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2 2 Google GFS Bigtable Mapreduce Yahoo Hadoop

3 3

4 4 - (CORBA)

5 Utility

6 6 Google Yahoo Aneka Greenplum Amazon dynamo

7 7 Hadoop HBase Google Apps MS Azure Amazon EC2

8 Cloud computing


10 Why we use cloud computing?

11 Case 1: Write a file Save Computer down, file is lost Files are always stored in cloud, never lost

12 Why we use cloud computing? Case 2: Use IE --- download, install, use Use QQ --- download, install, use Use C download, install, use …… Get the serve from the cloud

13 What is cloud and cloud computing? Cloud Demand resources or services over Internet scale and reliability of a data center.

14 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.

15 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.

16 IaaS Infrastructure as a Service PaaS Platform as a Service SaaS Software as a Service Types of cloud service

17 Software delivery model No hardware or software to manage Service delivered through a browser Customers use the service on demand Instant Scalability SaaS

18 Examples Your current CRM package is not managing the load or you simply dont want to host it in-house. Use a SaaS provider such as Your is hosted on an exchange server in your office and it is very slow. Outsource this using Hosted Exchange. SaaS

19 Platform delivery model Platforms are built upon Infrastructure, which is expensive Estimating demand is not a science! Platform management is not fun! PaaS

20 Examples You need to host a large file (5Mb) on your website and make it available for 35,000 users for only two months duration. Use Cloud Front from Amazon. You want to start storage services on your network for a large number of files and you do not have the storage capacity…use Amazon S3. PaaS

21 Computer infrastructure delivery model A platform virtualization environment Computing resources, such as storing and processing capacity. Virtualization taken a step further IaaS

22 Examples You want to run a batch job but you dont have the infrastructure necessary to run it in a timely manner. Use Amazon EC2. You want to host a website, but only for a few days. Use Flexiscale. IaaS

23 Cloud computing and other computing techniques

24 The 21 st Century Vision Of Computing Leonard Kleinrock, one of the chief scientists of the original Advanced Research Projects Agency Network (ARPANET) project which seeded the Internet, said: As of now, computer networks are still in their infancy, but as they grow up and become sophisticated, we will probably see the spread of computer utilities which, like present electric and telephone utilities, will service individual homes and offices across the country.

25 The 21 st Century Vision Of Computing Sun Microsystems co-founder Bill Joy He also indicated It would take time until these markets to mature to generate this kind of value. Predicting now which companies will capture the value is impossible. Many of them have not even been created yet.

26 The 21 st Century Vision Of Computing

27 Definitions Cloud Grid Cluster utility

28 Definitions Cloud Grid Cluster utility Utility computing is the packaging of computing resources, such as computation and storage, as a metered service similar to a traditional public utility

29 Definitions Cloud Grid Cluster utility A computer cluster is a group of linked computers, working together closely so that in many respects they form a single computer.

30 Definitions Cloud Grid Cluster utility Grid computing is the application of several computers to a single problem at the same time usually to a scientific or technical problem that requires a great number of computer processing cycles or access to large amounts of data

31 Definitions Cloud Grid Cluster utility Cloud computing is a style of computing in which dynamically scalable and often virtualized resources are provided as a service over the Internet.

32 Grid Computing & Cloud Computing share a lot commonality intention, architecture and technology Difference programming model, business model, compute model, applications, and Virtualization.

33 Grid Computing & Cloud Computing the problems are mostly the same manage large facilities; define methods by which consumers discover, request and use resources provided by the central facilities; implement the often highly parallel computations that execute on those resources.

34 Grid Computing & Cloud Computing Virtualization Grid do not rely on virtualization as much as Clouds do, each individual organization maintain full control of their resources Cloud an indispensable ingredient for almost every Cloud


36 Any question and any comments ?

37 37 Google GFS Bigtable Mapreduce Yahoo Hadoop

38 Google Cloud computing techniques

39 The Google File System

40 The Google File System (GFS) A scalable distributed file system for large distributed data intensive applications Multiple GFS clusters are currently deployed. The largest ones have: storage nodes 300+ TeraBytes of disk storage heavily accessed by hundreds of clients on distinct machines

41 Introduction Shares many same goals as previous distributed file systems performance, scalability, reliability, etc GFS design has been driven by four key observation of Google application workloads and technological environment

42 Intro: Observations 1 1. Component failures are the norm constant monitoring, error detection, fault tolerance and automatic recovery are integral to the system 2. Huge files (by traditional standards) Multi GB files are common I/O operations and blocks sizes must be revisited

