The Art of Big Data

The road lies plain before me;--tis a theme Single and of determined bounds; … - Wordsworth, The Prelude m pre ss.co . word ol bl eclix te Scho p:/ /dou Gr adua 1 ka r, htt val Post 2 9,201 n a San r, Na Nov Krish in a st Sem hD Gue 00–PEC40

What is Big Data ? Big Data to smart data Bigo  Agenda Data o  To cover the broad Pipeline picture o  Understand the waypoints & o  Drill down into one area (NOSQL) Analytics/ Modeling Analytic Storage - R Algorithms NOSQL o  Can do others later … Processing -o  Of the Big Data Visualization Hadoop … domain …

Thanks to …The giants whose shoulders I am standing on Special Thanks to: Peter Ateshian, NPS Prof Murali Tummala, NPS Shirley Bailes,O’Reilly Ed Dumbill,O’Reilly Jeﬀ Barr,AWS Jenny Kohr Chynoweth,AWS

When I think of my own native land, In a moment I seem to be there; But, alas! recollection at hand Soon hurries me back to despair.- Cowper, The Solitude Of Alexander SelKirk

What is Big Data ?“Big data” is data “Big data” is less that becomes large about size, more enough that it about ﬂow & velocity cannot be processed - persisting using conventional petabytes per year is methods. @twitter easier than processing terabytes per hour. @twitter Ref: hIp://radar.oreilly.com/2010/09/the-‐smaq-‐stack-‐for-‐big-‐data.html

What is Big Data ? Vinod Khosla’s Cool Dozen!   Consumers : “Widespread innovation in technologies that reduce data overload for users” ~ Data Reduction   Businesses : “Simple solutions to handle the deluge of data generated from various sources …” ~ Big Data Analytics TV 2.0, EducaXon, Social NEXT,Tools for sharing inteerst,Publishing,… Ref: hIp://www.ciol.com/News/News/News-‐Reports/Vinod-‐Khosla%E2%80%99s-‐cool-‐dozen-‐tech-‐innovaXons/156307/0/ hIp://yourstory.in/2011/11/vinod-‐khoslas-‐keynote-‐at-‐nasscom-‐product-‐conclave-‐reject-‐punditry-‐believe-‐in-‐an-‐idea-‐take-‐risk-‐and-‐succeed/

EBC322   Volume o  Scale   Velocity o  Data change rate vs. decision window   Variety o  Diﬀerent sources & formats o  Structured vs. Unstructured   Variability o  Breadth of interpreta<on & o  Depth of analy<cs   Contextual o  Dynamic variability o  RecommendaXon   Connectedness hIp://doubleclix.wordpress.com/2011/09/13/when-‐is-‐big-‐data-‐really-‐big-‐data/ hIp://www.hpts.ws/posters/Poster2011_13_Bulkowski.pdf

I.  Two Main Types – based on collecXon i.  Big Data Streams o  Data in “moXon” o  TwiIer ﬁre hose, Facebook, G+ ii.  Big Data Logs o  Data “at rest” o  Logs, DW, external market data, POS, … II.  Typically, Big Data has a non-‐determinisXc angle as well … o  CreaXve Discovery o  IteraXve, Model based AnalyXcs o  Explore quesXons to ask III.  Smart Data = Big Data + context + embedded/interacXve (inference, reasoning) models o  Model Driven o  DeclaraXvely InteracXve hIp://www.slideshare.net/leonsp/hadoop-‐slides-‐11-‐what-‐is-‐big-‐data hIp://www.slideshare.net/Dataversity/wed-‐1550-‐bacvanskivladimircolor

AWS – 600 Billion objects!Twitter §  200 million tweets/day §  Peak 10,000/second §  How would you handle the ﬁre hose for social network analytics ? Zynga §  “Analytics company, not a gaming company!” §  Harvests data : 15 TB/day Storage §  Test new features §  4 U box = 40 TB, §  Target advertising 1 PB = 25 boxes ! §  §  230 million players/month hIp://goo.gl/dcBsQ

