Immediate Database Modification The immediate-modification scheme allows updates of an uncommitted transaction to be made to the buffer,or the disk itself. before the transaction commits Update log record must be written before database item is written We assume that the log record is output directly to stable storage (Will see later that how to postpone log record output to some extent)） Output of updated blocks to stable storage can take place at any time before or after transaction commit Order in which blocks are output can be different from the order in which they are written. The deferred-modification scheme performs updates to buffer/disk only at the time of transaction commit Simplifies some aspects of recovery But has overhead of storing local copy Database System Concepts-6th Edition 16.13 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 16.13 ©Silberschatz, Korth and Sudarshan th Edition Immediate Database Modification The immediate-modification scheme allows updates of an uncommitted transaction to be made to the buffer, or the disk itself, before the transaction commits Update log record must be written before database item is written We assume that the log record is output directly to stable storage (Will see later that how to postpone log record output to some extent) Output of updated blocks to stable storage can take place at any time before or after transaction commit Order in which blocks are output can be different from the order in which they are written. The deferred-modification scheme performs updates to buffer/disk only at the time of transaction commit Simplifies some aspects of recovery But has overhead of storing local copy