43 Intro: Observations 2 3. Most files are mutated by appending new data This is the focus of performance optimization and atomicity guarantees 4. Co-designing the applications and APIs benefits overall system by increasing flexibility

44 The Design Cluster consists of a single master and multiple chunkservers and is accessed by multiple clients

45 The Master Maintains all file system metadata. names space, access control info, file to chunk mappings, chunk (including replicas) location, etc. Periodically communicates with chunkservers in HeartBeat messages to give instructions and check state

46 The Master Helps make sophisticated chunk placement and replication decision, using global knowledge For reading and writing, client contacts Master to get chunk locations, then deals directly with chunkservers Master is not a bottleneck for reads/writes

47 Chunkservers Files are broken into chunks. Each chunk has a immutable globally unique 64-bit chunk- handle. handle is assigned by the master at chunk creation Chunk size is 64 MB Each chunk is replicated on 3 (default) servers

48 Clients Linked to apps using the file system API. Communicates with master and chunkservers for reading and writing Master interactions only for metadata Chunkserver interactions for data Only caches metadata information Data is too large to cache.

49 Chunk Locations Master does not keep a persistent record of locations of chunks and replicas. Polls chunkservers at startup, and when new chunkservers join/leave for this. Stays up to date by controlling placement of new chunks and through HeartBeat messages (when monitoring chunkservers)

50 Operation Log Record of all critical metadata changes Stored on Master and replicated on other machines Defines order of concurrent operations Also used to recover the file system state

51 System Interactions: Leases and Mutation Order Leases maintain a mutation order across all chunk replicas Master grants a lease to a replica, called the primary The primary choses the serial mutation order, and all replicas follow this order Minimizes management overhead for the Master

52 Atomic Record Append Client specifies the data to write; GFS chooses and returns the offset it writes to and appends the data to each replica at least once Heavily used by Google s Distributed applications. No need for a distributed lock manager GFS choses the offset, not the client

53 Atomic Record Append: How? Follows similar control flow as mutations Primary tells secondary replicas to append at the same offset as the primary If a replica append fails at any replica, it is retried by the client. So replicas of the same chunk may contain different data, including duplicates, whole or in part, of the same record

54 Atomic Record Append: How? GFS does not guarantee that all replicas are bitwise identical. Only guarantees that data is written at least once in an atomic unit. Data must be written at the same offset for all chunk replicas for success to be reported.

55 Detecting Stale Replicas Master has a chunk version number to distinguish up to date and stale replicas Increase version when granting a lease If a replica is not available, its version is not increased master detects stale replicas when a chunkservers report chunks and versions Remove stale replicas during garbage collection

56 Garbage collection When a client deletes a file, master logs it like other changes and changes filename to a hidden file. Master removes files hidden for longer than 3 days when scanning file system name space metadata is also erased During HeartBeat messages, the chunkservers send the master a subset of its chunks, and the master tells it which files have no metadata. Chunkserver removes these files on its own

57 Fault Tolerance: High Availability Fast recovery Master and chunkservers can restart in seconds Chunk Replication Master Replication shadow masters provide read-only access when primary master is down mutations not done until recorded on all master replicas

58 Fault Tolerance: Data Integrity Chunkservers use checksums to detect corrupt data Since replicas are not bitwise identical, chunkservers maintain their own checksums For reads, chunkserver verifies checksum before sending chunk Update checksums during writes

59 Introduction to MapReduce

60 MapReduce: Insight Consider the problem of counting the number of occurrences of each word in a large collection of documents How would you do it in parallel ?

61 MapReduce 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]

62 Map 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. (docid, doc-content) Draw an analogy to SQL, map can be visualized as group-by clause of an aggregate query.

63 Reduce 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.

64 Pseudo-code map(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));

65 MapReduce: Execution overview

66 MapReduce: Example

67 MapReduce in Parallel: Example

68 MapReduce: Fault Tolerance Handled via re-execution of tasks. Task completion committed through master What happens if Mapper fails ? Re-execute completed + in-progress map tasks What happens if Reducer fails ? Re-execute in progress reduce tasks What happens if Master fails ? Potential trouble !!

69 MapReduce: Walk through of One more Application


71 MapReduce : PageRank PageRank models the behavior of a random surfer. C(t) is the out-degree of t, and (1-d) is a damping factor (random jump) The random surfer keeps clicking on successive links at random not taking content into consideration. Distributes its pages rank equally among all pages it links to. The dampening factor takes the surfer getting bored and typing arbitrary URL.

