Flashback Technology Recovering from Logical CorruptionsWord文件下载.docx
- 文档编号:16634726
- 上传时间:2022-11-25
- 格式:DOCX
- 页数:19
- 大小:28.62KB
Flashback Technology Recovering from Logical CorruptionsWord文件下载.docx
《Flashback Technology Recovering from Logical CorruptionsWord文件下载.docx》由会员分享,可在线阅读,更多相关《Flashback Technology Recovering from Logical CorruptionsWord文件下载.docx(19页珍藏版)》请在冰豆网上搜索。
UndoaDROPTABLEOperation
∙OracleFlashbackDatabase:
AlternativetoPoint-In-TimeRecovery
∙UsingOracleFlashbackFeaturesTogetherinDataRecovery:
Scenario
OracleFlashbackTechnology:
Overview
OracleFlashbackTechnologyprovidesasetoffeaturesthatsupportviewingandrewindingdatabackandforthintime.Theflashbackfeaturesofferthecapabilitytoquerypastversionsofschemaobjects,queryhistoricaldata,analyzedatabasechanges,orperformself-servicerepairtorecoverfromlogicalcorruptionswhilethedatabaseisonline.
∙OracleFlashbackQueryfeatureletsyouspecifyatargettimeandthenrunqueriesagainstyourdatabase,viewingresultsastheywouldhaveappearedatthattime.Torecoverfromanunwantedchangelikeanerroneousupdatetoatable,ausercouldchooseatargettimebeforetheerrorandrunaquerytoretrievethecontentsofthelostrows.
∙OracleFlashbackVersionQueryletsyouviewalltheversionsofalltherowsthateverexistedinoneormoretablesinaspecifiedtimeinterval.Youcanalsoretrievemetadataaboutthedifferingversionsoftherows,includingstarttime,endtime,operation,andtransactionIDofthetransactionthatcreatedtheversion.Thisfeaturecanbeusedbothtorecoverlostdatavaluesandtoauditchangestothetablesqueried.
∙OracleFlashbackTransactionQueryletsyouviewchangesmadebyasingletransaction,orbyallthetransactionsduringaperiodoftime.
∙OracleFlashbackTablereturnsatabletoitsstateatapreviouspointintime.Youcanrestoretabledatawhilethedatabaseisonline,undoingchangesonlytothespecifiedtable.
∙OracleFlashbackDropreversestheeffectsofaDROPTABLEstatement.
∙OracleFlashbackDatabaseprovidesamoreefficientalternativetodatabasepoint-in-timerecovery.Whenyouuseflashbackdatabase,yourcurrentdatafilesreverttotheircontentsatapasttime.Theresultismuchliketheresultofapoint-in-timerecoveryusingdatafilebackupsandredologs,butyoudonothavetorestoredatafilesfrombackupandyoudonothavetore-applyasmanyindividualchangesintheredologsasyouwouldhavetodoinconventionalmediarecovery.
FlashbackTable,FlashbackQuery,FlashbackTransactionQueryandFlashbackVersionQueryallrelyonundodata,recordsoftheeffectsofeachupdatetoanOracledatabaseandvaluesoverwrittenintheupdate.UsedprimarilyforsuchpurposesasprovidingreadconsistencyforSQLqueriesandrollingbacktransactions,theseundorecordscontaintheinformationrequiredtoreconstructdataasitstoodatapasttimeandexaminetherecordofchangessincethatpasttime.
SeeAlso:
∙OracleDatabaseConceptsandOracleDatabaseAdministrator'
sGuideformoreinformationonundodataandautomaticundomanagement
∙"
OracleFlashbackDrop:
UndoaDROPTABLEOperation"
formoreinformationonFlashbackDropandtherecyclebin
∙OracleDatabaseApplicationDeveloper'
sGuide-FundamentalsformoreinformationonFlashbackQuery,FlashbackTransactionQueryandFlashbackVersionQuery
OracleFlashbackQuery:
RecoveringattheRowLevel
Inadatarecoverycontext,itisusefultobeabletoquerythestateofatableataprevioustime.If,forinstance,youdiscoverthatat12:
30PM,anemployee'
JOHN'
hadbeendeletedfromyourEMPLOYEEtable,andyouknowthatat9:
30AMthatemployee'
sdatawascorrectlystoredinthedatabase,youcouldquerythecontentsofthetableasofatimebeforethedeletiontofindoutwhatdatahadbeenlost,and,ifappropriate,re-insertthelostdatainthedatabase.
QueryingthepaststateofthetableisachievedusingtheASOFclauseoftheSELECTstatement.Forexample,thefollowingqueryretrievesthestateoftheemployeerecordfor'
at9:
30AM,April4,2003:
SELECT*FROMEMPLOYEEASOFTIMESTAMP
TO_TIMESTAMP('
2003-04-0409:
30:
00'
'
YYYY-MM-DDHH:
MI:
SS'
)
WHEREname='
;
RestoringJohn'
sinformationtothetableEMPLOYEErequiresthefollowingupdate:
INSERTINTOemployee
(SELECT*FROMemployeeASOFTIMESTAMP
);
Themissingrowisre-createdwithitspreviouscontents,withminimalimpacttotherunningdatabase.
sGuide-FundamentalsforamoreextensivediscussionoftheuseoftheSELECT...ASOFSQLstatementandextensiveexamplesofitsuse.
∙OracleDatabaseSQLReferenceformoredetailsonthesyntaxoftheSELECT...ASOFformoftheSELECTstatement.
