Oracle引航课程第7章 数据库对象（二）.pdf

DATAGURU专业数据分析网站 2012.10.15 数据库引航 第七课Oracle数据库对象（二）DATAGURU专业数据分析网站 2012.10.15重做日志 -REDODATAGURU专业数据分析网站 2012.10.15REDODATAGURU专业数据分析网站 2012.10.15REDO-日志组DATAGURU专业数据分析网站 2012.10.15REDO和归档DATAGURU专业数据分析网站 2012.10.15REDO的内容-改变向量DATAGURU专业数据分析网站 2012.10.15REDO -undo的redoDATAGURU专业数据分析网站 2012.10.15UNDO作用 数据的回滚 一致性读 表的闪回（事务，查询的闪回.) 失败会话的恢复DATAGURU专业数据分析网站 2012.10.15Undo的产生DATAGURU专业数据分析网站 2012.10.15Undo V.S. RedoInconsistent reads in multiuser systemsUndo segmentsRollback, read consistency, flashbackHow to undo a changeUndoProtects againstStored inUsed forRecord ofRolling forward database changesRedo log filesData lossHow to reproduce a changeRedoRedo log filesUndo egmnt1-11 Copyright Oracle Corporation, 2002. All rights reserved.Redo Buffer OperationWhen user entersUser #1UPDATE emp SET sal = 10 WHERE id = 1234database buffer cache data file 2 data file 4undo file 31234 5 XYZZack1-12 Copyright Oracle Corporation, 2002. All rights reserved.Redo Buffer OperationWhen user entersUser #1UPDATE emp SET sal = 10 WHERE id = 1234The data block is retrieved from disk to the database buffer cache (unless itsalready there)1234 5database buffer cache data file 2 data file 4undo file 31234 5 XYZZack1-13 Copyright Oracle Corporation, 2002. All rights reserved.Redo Buffer OperationWhen user entersUser #1UPDATE emp SET sal = 10 WHERE id = 1234The data block is retrieved from disk to the database buffer cache (unless itsalready there)1234 5The undo block is then retrieved from disk to the database buffer cache (unless its already there)U1database buffer cache data file 2 data file 41234 5 XYZZackundo file 31-14 Copyright Oracle Corporation, 2002. All rights reserved.Redo Buffer OperationWhen user entersUser #1UPDATE emp SET sal = 10 WHERE id = 1234The data block is retrieved from disk to the database buffer cache (unless itsalready there)1234 5The undo block is then retrieved from disk to the database buffer cache (unless its already there)U1database buffer cache data file 2 data file 4The undo data iscreated showing the before image51234 5 XYZZackundo file 31-15 Copyright Oracle Corporation, 2002. All rights reserved.Redo Buffer OperationWhen user entersUser #1UPDATE emp SET sal = 10 WHERE id = 1234The data block is retrieved from disk to the database buffer cache (unless itsalready there)1234 5The udo block is then retrieved from disk to the database buffer cache (unless its already there)U1database buffer cache data file 2 data file 4The undo data iscreated showing the before image5And an entry recording this change is made in the REDO bufferRedo BufferTran File Block Row Column Value idT1 3 12 - - 51234 5 XYZZackundo file 31-16 Copyright Oracle Corporation, 2002. All rights reserved.Redo Buffer OperationWhen user entersUser #1UPDATE emp SET sal = 10 WHERE id = 12341234 5U1database buffer cache data file 2 data file 45Redo BufferTran File Block Row Column Value idT1 3 12 - - 51234 5 XYZZackThen the data block ischanged. x10undo file 31-17 Copyright Oracle Corporation, 2002. All rights reserved.Redo Buffer OperationWhen user entersUser #1UPDATE emp SET sal = 10 WHERE id = 12341234 5U1database buffer cache data file 2 data file 45Redo BufferTran File Block Row Column Value idT1 3 12 - - 51234 5 XYZZackThen the data block ischanged. x10And an entry recording this change is made in the REDO bufferT1 2 123 41 6 10undo file 3DATAGURU专业数据分析网站 2012.10.15Undo 表空间普通的数据表空间机制和数据表空间完全一致，只不过用途不同。DATAGURU专业数据分析网站 2012.10.15自动管理回滚段表空间动态改变回滚段的个数。自动调整回滚段的大小DATAGURU专业数据分析网站 2012.10.15Undo数据的保留时间DATAGURU专业数据分析网站 2012.10.15Undo表空间的损坏如果有活动的事务，需要恢复Undo表空间，如果没有备份，将导致数据库损坏。如果没有活动事务，可以重建一个undo表空间。DATAGURU专业数据分析网站Thanks FAQ时间