Performance of MapReduce: An In-depth Study. PVLDB 3(1): 472-483 (2010)

Osprey: Implementing MapReduce-Style Fault Tolerance in a Shared-

Nothing Distributed Database

Christopher Yang, Christine Yen, Ceryen Tan, Samuel Madden: Osprey: Implementing MapReduce-style fault tolerance in a

shared-nothing distributed database. ICDE 2010:657-668

Problem proposed

• Problem: Node failures on distributed database system– Faults may be common on large clusters of machines

• Existing solution: Aborting and (possibly) restarting the query– A reasonable approach for short OLTP-style queries– But it’s time-wasting for analytical (OLAP) warehouse

queries

MapReduce-style fault tolerance for a SQL database

• Break up a SQL query (or program) into smaller, parallelizable subqueries

• Adapt the load balancing strategy of greedy assignment of work

Osprey

• A middleware implementation of MapReduce-style fault tolerance for a SQL database

SQL procedureQuery Query Transformer

SubquerySubquerySubquery

PWQ A

Scheduler

Result Merger Result

Execution


PWQ B


PWQ C

PWQ :partition work queue

Mapreduce Online Evaluation Plateform

Construction

23/4/1930School Of Information Renmin University Of China

Cloud data management

Four new principles in Cloud-based data management

New principle in cloud dta management （ 1 ）

• Partition Everything and key-value storage

• 切分万物以治之

•1st normal form cannot be satisfied


• Embrace Inconsistency

• 容不同乃成大同

•ACID properties are not satisfied


• Backup everything with three copies

• 狡兔三窟方高枕

• Guarantee 99.999999% safety


• Scalable and high performance

•运筹沧海量兼容

Cloud data management

•切分万物以治之•Partition Everything•容不同乃成大同•Embrace Inconsistency•狡兔三窟方高枕•Backup data with three copies•运筹沧海量兼容•Scalable and high performance

BigTable: A Distributed Storage System for Structured Data

Introduction

• BigTable is a distributed storage system for managing structured data.

• Designed to scale to a very large size– Petabytes of data across thousands of servers

• Used for many Google projects– Web indexing, Personalized Search, Google Earth, Google

Analytics, Google Finance, …

• Flexible, high-performance solution for all of Google’s products

Why not just use commercial DB?

• Scale is too large for most commercial databases• Even if it weren’t, cost would be very high

– Building internally means system can be applied across many projects for low incremental cost

• Low-level storage optimizations help performance significantly– Much harder to do when running on top of a database

layer

Goals

• Want asynchronous processes to be continuously updating different pieces of data– Want access to most current data at any time

• Need to support:– Very high read/write rates (millions of ops per second)– Efficient scans over all or interesting subsets of data– Efficient joins of large one-to-one and one-to-many

datasets• Often want to examine data changes over time

– E.g. Contents of a web page over multiple crawls

BigTable

• Distributed multi-level map• Fault-tolerant, persistent• Scalable

– Thousands of servers– Terabytes of in-memory data– Petabyte of disk-based data– Millions of reads/writes per second, efficient scans

• Self-managing– Servers can be added/removed dynamically– Servers adjust to load imbalance

Basic Data Model

• A BigTable is a sparse, distributed persistent multi-dimensional sorted map

(row, column, timestamp) -> cell contents

• Good match for most Google applications

WebTable Example

• Want to keep copy of a large collection of web pages and related information

• Use URLs as row keys• Various aspects of web page as column names• Store contents of web pages in the contents: column

under the timestamps when they were fetched.

Rows

• Name is an arbitrary string– Access to data in a row is atomic– Row creation is implicit upon storing data

• Rows ordered lexicographically– Rows close together lexicographically usually on

one or a small number of machines

Rows (cont.)

Reads of short row ranges are efficient and typically require communication with a small number of machines.

• Can exploit this property by selecting row keys so they get good locality for data access.