•  6 Billion Messages per day •  2 PB (w/compression) online •  6 PB w/ replicaXon •  250 TB/Month growth •  HBase Infrastructure

50 TB/Day Very systemaXc 240 nodes, 84 PB Diagram speaks volumes! Path Analysis Teradata InstallaXon A/B TesXng Ref: hIp://www.hpts.ws/sessions/2011HPTS-‐TomFastner.pdf

•  “… they didn’t need a genius, … but build the world’s most impressive dileIante … baIling the efficient human mind with spectacular flamboyant inefficiency” – Final Jeopardy by Stephen Baker •  15 TB memory, across 90 IBM 760 servers, in 10 racks •  1 TB of dataset •  200 Million pages processed by Hadoop •  This is a good example of Connected data –  Contextual w/ variability –  Breath of interpretaXon –  AnalyXcs depth hIp://doubleclix.wordpress.com/2011/03/01/the-‐educaXon-‐of-‐a-‐machine-‐%E2%80%93-‐review-‐of-‐book-‐%E2%80%9Cfinal-‐jeopardy%E2%80%9D-‐by-‐stephen-‐baker/ hIp://doubleclix.wordpress.com/2011/02/17/watson-‐at-‐jeopardy-‐a-‐race-‐of-‐machines/

Warehouse-‐style ApplicaXons Block Store Distributed Big Data ApplicaXons Storage Object Store NOSQL AnalyXcs Parallelism Map/Reduce Web HPC AnalyXcs Cloud Architecture Social Media Log Inference AnalyXcs Social RecommendaXon/ Graph Inference Engines Machine Knowledge Search, Learning Mahout Graph Indexing ClassiﬁcaXon, Clustering

“A towel is about the most massively useful thing an interstellar hitchhiker can have … any man who can hitch the length and breadth of the Galaxy, rough it … win through, and still know where his towel is, is clearly a man to be reckoned with.” - From The Hitchhikers Guide to the Galaxy, by Douglas Adams. Published by Harmony Books in 1979Big Data to Smart Data

Don’t throw away 1 any data ! Big data to smart data Be ready for diﬀerent 2 ways of organizing the data •  summary h;p://goo.gl/fGw7r

Big Data Pipeline If a problem has no solution, it is not a problem, but a fact, not to be solved but to be coped with, over time … - Peres’s Law

Big Data Pipeline •  Stages o  Collect o  Store o  Transform & Analyze o  Model & Reason o  Predict, Recommend & Visualize•  Different systems have different characteristics o  Infrastructure optimization based in application/hardware attributes correlation (short term) •  Hadoop, Splunk, internal Dashboard o  Application performance trends (medium term) •  Analytics, Modeling,… o  Product Metrics •  Feature set vs. usage, what is important to users, stratification •  Modeling using R, Visualization layers like Tableau

Big Data Pipeline Ref:h;p:goo.gl/Mm83k Infer-ability Model Internal dashboards Hand , Tableau Context coded Programs, Connectedness R, Mahout, … SQL, Variety BI Tools, Hadoop, Pig, Variability SQL Hive, .NET NOSQL, Logs, Dryad, Velocity Scribe, HDFS, XML, Various Flume, other <iles, … Volume Hadoop tools … Decomplexify! Contextualize! Network! Reason! Infer!

Build to Fail - “It is working” is not binary The NOSQL ! I AM monarch of all I survey; My right there is none to dispute; From the centre all round to the sea I am lord of the fowl and the brute - Cowper, The Solitude Of Alexander SelKirk

Agenda•  Opening Gambit –  NOSQL : Toil, Tears & Sweat ! •  The Pragmas –  ABCs of NOSQL [ACID, BASE & CAP] •  The Mechanics –  Algorithmics & Mechanisms (For reference) Referenced Links @ http://doubleclix.wordpress.com/2010/06/20/nosql-talk-references/

What is NOSQL Anyway ?•  NOSQL != NoSQL or NOSQL != (!SQL) •  NOSQL = Not Only SQL •  Can be traced back to Eric Evans[2]! –  You can ask him during the ayernoon session! •  Unfortunate Name, but is stuck now •  Non RelaXonal could have been beIer •  Usually OperaXonal, Deﬁnitely Distributed •  NOSQL has certain semanXcs – need not stay that way

