1. Database as a ServiceSeminar, ICDE 2010, Long Beach, March 04 Wolfgang Lehner | Dresden University of Technology, Germany Kai-Uwe Sattler | Ilmenau University of Technology, Germany 1

2. Introduction Motivation SaaS Cloud Computing UseCases 2

3. Software as a Service (SaaS) Traditional Software On-DemandUtility Plug In, SubscribePay-per-Use Build Your Own 3

4. Comparison of business model 4

5. Avoidhiddencostof traditional SW Traditional Software SaaS SW Licenses Subscription Fee Training Training Customization Hardware IT Staff Maintenance Customization 5

6. The Long Tail Dozens of markets of millions or millions of markets of dozens? Your Large Customers $ / Customer What if you lower your cost of sale (i.e. lower barrier to entry) and you also lower cost of operations Your Typical Customers New addressable market >> current market (Currently) “non addressable” Customers # of Customers 6

7. Acquisition Model Service Business Model Pay for usage Access ModelInternet Technical ModelScalable, elastic, shareable EC2 & S3 "All that matters is results — I don't care how it is done" Cloud Computing: A style of computing where massively scalable, IT-enabled capabilities are provided "as a service" across the Internet to multiple external customers. "I don't want to own assets — I want to pay for elastic usage, like a utility" "I want accessibility from anywhere from any device" "It's about economies of scale, with effective and dynamic sharing" What is Cloud? – Gartner’s Definition 7

8. To Qualify as a Cloud Common, Location-independent, Online Utility on Demand* Common implies multi-tenancy, not single or isolated tenancy Utility implies pay-for-use pricing onDemandimplies ~infinite, ~immediate, ~invisible scalability Alternatively, a “Zero-One-Infinity” definition:** 0On-premise infrastructure, acquisition cost, adoption cost, support cost 1Coherent and resilient environment – not a brittle “software stack” Scalability in response to changing need, Integratability/ Interoperability with legacy assets and other services Customizability/Programmability from data, through logic, up into the user interface without compromising robust multi-tenancy * Joe Weinman, Vice President of Solutions Sales, AT&T, 3 Nov. 2008 ** From The Jargon File: “Allow none of foo, one of foo, or any number of foo” 8

9. Cloud Differentials: Service Models 9 Cloud Software as a Service (SaaS) Use provider’s applications over a network Cloud Platform as a Service (PaaS) Deploy customer-created applications to a cloud Cloud Infrastructure as a Service (IaaS) Rent processing, storage, network capacity, and other fundamental computing resources

10. Cloud Differentials: Characteristics 10 Platform Physical – Virtual Homogenous – Heterogeneous Design Paradigms Storage CPU Bandwidth Usage Model Exclusive Shared Pseudo-Shared Size/Location Large Scale(AWS, Google, BM/Google), Small Scale(SMB, Academia) Purpose General Purpose Special Purpose (e.g., DB-Cloud) Administration/Jurisdiction Public Private

11. UseCases: Large-Scale Data Analytics Outsourceyourdata and usecloudresourcesforanalysis Historical and mostlynon-criticaldata Parallelizable, read-mostlyworkload, high variantworkloads Relaxed ACID guarantees Examples (HadoopPoweredBy): Yahoo!: researchfor ad systems and Web search Facebook: reporting and analytics Netseer.com: crawling and log analysis Journey Dynamics: trafficspeedforecasting 11

12. UseCases: Database Hosting Public datasets Biologicaldatabases: a singlerepositoryinstead of > 700 separate databases Semantic Web Data, Linkeddata, ... Sloan Digital Sky Survey TwitterCache Already on Amazon AWS: annotated human genomedata, US census, Freebase, ... Archiving, Metadata Indexing, ... 12

13. UseCases: Service Hosting Data managementforSaaSsolutions Run theservicesnearthedata = ASP Alreadymanyexistingapplications CRM, e.g. Salesforce, SugarCRM Web Analytics Supply Chain Management HelpDesk Management Enterprise ResourcePlanning, e.g. SAP Business ByDesign ... 13