• Example: math.gatech.edu, math.uga.edu, phys.gatech.edu, phys.uga.edu

VS

edu.gatech.math, edu.gatech.phys, edu.uga.math, edu.uga.phys

Columns

• Columns have two-level name structure:• family:optional_qualifier

• Column family– Unit of access control– Has associated type information

• Qualifier gives unbounded columns– Additional levels of indexing, if desired

Timestamps

• Used to store different versions of data in a cell– New writes default to current time, but timestamps for writes can also be set

explicitly by clients• Lookup options:

– “Return most recent K values”– “Return all values in timestamp range (or all values)”

• Column families can be marked w/ attributes:– “Only retain most recent K values in a cell”– “Keep values until they are older than K seconds”

Implementation – Three Major Components

• Library linked into every client• One master server

– Responsible for:• Assigning tablets to tablet servers• Detecting addition and expiration of tablet servers• Balancing tablet-server load• Garbage collection

• Many tablet servers– Tablet servers handle read and write requests to its table– Splits tablets that have grown too large

Tablets

• Large tables broken into tablets at row boundaries– Tablet holds contiguous range of rows

• Clients can often choose row keys to achieve locality– Aim for ~100MB to 200MB of data per tablet

• Serving machine responsible for ~100 tablets– Fast recovery:

• 100 machines each pick up 1 tablet for failed machine– Fine-grained load balancing:

• Migrate tablets away from overloaded machine• Master makes load-balancing decisions

Refinements: Locality Groups

• Can group multiple column families into a locality group– Separate SSTable is created for each locality group

in each tablet.• Segregating columns families that are not

typically accessed together enables more efficient reads.– In WebTable, page metadata can be in one group

and contents of the page in another group.

Refinements: Compression

• Many opportunities for compression– Similar values in the same row/column at different

timestamps– Similar values in different columns– Similar values across adjacent rows

• Two-pass custom compressions scheme– First pass: compress long common strings across a large

window– Second pass: look for repetitions in small window

• Speed emphasized, but good space reduction (10-to-1)

Refinements: Bloom Filters

• Read operation has to read from disk when desired SSTable isn’t in memory

• Reduce number of accesses by specifying a Bloom filter.– Allows us ask if an SSTable might contain data for a

specified row/column pair.– Small amount of memory for Bloom filters drastically

reduces the number of disk seeks for read operations– Use implies that most lookups for non-existent rows or

columns do not need to touch disk

PNUTS /

SHERPA

To Help You Scale Your Mountains of Data

Yahoo! Serving Storage Problem

– Small records – 100KB or less

– Structured records – lots of fields, evolving

– Extreme data scale - Tens of TB

– Extreme request scale - Tens of thousands of requests/sec

– Low latency globally - 20+ datacenters worldwide

– High Availability - outages cost $millions

– Variable usage patterns - as applications and users change

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E 75656 C

A 42342 EB 42521 W

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D 12352 E

F 15677 E

What is PNUTS/Sherpa?

E 75656 C

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C 66354 W

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CREATE TABLE Parts (ID VARCHAR,StockNumber INT,Status VARCHAR…

)

CREATE TABLE Parts (ID VARCHAR,StockNumber INT,Status VARCHAR…

)

Parallel databaseParallel database Geographic replicationGeographic replication

Structured, flexible schemaStructured, flexible schema

Hosted, managed infrastructureHosted, managed infrastructure

A 42342 E

B 42521 W

C 66354 W

D 12352 E

E 75656 C

F 15677 E

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What Will It Become?

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F 15677 E

E 75656 C

A 42342 EB 42521 W

C 66354 W

D 12352 E

F 15677 E

E 75656 C

A 42342 EB 42521 W

C 66354 W

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Indexes and viewsIndexes and views

Technology Elements

PNUTS • Query planning and execution• Index maintenance

Distributed infrastructure for tabular data • Data partitioning • Update consistency• Replication

YDOT FS • Ordered tables

Applications

Tribble• Pub/sub messaging

YDHT FS • Hash tables

Zookeeper• Consistency service

YC

A:

Aut

hori

zati

on

PNUTS API Tabular API

59

Data Manipulation

• Per-record operations– Get– Set– Delete

• Multi-record operations– Multiget– Scan– Getrange

60

Tablets—Hash Table

Apple

Lemon

Grape

Orange

Lime

Strawberry

Kiwi

Avocado

Tomato

Banana

Grapes are good to eat

Limes are green

Apple is wisdom

Strawberry shortcake

Arrgh! Don’t get scurvy!

But at what price?

How much did you pay for this lemon?

Is this a vegetable?

New Zealand

The perfect fruit

Name Description Price

$12

$9

$1

$900

$2

$3

$1

$14

$2

$8

0x0000

0xFFFF

0x911F

0x2AF3

61

Tablets—Ordered Table

62

Apple

Banana

Grape

Orange

Lime

Strawberry

Kiwi

Avocado

Tomato

Lemon

Grapes are good to eat

Limes are green

Apple is wisdom

Strawberry shortcake

Arrgh! Don’t get scurvy!

