吉林大学大型数据库设计与实现dba-07.ppt

MaintainingRedoLogFiles

ObjectivesAftercompletingthislesson,youshouldbeabletodothefollowing:ExplainthepurposeofonlineredologfilesOutlinethestructureofonlineredologfilesControllogswitchesandcheckpointsMultiplexandmaintainonlineredologfilesManageonlineredologsfileswithOMF

UsingRedoLogFilesRedologfilesrecordallchangesmadetodataandprovidearecoverymechanismfromasystemormediafailure.Redologfilesareorganizedintogroups.AnOracledatabaserequires atleasttwogroups.Eachredologwithina groupiscalledamember.RedologfilesDatabase

StructureofRedoLogFilesGroup2Group3Group1MemberDisk1Disk2MemberMemberMemberMemberMember

HowRedoLogsWorkRedologsareusedinacyclicfashion.Whenaredologfileisfull,LGWRwillmovetothenextloggroup.ThisiscalledalogswitchCheckpointoperationalsooccursInformationiswrittentothecontrolfile

ForcingLogSwitchesandCheckpointsLogswitchescanbeforcedusingtheALTERSYSTEMSWITCHLOGFILEcommand.Checkpointscanbeforcedusing:SettingFAST_START_MTTR_TARGETparameterALTERSYSTEMCHECKPOINTcommandALTERSYSTEMCHECKPOINT;

log2b.rdolog1b.rdoAddingOnlineRedoLogGroupsGroup1Group2Group3ALTERDATABASEADDLOGFILEGROUP3($HOME/ORADATA/u01/log3a.rdo,$HOME/ORADATA/u02/log3b.rdo)SIZE1M;log3b.rdolog2a.rdolog3a.rdolog1a.rdo

AddingOnlineRedoLogMembersALTERDATABASEADDLOGFILEMEMBER$HOME/ORADATA/u04/log1c.rdoTOGROUP1,$HOME/ORADATA/u04/log2c.rdoTOGROUP2,$HOME/ORADATA/u04/log3c.rdoTOGROUP3;log2c.rdolog2a.rdoGroup1log1c.rdolog1b.rdolog1a.rdoGroup2log2c.rdolog2b.rdolog2a.rdoGroup3log3c.rdolog3b.rdolog3a.rdo

log2a.rdolog1a.rdoGroup1Group2Group3log3a.rdoDroppingOnlineRedo

LogGroupsALTERDATABASEDROPLOGFILEGROUP3;

log1a.rdolog1a.rdoDroppingOnlineRedo

LogMembersALTERDATABASEDROPLOGFILEMEMBER$HOME/ORADATA/u04/log3c.rdo;log2c.rdolog1c.rdoGroup1Group2log1b.rdolog1b.rdo

Clearing,Relocating,o