NOSQL Key Value Column Document Graph In-‐memory SimpleDB CouchDB Neo4j Memcached Google MongoDB FlockDB BigTable Disk Based HBase Lotus Domino InﬁniteGraph Redis Cassandra Riak Tokyo Cabinet Dynamo HyperTable Voldemort Azure TS Ref: [22,51,52]

When I think of my own native land, In a moment I seem to be there; But, alas! recollection at hand Soon hurries me back to despair. - Cowper, The Solitude Of Alexander SelKirkNOSQL Tales from the fieldWHAT WORKS

•  Designer Augmenting RDBMS with a Distributed key Value Store[40 : A good talk by Geir]•  Invitation only designer brand sales•  Limited inventory sales – start at 12:00, members have 10 min to grab them. 500K mails every day•  Keeps brand value, hidden from search•  Interesting load properties•  Each item a row in DB-BUY NOW reserves it –  Cant order more•  Started out as a Rails app –  shared nothing•  Narrow peaks – half of revenue

Christian Louboutin Effect•  ½ amz for Louboutin•  Use Voldemort•  Inventory, Shopping Cart, Checkout•  Partition by prod ID•  Shared infrastructure – “fog” not “cloud’ - Joyent!•  In-memory inventory•  Not afraid of sale anymore! And SQL DBs are still relevant !

Typical NOSQL Example Bit.ly•  Bit,ly URL shortening service, uses MongoDB•  User, title, URL, hash, labels[I-5], sort by time•  Scale – ~50M users, ~10K concurrent, ~1.25B shortens per month•  Criteria: –  Simple, Zippy FAST, Very Flexible, Reasonable Durability, Low cost of ownership•  Sharded by userid

•  New kind of “dictionary” a word repository, GPS for English – context, pronunciations, twitter … developer API•  Characteristics[I-6,Tony Tam’s presentation] –  RO-centric, 10,000 reads for every write –  Hit a wall with MySQL (4B rows) –  MongoDB read was so good that memcached layer was not required –  MongoDB used 4 times MySQL storage•  Another example : –  Voldemort – Unified Communications, IP-Phone data stored keyed off of phone number. Data relatively stable

Large Hadron Collider@CERN•  DAS is part of giant data management enterprise (cms) –  Polygot Persistence (SQL + NOSQL, Mongo, Couch, memcache, HDFS, Luster, Oracle, mySQL, …)•  Data Aggregation System [I-1,I-2,I-3,I-4] –  Uses MongoDB –  Distributed Model, 2-6 pb data –  Combine info. from different metadata sources, query without knowing their existence, user has domain knowledge – but shouldn’t deal with various formats, interfaces and query semantics –  DAS aggregates, caches and presents data as JSON documents – preserving security & integrity And SQL DBs are still relevant !

Scaling Twitter• 

•  Digg –  RDBMS places burden on reads than writes[I-8] –  Looked at NOSQL, selected Cassandra •  Colum oriented, so more structure than key-value•  Heard from noSQL Boston[http://twitter.com/ #search?q=%23nosqllive] –  Baidu: 120 node HyperTable cluster managing 600TB of data –  StumbleUpon uses HBase for Analytics –  Twitter’s Current Cassandra cluster: 45 nodes

•  Adob is a HBase shop •  BBC is a CouchDB shop [I-10,I-11,2] [I-13]•  Adobe SaaS Infrastructure – •  Sweet spot: tagging, content aggregation, •  Multi-master, multi search, storage and so forth datacenter replication•  Dynamic schema & huge number of records[I-5]•  40 million records in 2008 to 1 billion with 50 ms response •  Interactive Mediums•  NOSQL not mature in 2008, •  Old data to CouchDB now good enough •  Thus free up DB to do•  Prod Analytics:40 nodes, work! largest has 100 nodes