14. Foundations & Architectures Virtualization Programmingmodels Consistencymodels & replication SLAs & Workloadmanagement Security 14

15. Topics covered in this Seminar Query & Programming Model Logical Data Model Virtuali-zation Multi-Tenancy Service Level Agreements Storage Model DistributedStorage Replication Security 15

16. Current Solutions userperspective one DB for all clients one DB per client Virtualization Replication 16 DistributedStorage physicalperspective

17. ... it‘s simple! 17

18. Virtualization Separating the abstract view of computing resources from the implementation of these resources addsflexibility and agility to the computing infrastructure soften problems related to provisioning, manageability, … lowers TCO: fewercomputingresources Classicaldrivingfactor: serverconsolidation 18 E-mail server Web server Database server E-mail server Database server Linux Linux Linux Linux Linux EDBT2008 Tutorial (Aboulnaga e.a.) Web server Linux Virtualization Consolidate  Improved utilization using consolidation

19. Whatcanbevirtualized – thebigfour. 19

20. Different TypesofVirtualization 20 APP 1 APP 4 APP 2 APP 3 APP 5 OPERATING SYSTEM OPERATING SYSTEM VIRTUAL MACHINE 1 VIRTUAL MACHINE 2 CPU CPU CPU MEM MEM NET VIRTUAL MACHINE MONITOR (VMM) PHYSICAL STORAGE PHYSICAL MACHINE CPU MEM NET CPU CPU

21. Virtual Machines 21 Technique with long history (since the 1960's) Prominent since IBM 370 mainframeseries Today large scale commodity hardware and operating systems Virtual Machine Monitor (Hypervisor) strong isolation between virtual machines (security, privacy, fault tolerance) flexible mapping between virtual machines and physical resources classical operationspause, resume, checkpoint, migrate (admin / load balancing) Software deployment Preconfigured virtual appliances Repositories of virtual appliances on the web

22. DBMS on top of Virtual Machines ... yetanotherapplication? ... Overhead? SQL Server withinVMware 22

23. Virtualization Design Advisor What fraction of node resources goes to what DBMS? Configuring VM parameters What parameter settings are best for a given resource configuration Configuringthe DBMS parameters Example Workload 1: TPC-H (10GByte) Workload 2: TPC-H (10GByte) only Q18 (132 copies) Virtualization design advisor 20% of CPU to Workload 1 80% of CPU to Workload 2 23

24. Some Experiments Workload Definition based on TPC-H Q18 isoneofthemost CPU intensive queries Q21 isoneofthe least CPU intensive queries Workload Units C: 25x Q18 I: 1x Q21 Experiment: Sensitivity to workloadResource Needs W1 = 5C + 5I W2 = kC + (10-k)I (increaseof k -> more CPU intensive) Postgres DB2 24

25. Some Experiments (2) Workload Settings W3 = 1C W4 = kC Workload Settings W5 = 1C W6 = kI 25

26. Virtualization in DBaaS environments DB Layer DB Server DB Server DB Server DB DB DB DB DB Instance Layer Instance Instance Instance Instance Instance Instance DB Server Layer VM VM VM VM VM VM VM Layer HW Layer 26

28. MQTs

29. MDC

31. VM expects static (peak) resource requirements

33. Resources Configuration

34. (manual) MigrationHW Layer 27

35. Layer Interactions (2) Experiment DB2 on Linux TPC-H workload on 1GB database Ranges for resource grants Main memory (BP) – 50 MB to 1GB Additional storage (Indexes) – 5% to 30% DB size Varying advisor output (17-26 indexes) Different possible improvement Different expected Performance after improvement DB Advisor Expected Performance Possible Improvement Index Storage Index Storage 35% 90% 25% 25% 20% 20% 15% 15% <1% <3% 10% 10% VM Configuration 5% 5% 200 MB 400 MB 600 MB 800 MB 1 GB 200 MB 400 MB 600 MB 800 MB 1 GB BP BP 28

