testyahoo

yahoo 相册  时间:2021-02-22  阅读:()
AlternativeConcurrencyControlMethodsR&G-Chapter17RoadmapSofar:Correctnesscriterion:serializabilityLock-basedCCtoenforceserializabilityStrict2PLDeadlocksLockinggranularitiesTreelockingprotocolsPhantomsToday:AlternativeCCmechanismsOptimisticCC(Kung-Robinson)Lockingisaconservativeapproachinwhichconflictsareprevented.
Disadvantages:Lockmanagementoverhead.
Deadlockdetection/resolution.
Lockcontentionforheavilyusedobjects.
Lockingis"pessimistic"becauseitassumesthatconflictswillhappen.
WhatifconflictsarerareWemightgetbetterperformancebynotlocking,andinsteadcheckingforconflictsatcommittime.
Kung-RobinsonModelXactshavethreephases:READ:Xactsreadfromthedatabase,butmakechangestoprivatecopiesofobjects.
VALIDATE:Checkforconflicts.
WRITE:Makelocalcopiesofchangespublic.
RVWValidationIdea:testconditionsthataresufficienttoensurethatnoconflictoccurred.
EachXactassignedanumericid.
Justuseatimestamp.
AssignedatendofREADphase.
ReadSet(Ti):SetofobjectsreadbyXactTi.
WriteSet(Ti):SetofobjectsmodifiedbyTi.
Test1ForalliandjsuchthatTiWTS(O):AllowTtoreadO.
ResetRTS(O)tomax(RTS(O),TS(T))ChangetoRTS(O)onreadsmustbewrittentodisk!
Thisandrestartsrepresentoverheads.
TimestampCC:WhenXactTwantstoWriteObjectOIfTS(T)WTS(O))untilwriterofOcommits.
SimilartowritersholdingXlocksuntilcommit,butstillnotquite2PL.
T1T2W(A)R(A)W(B)CommitUnrecoverableschedulesareallowedbyTimestampCC!
Recoverableschedule:xactscommitonlyafter(andif)allxactswhosechangestheyreadcommitAweakerconditionthanAvoidCascadingRollbackMultiversionTimestampCCIdea:Letwritersmakea"new"copywhilereadersuseanappropriate"old"copy:OO'O''MAINSEGMENT(CurrentversionsofDBobjects)VERSIONPOOL(Olderversionsthatmaybeusefulforsomeactivereaders.
)Readersarealwaysallowedtoproceed.
Butmaybeblockeduntilwritercommits.
MultiversionCC(Contd.
)Eachversionofanobjecthasitswriter'sTSasitsWTS,andtheTSoftheXactthatmostrecentlyreadthisversionasitsRTS.
Versionsarechainedbackward;wecandiscardversionsthatare"toooldtobeofinterest".
EachXactisclassifiedasReaderorWriter.
Writermaywritesomeobject;Readerneverwill.
XactdeclareswhetheritisaReaderwhenitbegins.
ReaderXactForeachobjecttoberead:FindsnewestversionwithWTSReaderXactsareneverrestarted.
However,mightblockuntilwriteroftheappropriateversioncommits.
ToldnewWTStimelineWriterXactToreadanobject,followsreaderprotocol.
Towriteanobject:FindsnewestversionVs.
t.
WTSIfRTS(V))Else,rejectwrite.
ToldnewWTSCVVRTS(V)SummaryOptimisticCCusingend-of-xact"validation"Goodif:Read-dominatedworkloadSystemhaslotsofextraresourcesMostrealsystemsuselockingSummary(Contd.
)Anotheralternative:TimestampCCDecidelogicalxactexecutionorderwhenxactsentersystemEnforcebycomparingxacttimestampswithobjecttimestampsVariant:MultiversionCCKeepout-of-dateversionsofobjects,so"old"readersdon'thavetorestart(theycanrun"inthepast")OracleusesaflavorofmultiversionCC

香港E3-1230v2 16GB 30M 326元/月 数脉科技

官方网站:https://www.shuhost.com/公司名:LucidaCloud Limited尊敬的新老客户:艰难的2021年即将结束,年终辞旧迎新之际,我们准备了持续优惠、及首月优惠,为中小企业及个人客户降低IT业务成本。我们将持续努力提供给客户更好的品质与服务,在新的一年期待与您有美好的合作。# 下列价钱首月八折优惠码: 20211280OFF (每客户限用1次) * 自助购买可复制...

CloudCone2核KVM美国洛杉矶MC机房机房2.89美元/月,美国洛杉矶MC机房KVM虚拟架构2核1.5G内存1Gbps带宽,国外便宜美国VPS七月特价优惠

近日CloudCone发布了七月的特价便宜优惠VPS云服务器产品,KVM虚拟架构,性价比最高的为2核心1.5G内存1Gbps带宽5TB月流量,2.89美元/月,稳定性还是非常不错的,有需要国外便宜VPS云服务器的朋友可以关注一下。CloudCone怎么样?CloudCone服务器好不好?CloudCone值不值得购买?CloudCone是一家成立于2017年的美国服务器提供商,国外实力大厂,自己开...

HostKvm:夏季优惠,香港云地/韩国vps终身7折,线路好/机器稳/适合做站

hostkvm怎么样?hostkvm是一家国内老牌主机商家,商家主要销售KVM架构的VPS,目前有美国、日本、韩国、中国香港等地的服务,站长目前还持有他家香港CN2线路的套餐,已经用了一年多了,除了前段时间香港被整段攻击以外,一直非常稳定,是做站的不二选择,目前商家针对香港云地和韩国机房的套餐进行7折优惠,其他套餐为8折,商家支持paypal和支付宝付款。点击进入:hostkvm官方网站地址hos...

yahoo 相册为你推荐
google竞价排名谷歌竞价排名现在是显示在什么位置?真正免费的网络电话谁有真正免费的网络电话??无线路由器限速设置如何设置无线路由器局域网限速?中国论坛大全中国十大网站是?不兼容安卓手机软件不兼容怎么办?唱吧电脑版官方下载唱吧有没有电脑版的啊?唱吧电脑版官方下载电脑怎么安装唱吧,要能用的,请教教程,谢谢畅想中国用“心系祖国情,畅想中国梦”为题目的800字作文人人逛街人人逛街评论怎么不显示链接了?好像4月28日就不能显示了。是什么原因呢?商标注册查询官网商标注册网的官网是哪个?
广西虚拟主机 免费域名 看国外视频直播vps asp.net主机 java主机 cloudstack rak机房 好玩的桌面 howfile 七夕快乐英文 lol台服官网 512mb 空间登陆首页 网通服务器 supercache 阵亡将士纪念日 网络速度 rewritecond 小夜博客 新疆服务器 更多