72 PageRank : Key Insights Effects at each iteration is local. i+1 th iteration depends only on i th iteration At iteration i, PageRank for individual nodes can be computed independently

73 PageRank using MapReduce Use Sparse matrix representation (M) Map each row of M to a list of PageRank credit to assign to out link neighbours. These prestige scores are reduced to a single PageRank value for a page by aggregating over them.

74 PageRank using MapReduce PageRank using MapReduce Map: distribute PageRank credit to link targets Reduce: gather up PageRank credit from multiple sources to compute new PageRank value Iterate until convergence Source of Image: Lin 2008

75 Phase 1: Process HTML Map task takes (URL, page-content) pairs and maps them to (URL, (PR init, list-of-urls)) PR init is the seed PageRank for URL list-of-urls contains all pages pointed to by URL Reduce task is just the identity function

76 Phase 2: PageRank Distribution Reduce task gets (URL, url_list) and many (URL, val) values Sum vals and fix up with d to get new PR Emit (URL, (new_rank, url_list)) Check for convergence using non parallel component

77 MapReduce: Some More Apps Distributed Grep. Count of URL Access Frequency. Clustering (K-means) Graph Algorithms. Indexing Systems MapReduce Programs In Google Source Tree

78 MapReduce: Extensions and similar apps PIG (Yahoo) Hadoop (Apache) DryadLinq (Microsoft)

79 Large Scale Systems Architecture using MapReduce User App MapReduce Distributed File Systems (GFS)

80 BigTable: A Distributed Storage System for Structured Data

81 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 Googles products

82 Motivation Lots of (semi-)structured data at Google URLs: Contents, crawl metadata, links, anchors, pagerank, … Per-user data: User preference settings, recent queries/search results, … Geographic locations: Physical entities (shops, restaurants, etc.), roads, satellite image data, user annotations, … Scale is large Billions of URLs, many versions/page (~20K/version) Hundreds of millions of users, thousands or q/sec 100TB+ of satellite image data

83 Why not just use commercial DB? Scale is too large for most commercial databases Even if it werent, 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

84 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

85 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

86 Building Blocks Building blocks: Google File System (GFS): Raw storage Scheduler: schedules jobs onto machines Lock service: distributed lock manager MapReduce: simplified large-scale data processing BigTable uses of building blocks: GFS: stores persistent data (SSTable file format for storage of data) Scheduler: schedules jobs involved in BigTable serving Lock service: master election, location bootstrapping Map Reduce: often used to read/write BigTable data

87 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

88 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.

89 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

90 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:,,, VS edu.gatech.math, edu.gatech.phys, edu.uga.math, edu.uga.phys

91 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

92 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

93 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

94 Implementation (cont.) Client data doesnt move through master server. Clients communicate directly with tablet servers for reads and writes. Most clients never communicate with the master server, leaving it lightly loaded in practice.

95 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

96 Tablet Location Since tablets move around from server to server, given a row, how do clients find the right machine? Need to find tablet whose row range covers the target row

97 Tablet Assignment Each tablet is assigned to one tablet server at a time. Master server keeps track of the set of live tablet servers and current assignments of tablets to servers. Also keeps track of unassigned tablets. When a tablet is unassigned, master assigns the tablet to an tablet server with sufficient room.

98 API Metadata operations Create/delete tables, column families, change metadata Writes (atomic) Set(): write cells in a row DeleteCells(): delete cells in a row DeleteRow(): delete all cells in a row Reads Scanner: read arbitrary cells in a bigtable Each row read is atomic Can restrict returned rows to a particular range Can ask for just data from 1 row, all rows, etc. Can ask for all columns, just certain column families, or specific columns

99 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)

100 Refinements: Bloom Filters Read operation has to read from disk when desired SSTable isnt 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

101 Refinements: Bloom Filters Read operation has to read from disk when desired SSTable isnt 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

102 102 Google GFS Bigtable Mapreduce Yahoo Hadoop

103 Yahoo Cloud computing

104 babycenter epicurious Search Results of the Future LinkedIn webmd Gawker New York Times

105 Whats in the Horizontal Cloud? Common Approaches to QA, Production Engineering, Performance Engineering, Datacenter Management, and Optimization Common Approaches to QA, Production Engineering, Performance Engineering, Datacenter Management, and Optimization ID & Account Management Monitoring & QoS Shared Infrastructure Metering, Billing, Accounting Horizontal Cloud Services Edge Content Services e.g., YCS, YCPI Provisioning & Virtualization e.g., EC2 Batch Storage & Processing e.g., Hadoop & Pig Operational Storage e.g., S3, MObStor, Sherpa Other Services Messaging, Workflow, virtual DBs & Webserving Security Simple Web Service APIs