36. Storage Virtualization General Goal provide a layerofindircetiontoallowthedefinitionofvirtualstoragedevices minimize/avoiddowntime (local and remote mirroring) improveperformance (distribution/balancing – provisioning - controlplacement) reducecostofstorageadministration Operations create, destroy, grow, shrinkvirtualdevices changesize, performance, reliability, ... workloadfluctuations hierarchicalstoragemanagement versioning, snapshots, point-in-time copies backup, checkpoints exploit CPU and memory in the storage system caching executelow-level DBMS functions 29

37. Virtualization in DBaaS Environments (2) DB Layer DB Server DB Server DB Server DB DB DB DB DB Instance Layer Instance Instance Instance Instance Instance Instance DB Server Layer VM VM VM VM VM VM VM Layer Shared Disk HW Layer Storage Layer 30 Local Disk

39. MQTs

40. MDC

42. Replication

43. ArchivingShared Disk Local Disk

44. Onewaytogo? Paravirtualization CPU and Memory Paravirtualization extendstheguest to allow direct interaction withtheunderlyinghypervisor reducesthemonitorcostincludingmemoryand System calloperations. gainsfromparavirtualizationareworkloadspecific Device Paravirtualization places a highperformancevirtualization-aware device driver into the guest paravirtualizeddriversaremoreCPU efficient (less CPU overhead forvirtualization) Paravirtualizeddriverscanalso take advantage of HW features, like partial offload

45. Outline Query & Programming Model Logical Data Model Virtuali-zation Multi-Tenancy Service Level Agreements Storage Model DistributedStorage Replication Security 33

47. Extensibility: customer-specificschemachanges

48. Security: preventingunauthorizeddataaccessesbyothertenants

49. Performance/scalability: scale-up & scale-out

50. Maintenance: on tenantlevelinstead of on databaselevel34

51. Flexible Schema Approaches Goal: allowtenant-specificschemaadditions (columns) Universal Table Extension Table PivotTable 35

52. Flexible Schema Approaches: Comparison Best performance Flexible schemaevolution Pivottable Extension table Chunkfolding Private tables Applicationownstheschema Database ownstheschema Universal table XML columns Universal table: requirestechniquesforhandlingsparsedata Fine-grainedindexsupportnotpossible Pivottable: Requiresjoinsforreconstructinglogicaltuples Chunkfolding: similar to pivottables Group of columnsarecombined in a chunk and mappedinto a chunktable Requirescomplexquerytransformation 36

53. Access Control in Multi-Tenant DB Shared DB approachesrequirerow-levelaccesscontrol Query transformation.... whereTenantID = 42 ... Potential securityrisks DBMS-levelcontrol, e.g. IBM DB2 LBAC Label-based Access control Controls read/writeaccess to individualrows and columns Securitylabelswithpolicies Requires separate accountforeachtenant 37

54. In a Nutshell How shall virtualization be handled on Machine level (VM to HW) DBMS level (database to instance to database server) Schema level (multi tenancy) ... using … Allocation between layers Configuration inside layers Flexible schemas … when … Characteristics of the workloads are known Virtual machines are transparent Tenant-specific schema extensions … demanding that … SLAs and security are respected Each node’s utilization is maximized Number of nodes is minimized 38

55. Outline Query & Programming Model Logical Data Model Virtuali-zation Multi-Tenancy Service Level Agreements Storage Model DistributedStorage Replication Security 39

56. MapReduce Background 40 Programming model and an associated implementation for large-scale data processing Google and related approaches: Apache Hadoop and Microsoft Dryad User-defined map & reduce functions Infrastructure hides details of parallelization provides fault-tolerance, data distribution, I/O scheduling, load balancing, ... map (in_key, in_value) -> (out_key, intermediate_value) list reduce (out_key,intermediate_value list) -> out_value list M { (key,value) } R M R M

