天網搜索平臺PARADISE

天網搜索平臺PARADISE閆宏飛北京大學計算機系網絡實驗室2009/4/24信息檢索前沿概述閆宏飛北京大學計算機系網絡實驗室2009/4/24345OutlineIssues:searchengineandwebminingGoal:FrameworkPrinciples:Relatedcomponents(照應任務各部分關聯)Implementation:Achievements（應用成果）Casestudy（具體到一事）6SearchEngineandWebMiningCrawlingFull-textindexingRetrievingWebarchivingandMining7WebGraph:bowtieteapotModel:bagofwordsInfomall,CDAL:archivehistraceEvaluation:manualautomaticPlatform:proprietaryopen89OutlineMotivationtoBuildPARADISEDesignandImplementPARADISEResearchIssuesofConcern10Corpus(1/3)Shakespeare’scollectedworksAgzippedtar-file[2039k]http://www.cs.su.oz.au/~matty/Shakespeare/shakespeare.tar.gzRCV1,ReutersCorpusVolume1.oneyearofReutersnewswire1996-08-20to1997-08-19containsabout810,000ReutersEnglishLanguageNewsstories.requiresabout2.5GBforstorageoftheuncompressedfiles./data/reuters/reuters.html

11Corpus(2/3)CWT100GB,ChineseWebTestcollection2004年6月搜集，有5,712,710個網頁，解壓容量為90GB。CWT200GB2005年11月搜集，有37,482,913個網頁，壓縮容量為197GB/12Corpus(3/3)2008/10/1513Hardwareassumptionssymbol statistic values averageseektime 5ms=5x10?3sb transfertimeperbyte 0.02μs=2x10?8s processor’sclockrate 10?9sp lowleveloperation 0.01μs=10?8s(e.g.,compare&swapaword) sizeofmainmemory severalGB sizeofdiskspace 1TBormore14ReutersRCV1statisticssymbol statistic valueN documents 800,000L avg.#tokensperdoc 200M terms(=wordtypes) 400,000avg.#bytespertoken 6(incl.spaces/punct.)avg.#bytespertoken 4.5(withoutspaces/punct.)avg.#bytesperterm 7.5tokens 100,000,0004.5bytesperwordtokenvs.7.5bytesperwordtype:why?15DocumentsareparsedtoextractwordsandthesearesavedwiththeDocumentID.IdidenactJuliusCaesarIwaskilledi'theCapitol;Brutuskilledme.Doc1SoletitbewithCaesar.ThenobleBrutushathtoldyouCaesarwasambitiousDoc2Indexconstruction16KeystepAfteralldocumentshavebeenparsed,theinvertedfileissortedbyterms.Wefocusonthissortstep.Wehave100Mitemstosort.17ScalingindexconstructionIn-memoryindexconstructiondoesnotscale.Howcanweconstructanindexforverylargecollections?TakingintoaccountthehardwareconstraintsMemory,disk,speedetc.18Sort-basedIndexconstructionAswebuildtheindex,weparsedocsoneatatime.Whilebuildingtheindex,wecannoteasilyexploitcompressiontricks(youcan,butmuchmorecomplex)Thefinalpostingsforanytermareincompleteuntiltheend.At12bytesperpostingsentry,demandsalotofspaceforlargecollections.T=100,000,000inthecaseofRCV1So…wecandothisinmemoryin2008,buttypicalcollectionsaremuchlarger.E.g.NewYorkTimesprovidesindexof>150yearsofnewswireThus:Weneedtostoreintermediateresultsondisk.19Usethesamealgorithmfordisk?Canweusethesameindexconstructionalgorithmforlargercollections,butbyusingdiskinsteadofmemory?No:SortingT=100,000,000recordsondiskistooslow–toomanydiskseeks.Weneedanexternalsortingalgorithm.20BottleneckParseandbuildpostingsentriesonedocatatimeNowsortpostingsentriesbyterm(thenbydocwithineachterm)Doingthiswithrandomdiskseekswouldbetooslow–mustsortT=100MrecordsIfeverycomparisontook2diskseeks,andNitemscouldbesortedwithNlog2Ncomparisons,howlongwouldthistake?2112-byte(4+4+4)records(term,doc,freq).Thesearegeneratedasweparsedocs.Mustnowsort100Msuch12-byterecordsbyterm.DefineaBlock~10MsuchrecordsCaneasilyfitacoupleintomemory.Willhave10suchblockstostartwith.Basicideaofalgorithm:Accumulatepostingsforeachblock,sort,writetodisk.Thenmergetheblocksintoonelongsortedorder.BSBI:Blockedsort-basedIndexing(Sortingwithfewerdiskseeks)22BSBI:Blockedsort-basedIndexing23Remainingproblemwithsort-basedalgorithmOurassumptionwas:wecankeepthedictionaryinmemory.Weneedthedictionary(whichgrowsdynamically)inordertoimplementatermtotermIDmapping.Actually,wecouldworkwithterm,docIDpostingsinsteadoftermID,docIDpostings......butthenintermediatefilesbecomeverylarge.(Wewouldendupwithascalable,butveryslowindexconstructionmethod.)24SPIMI:

Single-passin-memoryindexingKeyidea1:Generateseparatedictionariesforeachblock–noneedtomaintainterm-termIDmappingacrossblocks.Keyidea2:Don’tsort.Accumulatepostingsinpostingslistsastheyoccur.Withthesetwoideaswecangenerateacompleteinvertedindexforeachblock.Theseseparateindexescanthenbemergedintoonebigindex.25

SPIMI-InvertMergingofblocksisanalogoustoBSBI.26DistributedindexingForweb-scaleindexing(don’ttrythisathome!):mustuseadistributedcomputingclusterIndividualmachinesarefault-proneCanunpredictablyslowdownorfailHowdoweexploitsuchapoolofmachines?27GoogledatacentersGoogledatacentersmainlycontaincommoditymachines.Datacentersaredistributedaroundtheworld.Estimate:atotalof1millionservers,3millionprocessors/cores(Gartner2007)Estimate:Googleinstalls100,000serverseachquarter.Basedonexpendituresof200–250milliondollarsperyearThiswouldbe10%ofthecomputingcapacityoftheworld!?!28GoogledatacentersIfinanon-fault-tolerantsystemwith1000nodes,eachnodehas99.9%uptime,whatistheuptimeofthesystem?Answer:37%Calculatethenumberofserversfailingperminuteforaninstallationof1millionservers.29DistributedindexingMaintainamastermachinedirectingtheindexingjob–considered“safe”.Breakupindexingintosetsof(parallel)tasks.Mastermachineassignseachtasktoanidlemachinefromapool.30ParalleltasksWewillusetwosetsofparalleltasksParsersInvertersBreaktheinputdocumentcorpusintosplitsEachsplitisasubsetofdocuments(correspondingtoblocksinBSBI/SPIMI)31ParsersMasterassignsasplittoanidleparsermachineParserreadsadocumentatatimeandemits(term,doc)pairsParserwritespairsintojpartitionsEachpartitionisforarangeofterms’firstletters(e.g.,a-f,g-p,q-z)–herej=3.Nowtocompletetheindexinversion32InvertersAninvertercollectsall(term,doc)pairs(=postings)foroneterm-partition.Sortsandwritestopostingslists33DataflowsplitsParserParserParserMastera-fg-pq-za-fg-pq-za-fg-pq-zInverterInverterInverterPostingsa-fg-pq-zassignassignMapphaseSegmentfilesReducephase34MapReduceTheindexconstructionalgorithmwejustdescribedisaninstanceofMapReduce.MapReduce(DeanandGhemawat2004)isarobustandconceptuallysimpleframeworkfordistributedcomputingwithouthavingtowritecodeforthedistributionpart.TheydescribetheGoogleindexingsystem(ca.2002)asconsistingofanumberofphases,eachimplementedinMapReduce.35MapReduceIndexconstructionwasjustonephase.Anotherphase:transformingaterm-partitionedindexintodocument-partitionedindex.Term-partitioned:onemachinehandlesasubrangeoftermsDocument-partitioned:onemachinehandlesasubrangeofdocumentsmostsearchenginesuseadocument-partitionedindex…betterloadbalancing,etc.36SchemaforindexconstructioninMapReduceSchemaofmapandreducefunctionsmap:input→list(k,v)reduce:(k,list(v))→outputInstantiationoftheschemaforindexconstructionmap:webcollection→list(termID,docID)reduce:(<termID1,list(docID)>,<termID2,list(docID)>,…)→(postingslist1,postingslist2,…)Exampleforindexconstructionmap:d2:Cdied.d1:Ccame,Cc’ed.→(<C,d2>,<died,d2>,<C,d1>,<came,d1>,<C,d1>,<c’ed,d1>reduce:(<C,(d2,d1,d1)>,<died,(d2)>,<came,(d1)>,<c’ed,(d1)>)→(<C,(d1:2,d2:1)>,<died,(d2:1)>,<came,(d1:1)>,<c’ed,(d1:1)>)37有幾個問題需要解決很難找到合適的硬件設施，基于這些數據開展工作存儲，運行，維護，….缺少處理這些數據的有效的軟件工具分析，檢索，評測，….如何維護有stateofarts算法的軟件工具模塊替換，功能測試，性能測試，…38智能中文搜索引擎技術研究及平臺構建由一個平臺,四個任務組成的.達到平臺能夠展示四個任務.平臺是:一個開放式智能化中文搜索引擎平臺任務是:構建適用于中文互聯網的文本內容抽取系統(tǒng)及網頁文本內容結構化分析基于內容的多媒體信息檢索基于自然語言理解的查詢分析基于用戶屬性挖掘的個性化檢索/src/paradise/39PARADISEDesign