•  Cloudkick is a Cassandra shop[I-12]•  Cloudkick offers cloud management services•  Store metrics data•  Linear scalability for write load•  Massive write performance •  Memory table & serial commit log•  Low operational costs•  Data Structure –  Metrics, Rolled-up data, Statuses at time slice : all indexed by timestamp

•  Guardian/UK –  Runs on Redis[I-14] ! –  “Long-term The Guardian is looking towards the adoption of a schema-free database to sit alongside its Oracle database and is investigating CouchDB. … the relational database is now just a component in the overall data management story, alongside data caching, data stores, search engines And SQL DBs are etc. still relevant ! –  NOSQL can increase performance of "The evil that SQL relational data by offloading specific DBs do lives after data and tasks them; the good is oft interred with their bones...",

NOSQL at Netflix•  Netflix is fully in the cloud•  Uses NOSQL across the globe•  Customer Profiles, watchlog, usage logging (see next slide) –  No multi-record locking•  No DBA !•  Easier Schema Changes•  Less complex, Highly Available data store•  Joins happen in the applications http://www.hpts.ws/sessions/nosql-ecosystem.pdf http://www.hpts.ws/sessions/GlobalNetflixHPTS.pdf

21 NOSQL Themes•  Web Scale •  Scale Incrementally/conXnuous growth •  Oddly shaped & exponenXally connected •  Structure data as it will be used – i.e. read, query •  Know your queries/updates in advance[96], but you can change them later •  Compute aIributes at run Xme •  Create a few large enXXes with opXonal parts –  NormalizaXon creates many small enXXes •  Deﬁne Schemas in models (not in databases) •  Avoid impedance mismatch •  Narrow down & solve your core problem •  Solve the right problem with the right tool Ref: [I-‐8]

21 NOSQL Themes•  ExisXng soluXons are clunky[1] (in certain situaXons) •  Scale automaXcally, “becoming prohibiXvely costly (in terms of manpower) to operate” TwiIer[I-‐9] •  DistribuXon & parXXoning are built-‐in NOSQL •  RDBMS distribuXon & sharding not fun and is expensive –  Lose most funcXonality along the way •  Data at the center, Flexible schema, Less joins •  The value of NOSQL is in ﬂexibility as much as it is in “Big Data”

21 NOSQL Themes•  Requirements[3] –  Data will not ﬁt in one node •  And so need data parXXon/distribuXon by the system –  Nodes will fail, but data needs to be safe – replicaXon! –  Low latency for real-‐Xme use •  Data Locality –  Row based structures will need to read whole row, even for a column –  Column based structures need to scan for each row •  SoluXon : Column storage with Locality –  Keep data that is read together, don’t read what you don’t care •  For example friends – other data Ref: 3

ABCs of NOSQL - ACID, BASE & CAPThe woods are lovely, dark, and deep, But I have promises to keep, And miles to go before I sleep, And miles to go before I sleep. -Frost

CAP Principle“CAP Principle → Strong Consistency, High Availability, Consistency Par::on-‐resilience: Pick at most 2”[37] Availability Partition Which feature to discard depends on the nature of your system[41]

CAP Principle“CAP Principle → Strong Consistency, High Availability, Consistency Par::on-‐resilience: Pick at most 2”[37] C-‐A No P → Single DB server, no network par::on Availability Partition Which feature to discard depends on the nature of your system[41]

CAP Principle“CAP Principle → Strong Consistency, High Availability, Consistency Par::on-‐resilience: Pick at most 2”[37] C-‐P No A → Block transac:on in case of par::on failure Availability Partition Which feature to discard depends on the nature of your system[41]

CAP Principle Interesting (& controversial) from“CAP Principle → NOSQL perspective Strong Consistency, High Availability, Consistency Par::on-‐resilience: Pick at most 2”[37] A-‐P No C → Expira:on based caching, vo:ng majority Availability Partition

ABCs of NOSQL •  ACID o  Atomicity, Consistency, IsolaXon & Durability – fundamental properXes of SQL DBMS •  BASE[35,39] o  Basically Available Soy state(Scalable) Eventually Consistent •  CAP[36,39] o  Consistency, Availability & ParXXoning o  This C is ~A+C •  i.e. Atomic Consistency[36]