57. Logic Flow of WordCount Mapper Hadoop Map/Reduce is a software framework for easily writing applications which process vast amounts of data (multi-terabyte data-sets) in-parallel on large clusters (thousands of nodes) of commodity hardware in a reliable, fault-tolerant manner… 1  Hadoop Map/Reduce is a Hadoop 1 Map  1 17  software framework for Reduce  1 is  1 45  easily writing applications a  1 … … Sort/Shuffle Reducer Hadoop [1, 1, 1, …,1] Hadoop 5 Map  [1, 1, 1, …, 1] Map  12 Reduce  [1, 1, 1, …, 1] Reduce  12 is  [1, 1, 1, …, 1] is  42 a  [1, 1, 1, …, 1] a  23

58. MapRecude Disadvantages Extremely rigid data flow Common operations must be coded by hand join, filter, split, projection, aggregates, sorting, distinct User plans may be suboptimal and lead to performance degradation Semantics hidden inside map-reduce functions Inflexible, difficult to maintain, extend and optimize Combination of high-level declarative querying and low-level programming with MapReduce  Dataflow Programming Languages Hive, JAQL and Pig M R 42

59. PigLatin PigLatin On top of map-reduce/ Hadoop Mix of declarative style of SQL and procedural style of map-reduce Consists of two parts PigLatin: A Data Processing Language Pig Infrastructure: An Evaluator for PigLatin programs Pig compiles Pig Latin into physical plans Plans are to be executed over Hadoop 30% of all queriesat Yahoo! in Pig-Latin Open-source, http://incubator.apache.org/pig 43

61. Implementation in MapReduce 45

63. group, filter, foreachgroup by category foreachcategory generate top10 URLs 46

64. Compilation in MapReduce Every group or join operation forms a map-reduce boundary Other operations pipelined into map and reduce phases load URL Info load Visits Map1 Map2 group by url Reduce1 foreachurl generate count join on url Reduce2 Map3 group by category Reduce3 foreachcategory generate top10 URLs 47

65. Data warehouse infrastructure built on top of Hadoop, providing: Data Summarization Ad hoc querying Simple query language: Hive QL (based on SQL) Extendable via custom mappers and reducers Subproject of Hadoop No „Hive format“ http://hadoop.apache.org/hive/ Hive 48

66. Hive - Example LOAD DATA INPATH `/data/visits` INTO TABLE visits INSERT OVERWRITE TABLE visitCounts SELECT url, category, count(*) FROM visits GROUP BY url, category; LOAD DATA INPATH ‘/data/urlInfo’ INTO TABLE urlInfo INSERT OVERWRITE TABLE visitCounts SELECT vc.*, ui.* FROM visitCountsvc JOIN urlInfoui ON (vc.url = ui.url); INSERT OVERWRITE TABLE gCategories SELECT category, count(*) FROM visitCounts GROUP BY category; INSERT OVERWRITE TABLE topUrls SELECT TRANSFORM (visitCounts) USING ‘top10’; 49

67. Higher level query language for JSON documents Developed at IBM‘s Almaden research center Supports several operations known from SQL Grouping, Joining, Sorting Built-in support for Loops, Conditionals, Recursion Custom Java methods extend JAQL JAQL scripts are compiled to MapReduce jobs Various I/O Local FS, HDFS, Hbase, Custom I/O adapters http://www.jaql.org/ JAQL 50

68. JAQL - Example registerFunction(„top“, „de.tuberlin.cs.dima.jaqlextensions.top10“); $visits= hdfsRead(„/data/visits“); $visitCounts= $visits -> groupby $url = $ into { $url, num: count($)}; $urlInfo= hdfsRead(„data/urlInfo“); $visitCounts= join $visitCounts, $urlInfo where $visitCounts.url == $urlInfo.url; $gCategories= $visitCounts -> group by $category = $ into {$category, num: count($)}; $topUrls= top10($gCategories); hdfsWrite(“/data/topUrls”, $topUrls); 51