106 Yahoo! Cloud Stack Provisioning (Self-serve) Horizontal Cloud Services …YCSYCPI Brooklyn EDGE Monitoring/Metering/Security Horizontal Cloud Services …Hadoop BATCH Horizontal Cloud Services …SherpaMOBStor STORAGE Horizontal Cloud Services VM/OS… APP Horizontal Cloud Services VM/OSyApache WEB Data Highway Serving Grid PHPApp Engine

107 Web Data Management Large data analysis (Hadoop) Structured record storage (PNUTS/Sherpa) Blob storage (SAN/NAS) Scan oriented workloads Focus on sequential disk I/O $ per cpu cycle CRUD Point lookups and short scans Index organized table and random I/Os $ per latency Object retrieval and streaming Scalable file storage $ per GB

108 The World Has Changed Web serving applications need: Scalability! Preferably elastic Flexible schemas Geographic distribution High availability Reliable storage Web serving applications can do without: Complicated queries Strong transactions

109 PNUTS / SHERPA To Help You Scale Your Mountains of Data

110 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 datacenters worldwide High Availability - outages cost $millions Variable usage patterns - as applications and users change 110

111 The PNUTS/Sherpa Solution The next generation global-scale record store Record-orientation: Routing, data storage optimized for low-latency record access Scale out: Add machines to scale throughput (while keeping latency low) Asynchrony: Pub-sub replication to far-flung datacenters to mask propagation delay Consistency model: Reduce complexity of asynchrony for the application programmer Cloud deployment model: Hosted, managed service to reduce app time-to-market and enable on demand scale and elasticity 111

112 E C A E B W C W D E F E What is PNUTS/Sherpa? E C A E B W C W D E F E CREATE TABLE Parts ( ID VARCHAR, StockNumber INT, Status VARCHAR … ) CREATE TABLE Parts ( ID VARCHAR, StockNumber INT, Status VARCHAR … ) Parallel database Geographic replication Structured, flexible schema Hosted, managed infrastructure A E B W C W D E E C F E 112

113 What Will It Become? E C A E B W C W D E F E E C A E B W C W D E F E E C A E B W C W D E F E CREATE TABLE Parts ( ID VARCHAR, StockNumber INT, Status VARCHAR … ) CREATE TABLE Parts ( ID VARCHAR, StockNumber INT, Status VARCHAR … ) Parallel database Geographic replication Indexes and views Structured, flexible schema Hosted, managed infrastructure

114 What Will It Become? E C A E B W C W D E F E E C A E B W C W D E F E E C A E B W C W D E F E Indexes and views

115 Scalability Thousands of machines Easy to add capacity Restrict query language to avoid costly queries Geographic replication Asynchronous replication around the globe Low-latency local access High availability and fault tolerance Automatically recover from failures Serve reads and writes despite failures Design Goals 115 Consistency Per-record guarantees Timeline model Option to relax if needed Multiple access paths Hash table, ordered table Primary, secondary access Hosted service Applications plug and play Share operational cost

116 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 YCA: Authorization PNUTS API Tabular API 116

117 Data Manipulation Per-record operations Get Set Delete Multi-record operations Multiget Scan Getrange 117

118 TabletsHash 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! Dont get scurvy! But at what price? How much did you pay for this lemon? Is this a vegetable? New Zealand The perfect fruit NameDescriptionPrice $12 $9 $1 $900 $2 $3 $1 $14 $2 $8 0x0000 0xFFFF 0x911F 0x2AF3 118

119 TabletsOrdered Table 119 Apple Banana Grape Orange Lime Strawberry Kiwi Avocado Tomato Lemon Grapes are good to eat Limes are green Apple is wisdom Strawberry shortcake Arrgh! Dont 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 NameDescriptionPrice A Z Q H

120 Flexible Schema Posted dateListing idItemPrice 6/1/ Couch$570 6/1/ Bike$86 6/3/ Car$1123 6/5/ Lamp$15 Color Red Condition Good Fair

121 Storage units Routers Tablet Controller REST API Clients Local region Remote regions Tribble Detailed Architecture 121