ACID •  Atomicity o  All or nothing •  Consistent o  From one consistent state to another •  e.g. ReferenXal Integrity o  But it is also applicaXon dependent on •  e.g. min account balance •  Predicates, invariants,… •  IsolaXon •  Durability

CAP Pragmas •  PrecondiXons o  The domain is scalable web apps o  Low Latency For real Xme use o  A small sub-‐set of SQL FuncXonality o  Horizontal Scaling •  PritcheI[35] talks about relaxing consistency across funcXonal groups than within funcXonal groups •  Idempotency to consider o  Updates inc/dec are rarely idempotent o  Order preserving trx are not idempotent either o  MVCC is an answer for this (CouchDB)

Consistency •  Strict Consistency o Any read on Data X will return the most recent write on X[42] •  SequenXal Consistency o Maintains sequenXal order from mulXple processes (No menXon of Xme) •  Linearizability o Add Xmestamp from loosely synchronized processes

Consistency •  Write availability, not read availability[44] •  Even load distribuXon is easier in eventually consistent systems •  MulX-‐data center support is easier in eventually consistent systems •  Some problems are not solvable with eventually consistent systems •  Code is someXmes simpler to write in strongly consistent systems

CAP EssenXals – 1 of 3 •  “CAP Principle → Strong Consistency, High Availability, ParXXon-‐resilience: Pick at most 2”[37] o  C-‐A No P → Single DB server, no network parXXon o  C-‐P No A → Block transacXon in case of parXXon failure o  A-‐P No C → ExpiraXon based caching, voXng majority •  Which feature to discard depends on the nature of your system[41]

CAP EssenXals – 2 of 3 •  Yield vs. Harvest[37] o  Yield → Probability of compleXng a request o  Harvest → FracXon of data reﬂected in the response •  Some systems tolerate < 100% harvest (e.g search i.e. approximate answers OK) others need 100% harvest (e.g. Trx i.e. correct behavior = single well deﬁned response) •  For sub-‐systems that tolerate harvest degradaXon, CAP makes sense

CAP EssenXals – 3 of 3 •  Trading Harvest for yield – AP •  ApplicaXon decomposiXon & use NOSQL in appropriate sub-‐systems that has state management and data semanXcs that match the opera<onal feature & impedance o  Hence NotOnly SQL not No SQL o  Intelligent homing to tolerate parXXon failures[44] o  MulX zones in a region (150 miles -‐ 5 ms) o  TwiIer tweets in Cassandra & MySQL o  BBC using MongoDB for oﬄoading DBMS o  Polygot persistence at LHC@CERN

CAP EssenXals – 3 of 3 •  Trading Harvest for yield – AP •  ApplicaXon decomposiXon & use NOSQL in appropriate sub-‐systems that has state management and data semanXcs that match the opera<onal feature & impedance o  Hence NotOnly SQL not No SQL o  Intelligent homing to tolerate parXXon failures[44] o  MulX zones in a region (150 miles -‐ 5 ms) o  TwiIer tweets in Cassandra and MySQL Most important o  BBC using MongoDB for oﬄoading DBMS point in the whole o  Polygot persistence at LHC@CERN presentation

Eventual Consistency & AMZ •  DistribuXon Transparency[38] •  Larger distributed systems, network parXXons are given •  Consistency Models o  Strong o  Weak •  Has an inconsistency window before update and guaranteed view o  Eventual •  If no new updates, all will see the value, eventually

Eventual Consistency & AMZ •  Guarantee variaXons[38] o Read-‐Your-‐writes o Session consistency o Monotonic Read consistency •  Access will not return previous value o Monotonic Write consistency •  Serialize write by the same process •  Guarantee order (vector clocks, mvcc) o  Example : Amz Cart merger (let cart add even with parXal failure)

Eventual Consistency & AMZ -‐ SimpleDB •  SimpleDB strong consistency semanXcs [49,50] o UnXl Feb 2010, SimpleDB only supported eventual consistency i.e. GetAIributes ayer PutAIributes might not be the same for some Xme (1 second) o On Feb 24, AWS Added ConsistentRead=True aIribute for read o Read will reﬂect all writes that got 200OK Xll that Xme!