69. Outline Query & Programming Model Logical Data Model Virtuali-zation Multi-Tenancy Service Level Agreements Storage Model DistributedStorage Replication Security 52

70. ACID vs. BASE Traditional distributeddatamanagement Web-scaledatamanagement ACID BasicallyAvailableSoft-stateEventualconsistent Strongconsistency Isolation Focus on „commit“ Availability? Pessimistic Difficultevolution (e.g. schema) Weakconsistency Availabilityfirst Best effort Optimistic (aggressive) Fast and simple Easierevolution 53

71. CAP Theorem [Brewer 2000] Consistency: all clientshavethesameview, even in case of updates Availability: all clients find a replica of data, even in thepresence of failures Tolerance to networkpartitions: systemproperties hold evenwhenthenetwork (system) ispartitioned Youcanhave at mosttwoof thesepropertiesforanyshared-data system. 54

72. CAP Theorem No consistencyguarantees➟ updateswithconflictresolution On a partitionevent, simplywaituntildataisconsistentagain➟ pessimisticlocking All nodesare in contactwitheachotherorputeverything in a single box➟ 2 phasecommit 55

73. CAP: Explanations PA :=update(o) PB:=read(o) 1. 3. 2. M Networkpartitions ➫ M isnotdelivered Solutions? Synchronousmessage: <PA,M> isatomic Possiblelatencyproblems (availability) Transaction <PA, M, PB>: requires to controlwhen PBhappens Impacts partitiontoleranceoravailability 56

74. Consistency Models [Vogels 2008] A B C update: D0->D1 read(D) D0 Distributedstoragesystem Strongconsistency: afterthe update completes, anysubsequentaccessfrom A, B, C will return D1 Weakconsistency: doesnotguaranteethatsubsequentaccesses will returnD1 -> a number of conditionsneed to bemetbeforeD1 isreturned Eventualconsistency: Special form of weakconsistency Guaranteesthatif no newupdatesaremade, eventually all accesses will returnD1 57

75. Variations of EventualConsistency Causalconsistency: If A notifies B aboutthe update, B will read D1 (butnot C!) Read-your-writes: A will alwaysread D1afteritsown update Session consistency: Read-your-writesinside a session Monotonicreads: If a process has seenDk, anysubsequentaccess will neverreturnany Diwith i < k Monotonicwrites: guarantees to serializethewrites of thesameprocess 58

77. Allowsreplicas to diverge; requiresconflictresolution

78. Allowdatabeaccessedwithouta-priorisynchronization

79. Updates arepropagated in thebackground

80. Occasionalconflictsarefixedaftertheyhappen

81. Improvedavailability, flexibility, scalabability, butsee CAP theorem59

82. OptimisticReplication: Elements 1 2 2 2 2 1 1 1 1 2 2 2 1 1 1. operationsubmission 3. scheduling 2. propagation 1+2 1+2 1+2 4. conflictresolution 5. commitment 60 Y. Saito, M. Shapiro: OptimisticReplication, ACM ComputingSurveys, 5(3):1-44, 2005

84. Updates pass throughthesystemlikeinfectiousdiseases

85. Pairwisecommunication: a sitecontactsothers (randomlychosen) and sends ist information, e.g. aboutupdates

86. All sitesprocessmessages in thesame way

87. Proactivebehaviour: no failurerecoverynecessary!

90. Deadlineconstraints

91. Percentileconstraints

92. fees, penalties, ...Common understandingaboutservices, guarantees, responsibilities 63 Application Server / middleware DBMS OS / Hardware

93. TechniquesforQoS in Data Management 64 Providesufficientresources Capacityplanning: „Howmuchboxesforcustomer X?“ Cost vs. Performance tradeoff Shielding Dedicated (virtual) systemforcustomers Scalability? Costefficiency? Scheduling Orderingrequests on priority At whichlevel?

