oracle對(duì)象定義(英文版)-資料下載頁(yè)
2025-02-05 07:35本頁(yè)面
【正文】 a is written to segmentn Each extent supports multiple transactionsn Each transaction writes to its own block(s)n If extent fills, automatically extendsn If all extents fill, segment wrapsn If segment wraps, undo data overwrittenn If undo data not available, error occurs“Snapshot too old”“Cannot allocate extent”Copyright 169。 2023 Global Business Solutions, Inc.Read Consistencyn When query executes:l Current time determinedl Blocks with same time readl Newer blocks reconstructed with rollback segmentsCustomers Name Address…1 Acme Inc. 123 Ch2 Zachary’s 1234 Br3 Marie’s 4456 Si4 Chimney 9024 FSELECT * FROM customerUPDATE customer . . .Copyright 169。 2023 Global Business Solutions, Inc.Temporary Segmentsn Provide temporary workspacen Created automatically for joins, indexes, sortsn Created on disk when memory fulln Sized by DEFAULT STORAGE clause of tablespacen Reclaimed by SMONBootstrapSegmentRollbackSegmentIndexSegment Temporary SegmentCopyright 169。 2023 Global Business Solutions, Inc.Bootstrap Segmentn Contains dictionary definitions loaded on openn Is not user accessiblen Resides in SYSTEM tablespacen Requires no DBA maintenanceBootstrapSegmentRollbackSegmentIndexSegmentBootstrap SegmentCopyright 169。 2023 Global Business Solutions, Inc.Database Extentsn Consist of a set of contiguous blocksn Serve as space allocation for segmentn Deallocated when segment is removedn First extent created as Initial Extentn Grow by Next ExtentSegmentExtentExtentExtentCopyright 169。 2023 Global Business Solutions, Inc.Database Blocksn Are:l smallest unit of storagel sized by DB_BLOCK_SIZEl same as buffer in database buffer cachen Correspond to O/S blockn Typically sized as 2k, 4k, 8k, or 16kSegmentExtentBlocksCopyright 169。 2023 Global Business Solutions, Inc.Define Database Objects Summaryn Tablespaces are logical collections of database objects with one or more datafilesn Upon creation, space is preallocated for tablespacesTablespaceTables, indexes, etc. DatafilesSegmentExtentBlocksCopyright 169。 2023 Global Business Solutions, Inc.Define Database Objects Summaryn Segments are preallocated when objects createdn Segments consist of extentsn Extents are a set of contiguous blocksn As data is added, segments fill upn Storage management is essentialDataSegmentCustomers Name Address…1 Acme Inc. 123 Ch2 Zachary’s 1234 Br3 Marie’s 4456 Si4 Chimney 9024 FCopyright 169。 2023 Global Business Solutions, Inc.演講完畢，謝謝觀看
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