PlatformforApplying,ResearchingAndDevelopingIntelligentSearchEngineServersServersServersServersServersServersServersServersServersServersServersServersServersServersServersServersServersServersServersServersServersBareMetalMachinesAutomationClusterManagementToolsDatanodesTianwangjobsandevaluationjobs40PARADISE索引設計介紹41當前設計中的基本功能Usingfastersingle-passindexingHighlycompressedindexdiskdatastructuresVariouscompressalgorithm(*)Variousinvertindexfileformat(*)indexposition,freqvalueorimpactvalue(*)Indexfieldinformation,suchastitle,dateCachesupport(*)42下一步設計的功能Indexvariousdocumentformat，suchasword,pdf使用MapReduce等技術的索引多種切詞的實現與處理增量索引與文檔刪除Termvector存儲多segment的合并策略43InvertedindexDocument-sortedindexThepointersineachinvertedlistarestoredinincreasingdocumentorderUsingd-gapFrequency-sortedindexInvertedlistarestoredindecreasingtermfrequencyscoreImpact-sortedindexThepointersareorderedaccordingtotheimpactvalueImpactvalueisasmallintegerrepresentingtheoverallcontributionoftermttothescoreofdocumentd,includethefactorusedtonormalizefordocumentlength44ProcessingquerymodeDocument-at-a-timeAllinvertedlistsaresimultaneouslyaccessed|q|-wayprocessingiscarriedouttohandleaqueryqof|q|termsTerm-at-a-timeOnlyoninvertedlistisaccessedatanygiventimeAsequenceof|q|-1binaryoperationsareperformedNotclearbetterthandocument-at-a-timeprocessingScore-at-a-timeAllofthetermlistsareopenforreadingProcessedindecreasingscorecontributionorderratherthaninincreasingdocumentnumberorderDynamicquerypruning45IndexlevelsDocumentnumbersonlyOnlysupportBooleanqueriesDocumentnumbersandScoreScorecanbeimpactscoresorfrequentorbothSupportBooleanandrankedqueriesDocumentnumbers,Score,PositionsSupportBoolean,ranked,phrase(proximityqueries)46TypesofindexandsupportquerymodestypedsposOrganizationProcessingmodesupportedDY--Document-sortTermordoc–at-a-timeDSYY-Document-sortImpactorfreq-sortTermordoc–at-a-timeDSPYYYDocument-sortedTermordoc-at-a-timescore-at-a-time47InterleavingPointerinterleavingEachdocumentnumberisimmediatelyfollowedbythecorrespondingworfvalueorposvalueTerminterleavingKeepvariousrelatedpartsofeachinvertedlistincontiguousblocsNon-interleavingUsingseparateinvertedfileEachstoringaparticulartypeofinformationFordistinctdiskpointersmaintainedineachentryinthedictionary48Block-interleavedindexesEachinvertedlistisbuiltupasasequenceofoneormoregroupsWithineachgrouptherearefourormorek-blocks49Cache是一個工具包，為一些模塊提供cache功能Cahce策略與存儲分開有多種cahce策略 當前實現MRU策略多種存儲策略基于STLmap采用模板實現，保證其通過性50DocumentThelogicalrepresentationofaDocumentforindexingandsearchingADocumentisacollectionofFieldablesAFieldableisalogicalrepresentationofauser'scontentthatneedstobeindexedorstoredFieldableshaveanumberofpropertiesthattelltheindexhowtotreatthecontent(likeindexed,tokenized,stored,etc.)51Compress工具包，提供整形數字的解壓縮實現多種解壓縮算法采用工廠方法模式52AnalysisAnanalyzerbuildsTokenStreams,whichanalyzetextItthusrepresentsapolicyforextractingindextermsfromtextTypicalimplementationsfirstbuildaTokenizer,whichbreaksthestreamofcharactersintorawTokensOneormoreTokenFiltersmaythenbeappliedtotheoutputoftheTokenizer53PARADISEImplementation

/src/paradise/

applicationPKUsearchpdfliteraturesearch2008Olympicssearchmodulecrawlanalysis&indexsearchutilitycompressBuffer...thirdpartycmake,boost,zlib,tidy,openssl,berkeleydbdataTianwangFormatquerylogIPLocator

tutorialCMakeandBoostreferenceBooksandpaperscourseInformationRetrievalCloudComputingDistributedSy