94. Workload Management Purpose: achieveperformancegoalsforclasses of requests (queries, transactions) Resourceprovisioning Aspects: Specification of service-levelobjectives Workloadclassification and modeling Admissioncontrol & scheduling Staticpriorization: DB2 Query Patroller, Oracle Resource Manager, ... Goal-orientedapproaches Economicapproaches Utility-basedapproaches 65

95. Workload Characteristics Functional I/O requirements (volume, bandwidth) CPU Degree of parallelism Response times? Throughput? … Non-Functional Availability Reliability Durability Scalability … 66

96. WLM: Model classes workload classification MPL result admission control &scheduling transaction response time Admission control: limit the number of simultanously executing requests (multiprogramming level = MPL) Scheduling: ordering requests by priority 67

98. Explorespace of alternative mappings (searchproblem)

99. Runtimemonitoring and controlutility response time 68 Kephart, Das: Achievingself-management via utilityfunctions. IEEE Internet Computing 2007

101. Calculate job coordinates in query plan projectionbased on job featurevector

102. Inferjob‘scoordinates on theperformanceprojection69

103. Outline Query & Programming Model Logical Data Model Virtuali-zation Multi-Tenancy Service Level Agreements Storage Model DistributedStorage Replication Security 70

104. OverviewandChallenges outsourcing Data Pre- processor Private informationretrieval / Access privacy Data Owner queries Data confiden- tiality/ privacy Query Engine Query Pre/Post- processor queryresults User Completenessandcorrectness Service Provider (un-trusted) 71

105. Challenges I – Data Confidentiality/ Privacy Need to store data in the cloud But we do not trust the service providers for sensitive information encrypt the data and store it but still be able to run queries over the encrypted data do most of the work at the server Two issues Privacy during transmission (wells studied, e.g. through SSL/TLS) Privacy of stored data Querying over encrypted data is challenging needs to maintain content information on the server side, e.g. rangequeriesrequire order preserving data encryption mechanisms privacyperformancetradeoff 72

106. Query Processing on Encrypted Data Metadata server-side query Query Translator original query Query Engine Temporary Result client-side query encrypted results result Query Executor User Service Provider (un-trusted) Client Site 73

107. Executing SQL over Encrypted Data Hacigumus et al., (SIGMOD 2002) Main Steps Partition sensitive domains Order preserving: supportscomparison Random: query rewriting becomes hard Rewritequeries to targetpartitions Execute queries and return results Prune/post-processresults on client Privacy-Precision Trade-off Larger segments/partitions  increasedprivacy  decreasedprecision  increasedoverheads in query processing 74

109. Create a coarse index for each (or selected) attribute(s) in the original table75

112. Challenges II – Private Information Retrieval (PIR) User queries should be invisible to service provider More formal database is modeled as a string x of length N stored at remote server user wants to retrieve the bit xi for some i without disclosing any information about i to the server Paradox imagine buying in a store without the seller knowing what you buy X i x1, x2, …, xn xi User 77

113. Information-Theoretic 2-server PIR a1 = xl l ϵQ1 Q1∈{1,…,n} i n Service Provider 1 0 0 1 1 0 0 1 1 1 0 0 0 Q2=Q1 i i l ϵQ2 xi = a1 a2 Service Provider 2 User + + + + a2 = xl 78

114. Conclusion & Outlook CurrentInfrastructures MS Azure Amazon RDS + SimpleDB Amazon Dynamo Google BigTable Yahoo! PNUTS Conclusion Challenges & Trends 79

115. Current Solutions one DB for all clients one DB per client AmazonSimpleDB / Dynamo Amazon RDS Yahoo! PNUTS Google Bigtable,Cassandra, Voldemort Amazon S3 Microsoft SQL Azure Virtualization Replication DistributedStorage 80

116. Microsoft SQL Azure Cloud databaseserviceforAzureplatform Allows to create SQL server = group of databasesspreadacross multiple physicalmachines (incl. geo-location) Supports relational model and T-SQL (tables, views, indices, triggers, storedprocedures) Deployment and administrationusing SQL Server Management Studio Currentlimitations Individualdatabasesize = max. 10 GB No supportfor CLR, distributedqueries & transactions, spatialdata 81