Eventual Consistency & AMZ -‐ SimpleDB •  SimpleDB strong consistency semanXcs [49,50] o Also added condiXonal put/delete o Put aIribute has a speciﬁed value (Expected.1.Value=) or (Expected. 1.Exists = true/false) o Same condiXonal check capability for delete also o  Only on one aIribute !

Eventual Consistency & AMZ – S3 •  S3 is an eventual consistency system o Versioning o “S3 PUT & COPY synchronously store data across mulXple faciliXes before returning SUCCESS” o Repair Lost redundancy, repair bit-‐rot o Reduced Redundancy opXon for data that can be reproduced (99.999999999% vs. 99.99%) •  Approx 1/3rd less o CloudFront for caching

!SQL ? •  “We conclude that the current RDBMS code lines, while aIempXng to be a “one size ﬁts all” soluXon, in fact, excel at nothing. Hence, they are 25 year old legacy code lines that should be reXred in favor of a collecXon of “from scratch” specialized engines.”[43] •  “Current systems were built in an era where resources were incredibly expensive, and every compuXng system was watched over by a collecXon of wizards in white lab coats, responsible for the care, feeding, tuning and opXmizaXon of the system. In that era, computers were expensive and people were cheap” •  “The 1970 -‐ 1985 period was a <me of intense debate, a myriad of ideas, & considerable upheaval. We predict the next ﬁUeen years will have the same feel “

Further deliberaXon •  Daniel Abadi[45],Mike Stonebreaker[46], James Hamilton[47], Pat Hilland[48] are all good read for further deliberaXons

NOSQL Internals & Algorithmics

Caveats •  A representaXve subset of the mechanics and mechanisms used in the NOSQL world •  Being reﬁned & newer ones are being tried •  At a system level – to show how the techniques play a part to deliver a capability •  The NOSQL Papers and other references for further deliberaXon •  Even if we don’t cover fully, it is OK. I want to introduce some of the concepts so that you get an appreciaXon …

NOSQL Mechanics •  Horizontal Scalability •  Performance –  Gossip (Cluster –  SStables/memtables membership) –  LSM w/Bloom Filter –  Failure DetecXon •  Integrity/Version –  Consistent Hashing reconcilia<on –  ReplicaXon –  Timestamps Techniques –  Vector Clocks •  Hinted Handoﬀ •  Merkle Trees –  MVCC –  Sharding MongoDB –  SemanXc vs. syntacXc reconciliaXon –  Regions in HBase

Consistent Hashing •  Origin: web caching “To decrease ‘hot spots’ •  Three goals[87] –  Smooth evoluXon •  When a new machine joins, minimum rebalance work and impact –  Spread •  Objects assigned to a min number of nodes –  Load •  # of disXnct objects assigned to a node is small

Consistent Hashing •  Hash Keyspace/Token is divided into parXXons/ranges •  Cassandra – choice –  OrderPreserving parXXoner – key = token (for range queries) –  Also saw a CollaXngOrderPreservingParXXoner •  ParXXons assigned to nodes that are logically arranged in a circle topology •  Amz (dynamo) – assign sets of (random) mulXple points to diﬀerent machines depending on load •  Cassandra – monitor load & distribute •  Speciﬁc join & leave protocols •  ReplicaXon – next 3 consecuXve •  Cassandra – Rack-‐aware, Datacenter-‐aware

Consistent Hashing -‐ Hinted-‐handoﬀ •  What happens when a node is not available ? –  May be under load –  May be network parXXon •  Sloppy Quorum & Hinted-‐handoﬀ •  R/W performed on the 1st n healthy nodes •  Replica sent to a host node with hint in metadata & then transferred when the actual node is up •  Burdens neighboring nodes •  Cassandra 0.6.2 default is disabled (I think)