OracleFlashbackTable:
ReturningIndividualTablestoPastStates
OracleFlashbackTableprovidestheDBAtheabilitytorecoveratableorsetoftablestoaspecifiedpointintimeinthepastveryquickly,easily,andwithouttakinganypartofthedatabaseoffline.Inmanycases,FlashbackTableeliminatestheneedtoperformmorecomplicatedpoint-in-timerecoveryoperations.FlashbackTablerestorestableswhileautomaticallymaintainingassociatedattributessuchascurrentindexes,triggersandconstraints,andnotrequiringtheDBAtofindandrestoreapplication-specificproperties.UsingFlashbackTablecausesthecontentsofoneormoreindividualtablestoreverttotheirstateatsomepastSCNortime.
FlashbackTableusesinformationintheundotablespacetorestorethetable.Thisprovidessignificantbenefitsovermediarecoveryintermsofeaseofuse,availabilityandfasterrestorationofdata.
FormoreinformationonAutomaticUndoManagement,seeOracleDatabaseAdministrator'
sGuide.
PrerequisitesforUsingFlashbackTable
TheprerequisitesforperformingaFLASHBACKTABLEoperationareasfollows:
∙YoumusthavebeengrantedtheFLASHBACKANYTABLEsystemprivilegeoryoumusthavetheFLASHBACKobjectprivilegeonthetable.
∙YoumusthaveSELECT,INSERT,DELETE,andALTERprivilegesonthetable.
∙UndoinformationretainedintheundotablespacemustgofarenoughbackintimetosatisfythespecifiedtargetpointintimeorSCNfortheFLASHBACKTABLEoperation.
∙RowmovementmustbeenabledonthetableforwhichyouareissuingtheFLASHBACKTABLEstatement.YoucanenablerowmovementwiththefollowingSQLstatement:
∙ALTERTABLEtableENABLEROWMOVEMENT;
PerformingFlashbackTable
ThefollowingSQL*PlusstatementperformsaFLASHBACKTABLEoperationonthetableemployee:
FLASHBACKTABLEemployeeTOTIMESTAMP
`YYYY-MM-DDHH24:
Theemployeetableisrestoredtoitsstatewhenthedatabasewasatthetimespecifiedbythetimestamp.
YoucanalsospecifythetargetpointintimefortheFLASHBACKTABLEoperationusinganSCN:
FLASHBACKTABLEemployeeTOSCN123456;
ThedefaultforaFLASHBACKTABLEoperationisfortriggersonatabletobedisabled.Thedatabasedisablestriggersforthedurationoftheoperation,andthenreturnsthemtothestatethattheywereinbeforetheoperationwasstarted.Ifyouwishforthetriggerstostayenabled,thenusetheENABLETRIGGERSclauseoftheFLASHBACKTABLEstatement,asshowninthisexample:
FLASHBACKTABLEt1TOTIMESTAMP'
2003-03-0312:
05:
ENABLETRIGGERS;
ThefollowingscenarioistypicalofthekindoflogicalcorruptionwhereFlashbackTablecouldbeused:
At17:
00anHRadministratordiscoversthatanemployee"
JOHN"
ismissingfromtheEMPLOYEEtable.Thisemployeewaspresentat14:
00,thelasttimesheranareport.Someoneaccidentallydeletedtherecordfor"
between14:
00andthepresenttime.SheusesFlashbackTabletoreturnthetabletoitsstateat14:
00,asshowninthisexample:
FLASHBACKTABLEEMPLOYEESTOTIMESTAMP
2003-04-0414:
00:
'
)
OracleDatabaseSQLReferenceforasimpleFlashbackTablescenario
UndoaDROPTABLEOperation
OracleFlashbackDropreversestheeffectsofaDROPTABLEoperation.Theintentionbehindthisfeatureistoprovideuserswitharecoverymechanismforanaccidentaldropofatable.FlashbackDropissubstantiallyfasterthanotherrecoverymechanisms(suchaspoint-in-timerecovery)andalsodoesnotleadtoanylossofrecenttransactions.
Whenyoudropatable,thedatabasedoesnotimmediatelyremovethespaceassociatedwiththetable.Instead,thetableisrenamedand,alongwithanyassociatedobjects,itisplacedintheRecycleBinofthedatabase.TheFlashbackDropoperationrecoversthetablefromtherecyclebin.
TounderstandhowtouseOracleFlashbackDrop,youmustalsounderstandhowtherecyclebinworks,andhowtoaccessandmanageitscontents.
Thissectioncoversthefollowingtopics:
∙WhatistheRecycleBin?
∙HowTablesandOtherObjectsArePlacedintheRecycleBin
∙NamingConventionforObjectsintheRecycleBin
∙ViewingandQueryingObjectsintheRecycleBin
∙RecycleBinCapacityandSpacePressure
∙PurgingObjectsfromtheRecycleBin
WhatistheRecycleBin?
Therecyclebinisalogicalcontainerforalldroppedtablesandtheirdependentobjects.Whenatableisdropped,thedatabasewillstorethetable,alongwithitsdependentobjectsintherecyclebinsothattheycanberecoveredlater.Dependentobjectswhicharestoredintherecyclebinincludeindexes,constraints,triggers,nestedtables,LOBsegmentsandL
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Flashback Technology Recovering from Logical Corruptions
链接地址:https://www.bdocx.com/doc/16634726.html