117. Microsoft SQL Azure: Details Databases implemented as replicateddatapartitions Across multiple physicalnodes Provideloalbalancing and failover API SQL, ADO.NET, ODBC Tabular Data Streams SQL Server Authentication Sync Framework Prices 1 GB database: $9.99/month, 10 GB: $99.99/month + datatransfer SLA: 99.9% availability 82

119. Partition key: usedforassigningentities to partitions; Rowkey: unique ID within a partition

120. Sort order: singleindex per table

121. Atomictransactionswithin a partition83

122. Amazon RDS Amazon Relational Database Services Web Service to set up and operate a MySQLdatabase Full-featuredMySQL 5.1 Automateddatabasebackup Java-basedcommandlinetools and Web Service API forinstanceadministration Native DB access Prices: Small DB instance (1.7 GB memory, 1 ECU): $0.11/hour Largest DB instance (68 GB, 26 ECU): $3.10/hour + $0.10 GB-monthstorage + datatransfer 84

123. Amazon Data Services Amazon Simple Storage Service (S3) DistributedBlobstorageforobjects (1 Byte ... 5 GB data) REST-basedinterface to read, write, and deleteobjectsidentifiedbyunique, user-definedkey Atomicsingle-keyupdates; no locking Eventualconsistency (partiallyread-after-write) Aug 2009: morethan 64 billionobjects AmazonSimpleDB (= Amazon Dynamo???) Distributedstructuredstorage Web Service API foraccess Eventualconsistency 85

125. Restricted to a singledomain

126. SFWsyntax + count() + multi-attributepredicates

127. Onlystring-valueddata: lexicographicalcomparisons86

128. Amazon Dynamo Highlyavailable and scalablekey-valuedatastorefortheAmazonplatform Managesthestate of Amazonservices Providingbestsellerlists, shoppingcarts, customerpreferences, productcatalogs -> requireonlyprimary-keyaccess (e.g. productid, customerid) Completelydecentralized, minimal needformanualadministration (e.g. partitioning, redistribution) Assumptions: Simple querymodel: put/getoperations on keys, smallobjects (< 1MB) Weakerconsistencybut high availability („alwayswritable“ datastore), no isolationguarantees Efficiency: running on commodityhardware, guaranteedlatency = SLAs, e.g. 300 ms response time for 99.9% of requests, peakload of 500 requests/sec. 87

129. Dynamo: Partitioning and Replication Partitioningscheme based on consistenthashing Virtualnodes: eachphysicalnodeisresponsibleformorethanonevirtualnode Replication Eachdataitemisreplicated at n nodes A Key space = ring B E Responsibility ofnode C C Replicas of keys Fromrange (B,C) D 88

130. Dynamo: Data Versioning Provideseventualconsistency -> asynchronouspropagation of updates Updates result in a newversion of thedata Vector clocksforcapturingcausalitiesbetween different versions of thesameobject Vector clock = list of (node, counter) Determinecausalordering/parallelbranches of versions Update requestshave to specifywhichversionis to beupdated Reconciliationduringclientreads! reconcile(D)@NA write(D)@NB write(D)@NA write(D)@NA D3([NA,2],[NB,1]) D1([NA,1]) D2([NA,2]) D5([NA,3],[NB,1],[NC,1]) write(D)@NC D4([NA,2],[NC,1]) 89

131. Dynamo: Replicamaintenance Consistencyamongreplicas: Quorum protocol: R nodesmustparticipate in a read, W nodes in a write; R + W > N Sloppyquorum: Read/writesareperformed on thefirst N healthynodes Preference list: list of nodeswhichareresponsibleforstoring a givenkey For highestavailability: W=1 Replicasynchronization Anti-entropy: Merkle trees: hashtreeswhereleavesarehashes of keys, non-leavesarehashes of children Ifhashvalues of twonodesareequal, no need to check children 90