122 Tablet Splitting and Balancing 122 Each storage unit has many tablets (horizontal partitions of the table) Tablets may grow over time Overfull tablets split Storage unit may become a hotspot Shed load by moving tablets to other servers Storage unit Tablet


124 Accessing Data 124 SU 1 Get key k 2 3 Record for key k 4

125 Bulk Read 125 SU Scatter/ gather server SU 1 {k1, k2, … kn} 2 Get k 1 Get k 2 Get k 3

126 Storage unit 1Storage unit 2Storage unit 3 Range Queries in YDOT Clustered, ordered retrieval of records Storage unit 1 Canteloupe Storage unit 3 Lime Storage unit 2 Strawberry Storage unit 1 Router Apple Avocado Banana Blueberry Canteloupe Grape Kiwi Lemon Lime Mango Orange Strawberry Tomato Watermelon Apple Avocado Banana Blueberry Canteloupe Grape Kiwi Lemon Lime Mango Orange Strawberry Tomato Watermelon Grapefruit…Pear? Grapefruit…Lime? Lime…Pear? Storage unit 1 Canteloupe Storage unit 3 Lime Storage unit 2 Strawberry Storage unit 1

127 Updates 1 Write key k 2 7 Sequence # for key k 8 SU 3 Write key k 4 5 SUCCESS 6 Write key k Routers Message brokers 127


129 Asynchronous Replication 129

130 Goal: Make it easier for applications to reason about updates and cope with asynchrony What happens to a record with primary key Alice? Consistency Model 130 Time Record inserted Update Delete Time v. 1 v. 2 v. 3v. 4 v. 5 v. 7 Generation 1 v. 6 v. 8 Update As the record is updated, copies may get out of sync.

131 Example: Social Alice UserStatus AliceBusy West East UserStatus AliceFree UserStatus Alice??? UserStatus Alice??? UserStatus AliceBusy UserStatus Alice___ Busy Free Record Timeline

132 Time v. 1 v. 2 v. 3v. 4 v. 5 v. 7 Generation 1 v. 6 v. 8 Current version Stale version Read Consistency Model 132 In general, reads are served using a local copy

133 Time v. 1 v. 2 v. 3v. 4 v. 5 v. 7 Generation 1 v. 6 v. 8 Read up-to-date Current version Stale version Consistency Model 133 But application can request and get current version

134 Time v. 1 v. 2 v. 3v. 4 v. 5 v. 7 Generation 1 v. 6 v. 8 Read v.6 Current version Stale version Consistency Model 134 Or variations such as read forwardwhile copies may lag the master record, every copy goes through the same sequence of changes

135 Time v. 1 v. 2 v. 3v. 4 v. 5 v. 7 Generation 1 v. 6 v. 8 Write Current version Stale version Consistency Model 135 Achieved via per-record primary copy protocol (To maximize availability, record masterships automaticlly transferred if site fails) Can be selectively weakened to eventual consistency (local writes that are reconciled using version vectors)

136 Time v. 1 v. 2 v. 3v. 4 v. 5 v. 7 Generation 1 v. 6 v. 8 Write if = v.7 ERROR Current version Stale version Consistency Model 136 Test-and-set writes facilitate per-record transactions

137 Consistency Techniques Per-record mastering Each record is assigned a master region May differ between records Updates to the record forwarded to the master region Ensures consistent ordering of updates Tablet-level mastering Each tablet is assigned a master region Inserts and deletes of records forwarded to the master region Master region decides tablet splits These details are hidden from the application Except for the latency impact!

138 138 Mastering A E B W C W D E E C F E A E B W C W D E E C F E A E B W C W D E E C F E Tablet master

139 Bulk Insert/Update/Replace Client Source Data Bulk manager 1.Client feeds records to bulk manager 2.Bulk loader transfers records to SUs in batches Bypass routers and message brokers Efficient import into storage unit

140 Bulk Load in YDOT YDOT bulk inserts can cause performance hotspots Solution: preallocate tablets

141 Index Maintenance How to have lots of interesting indexes and views, without killing performance? Solution: Asynchrony! Indexes/views updated asynchronously when base table updated


143 Types of Record Stores Query expressiveness Simple Feature rich Object retrieval Retrieval from single table of objects/records SQL S3 PNUTS Oracle

144 Types of Record Stores Consistency model Best effort Strong guarantees Eventual consistency Timeline consistency ACID S3 PNUTS Oracle Program centric consistency Object-centric consistency

145 Types of Record Stores Data model Flexibility, Schema evolution Optimized for Fixed schemas CouchDB PNUTS Oracle Consistency spans objects Object-centric consistency

