吉林大学大型数据库设计与实现dba-09.ppt

StorageStructureandRelationships

ObjectivesAftercompletingthislesson,youshouldbeabletodothefollowing:DescribethelogicalstructureofthedatabaseListthesegmenttypesandtheirusesListthekeywordsthatcontrolblockspaceusageObtaininformationaboutstoragestructuresfromthedatadictionaryListthecriteriaforseparatingsegments

OverviewDatabaseLogicalPhysicalTablespaceDatafileOSblockOracle

blockSegmentExtent

TypesofSegmentsTableClusterTable

partitionIndex

TypesofSegmentsIndex-organized

tableIndex

partitionUndo

segmentTemporary

segment

TypesofSegmentsLOB

segmentBootstrap

segmentNestedtable

StorageClausePrecedenceOracledefaultTablespaceSegment

ExtentAllocationandDeallocationAllocatedwhenthesegmentis:CreatedExtendedAlteredDeallocatedwhenthesegmentis:DroppedAlteredTruncated

UsedandFreeExtentsDatafileFreeextentUsedextentFileheader

DatabaseBlockMinimumunitofI/OConsistsofoneormoreOSblocksSetattablespacecreationDB_BLOCK_SIZEisthedefaultblocksize

DatabaseBlockContentsHeaderFreespaceData

BlockSpace

UtilizationParametersINITRANSMAXTRANSPCTFREEPCTUSED

DataBlockManagementTwomethodsareavailableformanagingdatablocks:AutomaticSegment-SpaceManagementManualConfiguration

AutomaticSegment-Space

ManagementItismethodofmanagingfreespaceinsidedatabasesegmentsTrackingin-segmentfreeandusedspaceisdoneusingbitmapsasopposedtofreelistsThismethodprovides:EaseofmanagementBetterspaceutilizationBetterperformanceforconcurrentINSERToperationsRestriction:CannotbeusedfortablespaceswhichwillcontainLOBs.

AutomaticSegment-Space

ManagementBitmapsegmentscontainabitmapthatdescribesthestatusofeachblockinthesegmentwithrespecttoitsavailablespace.Themapiscontainedinaseparatesetofblocksreferredtoasbitmappedblocks(BMBs).Wheninsertinganewrow,theserversearchesthemapforablockwithsufficientspace.Astheamountofspaceavailablei