132. Google BigTable Fast and large-scale DBMS for Google applications and services Designed to scaleinto PB range Usesdistributed Google File System (GFS) forstoringdata and log files Depends on a clustermanagementsystemformanagingresource, monitoringstates, scheduling, .... Canbeused as inputsource and outputtargetforMapReduceprograms 91

133. BigTable: Data Model Bigtable = sparse, distributed, multi-dimensional sortedmap Indexedbyrowkey, columnkey, timestamp; value = array of bytes Rowkeys up to 64 KB; columnkeysgrouped in columnfamilies Timestamp (64 bitint) usedforversioning Data ismaintained in lexicographic order byrowkeys Rowrangeisdynamicallypartitioned ➪ tablet = unit of distribution and loadbalancing Read/writeopsunder a singlerowkeyareatomic value columnkey rowkey t1 t2 92

134. BigTable: System Architecture Single-masterdistributedstoragesystem masterserverresponsiblefor Assigningtablets to tabletservers Loadbalancing on tabletservers Detectingaddition and expiration of tabletservers Garbagecollection of GFS files Tabletservers Manage sets of tablets (10...1000 tablets per server, 100..200 MB per tablet) Handle read/writerequests Split tables Distributed, persistentlock/nameserviceChubby usesPaxosforreplicaconsistency (5 replicas) Providesnamespaceconsisting of directories and files; allowsdiscovering of tabletservers 93

135. BigTable: Tablets Internallystored in SSTables Immutable, sortedfile of key-valuepairs; organized in 64KB blocks + index (block ranges) TabletLocation Chubbycontainslocation of roottablet Roottabletcontainslocation of all tablets in a METADATA table METADATA tabletcontainslocation of usertablets + end keyrow (sparseindex) Three-levelschemeaddresses 234tablets Cachedbyclientlibrary User tables METADATA tablet Roottablet Chubbyfile 94

136. BigTable: Tablets /2 TabletAssignment Startingtabletserversacquire an exclusive lock in Chubby -> allowsdiscovery of tabletservers Periodicallychecksbythemaster on the lock status of tabletservers Replication of dataperformedby GFS TabletServing Updates (mutations) arelogged and thenapplied to an in-memoryversion (memtable) Compactions ConvertmemtableintoSSTable MergeSSTables 95

137. Yahoo! PNUTS Yahoo!‘sdataservingplatform Data & querymodel: Simple relational model: tables of recordswithattributes (incl. Blobtypes) Flexible schemaevolutionbyaddingattributes at any time Queries: single-tableselection & projection Updates & deletionsbased on primary-keyaccess Storagemodel: Records as parsed JSON objects Filesystem-basedhashtablesorMySQLInnoDBengine 96

138. PNUTS Architecture Clients REST API Tablet controller Routers Message Broker Storage units 97

139. PNUTS: Consistency & Replication Consistencymodel: Per-recordtimelineconsistency: all replicasapply all updates in thesame order User-specificguarantees: ready-any, read-latest, read-newer-than, writes, write-after-version Partitioning and replication: Tableshorizontallypartionedintotablets (100 MB ...10 GB) Eachserverisresponsiblefor 100+ tables Asynchronousreplicationbyusingmessagebroker (publish/subscribe) Guarantees delivery of messages (incl. Logging) Provides partial ordering of messages Record-levelmembership + mastership-migrationprotocol 98

140. Comparison 99

141. Conclusion DBaaS = outsourcingdatabases to reduce TCO Reduce operational / administrationcosts Pay as yougomodel Widespectrum of solutions „rent a database“ Cloud databases Usecases Database hosting Hostedservices Large-scaledataanalytics 100

143. Limitingfunctionality: SQL vs. put/getoperations

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149. Who has thefirstquestion? 105 ? wolfgang.lehner@tu-dresden.dekus@tu-ilmenau.de