146 Types of Record Stores Elasticity (ability to add resources on demand) Inelastic Elastic Limited (via data distribution) VLSD (Very Large Scale Distribution /Replication) Oracle PNUTS S3

147 Data Stores Comparison User-partitioned SQL stores Microsoft Azure SDS Amazon SimpleDB Multi-tenant application databases Oracle on Demand Mutable object stores Amazon S3 Versus PNUTS More expressive queries Users must control partitioning Limited elasticity Highly optimized for complex workloads Limited flexibility to evolving applications Inherit limitations of underlying data management system Object storage versus record management

148 Application Design Space Records Files Get a few things Scan everything Sherpa MObStor Everest Hadoop YMDB MySQL Filer Oracle BigTable 148

149 Alternatives Matrix Elastic Operability Global low latency Availability Structured access Sherpa Y! UDB MySQL Oracle HDFS BigTable Dynamo Updates Cassandra Consistency model SQL/ACID 149

150 QUESTIONS? 150

151 Hadoop

152 Problem How do you scale up applications? Run jobs processing 100s of terabytes of data Takes 11 days to read on 1 computer Need lots of cheap computers Fixes speed problem (15 minutes on 1000 computers), but… Reliability problems In large clusters, computers fail every day Cluster size is not fixed Need common infrastructure Must be efficient and reliable

153 Solution Open Source Apache Project Hadoop Core includes: Distributed File System - distributes data Map/Reduce - distributes application Written in Java Runs on Linux, Mac OS/X, Windows, and Solaris Commodity hardware

154 Hardware Cluster of Hadoop Typically in 2 level architecture Nodes are commodity PCs 40 nodes/rack Uplink from rack is 8 gigabit Rack-internal is 1 gigabit

155 Distributed File System Single namespace for entire cluster Managed by a single namenode. Files are single-writer and append-only. Optimized for streaming reads of large files. Files are broken in to large blocks. Typically 128 MB Replicated to several datanodes, for reliability Access from Java, C, or command line.

156 Block Placement Default is 3 replicas, but settable Blocks are placed (writes are pipelined): On same node On different rack On the other rack Clients read from closest replica If the replication for a block drops below target, it is automatically re-replicated.

157 How is Yahoo using Hadoop? Started with building better applications Scale up web scale batch applications (search, ads, …) Factor out common code from existing systems, so new applications will be easier to write Manage the many clusters

158 Running Production WebMap Search needs a graph of the known web Invert edges, compute link text, whole graph heuristics Periodic batch job using Map/Reduce Uses a chain of ~100 map/reduce jobs Scale 1 trillion edges in graph Largest shuffle is 450 TB Final output is 300 TB compressed Runs on 10,000 cores Raw disk used 5 PB

159 Terabyte Sort Benchmark Started by Jim Gray at Microsoft in 1998 Sorting 10 billion 100 byte records Hadoop won the general category in 209 seconds 910 nodes 2 quad-core 2.0Ghz / node 4 SATA disks / node 8 GB ram / node 1 gb ethernet / node 40 nodes / rack 8 gb ethernet uplink / rack Previous records was 297 seconds

160 Hadoop clusters We have ~20,000 machines running Hadoop Our largest clusters are currently 2000 nodes Several petabytes of user data (compressed, unreplicated) We run hundreds of thousands of jobs every month

161 Research Cluster Usage

162 Who Uses Hadoop? Amazon/A9 AOL Facebook Fox interactive media Google / IBM New York Times PowerSet (now Microsoft) Quantcast Rackspace/Mailtrust Veoh Yahoo! More at

163 Q&A For more information: Website: Mailing lists:

164 164 Google GFS Bigtable Mapreduce Yahoo Hadoop





169 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 Ramakrishnan SIGMOD 2009 Cloud Storage Design in a PNUTShell Brian F. Cooper, Raghu Ramakrishnan, and Utkarsh Srivastava Beautiful Data, OReilly Media, 2009

170 Further Reading F. Chang et al. Bigtable: A distributed storage system for structured data. In OSDI, J. Dean and S. Ghemawat. MapReduce: Simplified data processing on large clusters. In OSDI, G. DeCandia et al. Dynamo: Amazons highly available key-value store. In SOSP, S. Ghemawat, H. Gobioff, and S.-T. Leung. The Google File System. In Proc. SOSP, D. Kossmann. The state of the art in distributed query processing. ACM Computing Surveys, 32(4):422–469, 2000.


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