But at what price?

The perfect fruit

Is this a vegetable?

How much did you pay for this lemon?

New Zealand

$1

$3

$2

$12

$8

$1

$9

$2

$900

$14

Name Description PriceA

Z

Q

H

Flexible Schema

Posted date Listing id Item Price

6/1/07 424252 Couch $570

6/1/07 763245 Bike $86

6/3/07 211242 Car $1123

6/5/07 421133 Lamp $15

Color

Red

Condition

Good

Fair

Storageunits

Routers

Tablet Controller

REST API

Clients

Local region Remote regions

Tribble

Detailed Architecture

64

Tablet Splitting and Balancing

65

Each storage unit has many tablets (horizontal partitions of the table)Each storage unit has many tablets (horizontal partitions of the table)

Tablets may grow over timeTablets may grow over timeOverfull tablets splitOverfull tablets split

Storage unit may become a hotspotStorage unit may become a hotspot

Shed load by moving tablets to other serversShed load by moving tablets to other servers

Storage unitTablet

QUERY PROCESSING

66

Accessing Data

67

SUSU SU

1

Get key k

2Get key k3 Record for key k

4 Record for key k

Bulk Read

68

SUScatter/gather server

SU SU

1

{k1, k2, … kn}

2Get k1

Get k2Get k3

Storage unit 1 Storage unit 2 Storage unit 3

Range Queries in YDOT

• Clustered, ordered retrieval of records

Storage unit 1Canteloupe

Storage unit 3Lime

Storage unit 2Strawberry

Storage unit 1

Router

AppleAvocadoBananaBlueberry

CanteloupeGrapeKiwiLemon

LimeMangoOrange

StrawberryTomatoWatermelon

AppleAvocadoBananaBlueberry

CanteloupeGrapeKiwiLemon

LimeMangoOrange

StrawberryTomatoWatermelon

Grapefruit…Pear?Grapefruit…Lime?

Lime…Pear?

Storage unit 1Canteloupe

Storage unit 3Lime

Storage unit 2Strawberry

Storage unit 1

Updates

1

Write key k

2Write key k7

Sequence # for key k

8

Sequence # for key k

SU SU SU

3Write key k

4

5SUCCESS

6Write key k

RoutersMessage brokers

70

SHERPAIN CONTEXT

71

Types of Record Stores

• Query expressiveness

Simple Feature rich

Object retrieval

Retrieval from single table of

objects/records

SQL

S3 PNUTS Oracle


• Consistency model

Best effort Strong guaranteesEventual

consistencyTimeline

consistencyACID

S3 PNUTS Oracle

Program centric

consistency

Program centric

consistencyObject-centric consistency

Object-centric consistency


• Data model

Flexibility,Schema evolution

Optimized forFixed schemas

CouchDB

PNUTS

Oracle

Consistency spans objectsConsistency

spans objectsObject-centric consistency

Object-centric consistency


• Elasticity (ability to add resources on demand)

Inelastic Elastic

Limited (via data

distribution)

VLSD(Very Large

Scale Distribution /Replication)

OraclePNUTS

S3

Application Design Space

Records Files

Get a few things

Scan everything

Sherpa MObStor

Everest Hadoop

YMDBMySQL

Filer

Oracle

BigTable

76

Alternatives Matrix

Ela

stic

Ope

rabi

lity

Glo

bal l

ow

late

ncy

Ava

ilab

ilit

y

Stru

ctur

ed

acce

ss

Sherpa

Y! UDB

MySQL

Oracle

HDFS

BigTable

DynamoU

pdat

esCassandra

Con

sist

ency

m

odel

SQL

/AC

ID

77

APWeb 2011


Outline

Part 1

Part 2

The CAP Theorem

Consistency

Partition tolerance

Availability

The CAP Theorem

Once a writer has written, all readers will see that write

Consistency

Partition tolerance

Availability

The CAP Theorem

System is available during software and hardware upgrades and node failures.

Consistency

Partition tolerance

Availability

The CAP Theorem

A system can continue to operate in the presence of a network partitions.

Consistency

Partition tolerance

Availability

The CAP Theorem

Theorem: You can have at most two of these properties for any shared-data system

Consistency

Partition tolerance

Availability

Consistency

• Two kinds of consistency:– strong consistency – ACID(Atomicity Consistency Isolation

Durability)

– weak consistency – BASE(Basically Available Soft-state Eventual consistency )

A tailor

3NFTRANSACTION

LOCK ACID

SAFETY

RDBMS

Datalog

• Main expressive advantage: recursive queries.

