基于authorware的交互课件的设计与制作

《基于authorware的交互课件的设计与制作》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、TheHadoopDistributedFilesystemWhenadatasetoutgrowsthestoragecapacityofasinglephysicalmachine,itbecomesnecessarytopartitionitacrossanumberofseparatemachines.Filesystemsthatmanagethestorageacrossanetworkofmachinesarecalleddistributedfilesystems.Sincetheyarenetwork-based,allthecomplicationsofne

2、tworkprogrammingkickin,thusmakingdistributedfilesystemsmorecomplexthanregulardiskfilesystems.Forexample,oneofthebiggestchallengesismakingthefilesystemtoleratenodefailurewithoutsufferingdataloss.HadoopcomeswithadistributedfilesystemcalledHDFS,whichstandsforHadoopDistributedFilesystem.(Youmays

3、ometimesseereferencesto“DFS”—informallyorinolderdocumentationorconfiguration—whichisthesamething.)HDFSisHadoop’sflagshipfilesystemandisthefocusofthischapter,butHadoopactuallyhasageneralpurposefilesystemabstraction,sowe’llseealongthewayhowHadoopintegrateswithotherstoragesystems(suchasthelocal

4、filesystemandAmazonS3).TheDesignofHDFSHDFSisafilesystemdesignedforstoringverylargefileswithstreamingdataaccesspatterns,runningonclustersoncommodityhardware.Let’sexaminethisstatementinmoredetail:Verylargefiles“Verylarge”inthiscontextmeansfilesthatarehundredsofmegabytes,gigabytes,orterabytesin

5、size.ThereareHadoopclustersrunningtodaythatstorepetabytesofdata.*StreamingdataaccessHDFSisbuiltaroundtheideathatthemostefficientdataprocessingpatternisawrite-once,read-many-timespattern.Adatasetistypicallygeneratedorcopiedfromsource,thenvariousanalysesareperformedonthatdatasetovertime.Eachan

6、alysiswillinvolvealargeproportion,ifnotall,ofthedataset,sothetimetoreadthewholedatasetismoreimportantthanthelatencyinreadingthefirstrecord.CommodityhardwareHadoopdoesn’trequireexpensive,highlyreliablehardwaretorunon.It’sdesignedtorunonclustersofcommodityhardware(commonlyavailablehardwareavai

7、lablefrommultiplevendors†)forwhichthechanceofnodefailureacrosstheclusterishigh,atleastforlargeclusters.HDFSisdesignedtocarryonworkingwithoutanoticeableinterruptiontotheuserinthefaceofsuchfailure.ItisalsoworthexaminingtheapplicationsforwhichusingHDF