Consistent Hashing -‐ ReplicaXon •  What happens when a new node joins ? – It gets one or more parXXons – Dynamo : Copy the whole parXXon – Cassandra : Replicate keyset – Cassandra : working on a bit torrent type protocol to copy from replicas

AnX-‐entropy •  Merge and reconciliaXon operaXons –  Operate on two states and return a new state[86] •  Merkle Trees –  Dynamo use of Merkle trees to detect inconsistencies between replicas –  AnXEntropy in Cassandra exchanges Merkle trees and if they disagree, range repair via compacXon [91,92] –  Cassandra uses the ScuIlebuI ReconciliaXon[86]

Gossip •  Membership & Failure detecXon •  Based on emergence without rigidity – pulse coupled oscillators, biological systems like ﬁreﬂies ![90] •  Also used for state propagaXon –  Used in Dynamo/Cassandra

Gossip •  Cassandra exchanges heartbeat state, applicaXon state and so forth •  Every second, random live node, random unreachable node and exchanges key-‐value structures •  Some nodes play the part of seeds •  Seed /iniXal contact points in staXc conf file storage.conf file •  Could also come from a configuraXon service like zookeeper •  To guard against node flap, explicit membership join and leave – now you know why hinted handoff was added

Membership & Failure detecXon •  Consensus & Atomic Broadcast -‐ impossible to solve in a distributed system[88,89] –  Cannot diﬀerenXate between an slow system and a crashed system •  Completeness –  Every system that crashed will be eventually detected •  Correctness –  A correct process is never suspected •  In short, if you are dead somebody will no<ce it and if you are alive, nobody will mistake you for dead !

Ø Accrual Failure Detector •  Not Boolean value but a probabilisXc number that “accrues” over an exponenXal scale •  Captures the degree of conﬁdence that a corresponding monitored process has crashed[94] –  Suspicion Level –  Ø = 1 -‐> prob(error) 10% –  Ø = 2 -‐> prob(error) 1% –  Ø = 3 -‐> prob(error) 0.1% •  If process is dead, –  Ø is monotonically increasing & Ø→α as t →α •  If process is alive and kicking, Ø=0 •  Account for lost messages, network latency and actual crash of system/process •  Well known heartbeat period Δi, then network latency Δtr can be tracked by inter-‐arrival Xme modeling

Write/Read Mechanisms •  Read & Write to a random node (StorageProxy) •  Proxy coordinates the read and write strategy (R/W = any, quorum et al) •  Memtables/SSTables from big table •  Bloom Filter/Index •  LSM Trees

Hbase – WAL, Node Write Memstore, HDFS File system Commit Logs Node M e m o MemTable r y Read Flushing Index Index Index D i BF BF BF s kSSTable• Immutable• Compaction• Maintain Index & Bloom Filter

How… does HBase work again? http://www.larsgeorge.com/2010/01/hbase-architecture-101-write-ahead-log.html http://hbaseblog.com/2010/07/04/hug11-hbase-0-90-preview-wrap-up/

Bloom Filter •  The BloomFilter answers the quesXon •  “Might there be data for this key in this SSTable?” [Ref: Cassandra/Hbase mailer] –  “Maybe" or –  “Deﬁnitely not“ –  When the BloomFilter says "maybe" we have to go to disk to check out the content of the SSTable •  Depends on implementaXon –  Redone in Cassandra –  Hbase 0.20.x removed, will be back in 0.90 with a “jazzy” implementaXon

Was it a vision, or a waking dream?Fled is that music:—do I wake or sleep? -Keats, Ode to a Nightingale

•  http://www.readwriteweb.com/enterprise/2011/11/infographic-data- deluge---8-ze.php•  http://www.crn.com/news/data-center/232200061/efficiency-or- bust-data-centers-drive-for-low-power-solutions-prompts-channel- growth.htm•  http://www.quantumforest.com/2011/11/do-we-need-to-deal-with- big-data-in-r/•  http://www.forbes.com/special-report/2011/migration.html•  http://www.mercurynews.com/bay-area-news/ci_19368103•  http://www.businessinsider.com/apple-new-data-center-north- carolina-created-50-jobs-2011-11

The Art of Big Data

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