• More convenient for analysis: papers look better.

• Without recursion but with negation it is equivalent in power to relational algebra

• Has affected real practice: (e.g., recursion in SQL3, magic sets transformations).

Datalog

• Example Datalog program:• parent(bill,mary). parent(mary,john).

• ancestor(X,Y) :- parent(X,Y). ancestor(X,Y) :- parent(X,Z),ancestor(Z,Y).

• ?- ancestor(bill,X)

Joseph’s Conjecture(1)

• CONJECTURE 1. Consistency And Logical Monotonicity (CALM).

• A program has an eventually consistent, coordination-free execution strategy if and only if it is expressible in (monotonic) Datalog.

Joseph’s Conjecture (2)

• CONJECTURE 2. Causality Required Only for Non-monotonicity (CRON).

• Program semantics require causal message ordering if and only if the messages participate in non-monotonic derivations.


• CONJECTURE 3. The minimum number of Dedalus timesteps required to evaluate a program on a given input data set is equivalent to the program’s Coordination Complexity.


• CONJECTURE 4. Any Dedalus program P can be rewritten into an equivalent temporally-minimized program P’ such that each inductive or asynchronous rule of P’ is necessary: converting that rule to a deductive rule would result in a program with no unique minimal model.

Circumstance has presented a rare opportunity—call it an imperative—for the database community to take its place in the sun, and help create a new environment for parallel and distributed computation to flourish.

------Joseph M. Hellerstein (UC Berkeley)

Open questions and conclusion

Open Questions

• What is the right consistency model?• What is the right programming model?• Whether and how to make use of caching?• How to balance functionality and scale?• What are the right cloud abstractions?• Cloud inter-operatability

VLDB 2010 Tutorial

Concluding

• Data Management for Cloud Computing poses a fundamental challenge to database researchers:– Scalability– Reliability– Data Consistency– Elasticity

• Database community needs to be involved – maintaining status quo will only marginalize our role.

VLDB 2010 Tutorial

New Textbook “Distributed System and Cloud computing”

《分布式系统与云计算》

96

分布式系统概述 (Introduction to Distributed System)

分布式云计算技术综述 ( Distributed Computing)

分布式云计算平台 (Cloud-based platform)分布式云计算程序开发 (Cloud-based

programming)

Further Reading

F. Chang et al. Bigtable: A distributed storage system for structured data. In OSDI, 2006. J. Dean and S. Ghemawat. MapReduce: Simplified data processing on large clusters. In OSDI, 2004. G. DeCandia et al. Dynamo: Amazon’s highly available key-value store. In SOSP, 2007.

S. Ghemawat, H. Gobioff, and S.-T. Leung. The Google File System. In Proc. SOSP, 2003.

D. Kossmann. The state of the art in distributed query processing. ACM Computing Surveys, 32(4):422–469, 2000.

Further Reading

Efficient Bulk Insertion into a Distributed Ordered Table (SIGMOD 2008)Adam Silberstein, Brian Cooper, Utkarsh Srivastava, Erik Vee, Ramana Yerneni, Raghu Ramakrishnan

PNUTS: Yahoo!'s Hosted Data Serving Platform (VLDB 2008)Brian Cooper, Raghu Ramakrishnan, Utkarsh Srivastava, Adam Silberstein, Phil Bohannon, Hans-Arno Jacobsen, Nick Puz, Daniel Weaver, Ramana Yerneni

Asynchronous View Maintenance for VLSD Databases,Parag Agrawal, Adam Silberstein, Brian F. Cooper, Utkarsh Srivastava and Raghu RamakrishnanSIGMOD 2009

Cloud Storage Design in a PNUTShellBrian F. Cooper, Raghu Ramakrishnan, and Utkarsh SrivastavaBeautiful Data, O’Reilly Media, 2009

Further Reading

F. Chang et al. Bigtable: A distributed storage system for structured data. In OSDI, 2006. J. Dean and S. Ghemawat. MapReduce: Simplified data processing on large clusters. In OSDI, 2004. G. DeCandia et al. Dynamo: Amazon’s highly available key-value store. In SOSP, 2007.

S. Ghemawat, H. Gobioff, and S.-T. Leung. The Google File System. In Proc. SOSP, 2003.

D. Kossmann. The state of the art in distributed query processing. ACM Computing Surveys, 32(4):422–469, 2000.

Thanks 谢谢！

apweb’2011 tutorial

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