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Materi Pendukung Pertemuan <<8>> Media pemulihan kerusakan

Materi Pendukung Pertemuan <<8>> Media pemulihan kerusakan. Matakuliah : <<M0264>>/<<Sistem Manajemen Basis Data>> Tahun : <<2006>> Versi : <<1/1>>. Basic Idea: Logging. Record REDO and UNDO information, for every update, in a log . Sequential writes to log (put it on a separate disk).

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Materi Pendukung Pertemuan <<8>> Media pemulihan kerusakan

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  1. Materi Pendukung Pertemuan <<8>>Media pemulihan kerusakan Matakuliah : <<M0264>>/<<Sistem Manajemen Basis Data>> Tahun : <<2006>> Versi : <<1/1>>

  2. Basic Idea: Logging • Record REDO and UNDO information, for every update, in a log. • Sequential writes to log (put it on a separate disk). • Minimal info (diff) written to log, so multiple updates fit in a single log page. • Log: An ordered list of REDO/UNDO actions • Log record contains: <XID, pageID, offset, length, old data, new data> • and additional control info (which we’ll see soon).

  3. Write-Ahead Logging (WAL) • The Write-Ahead Logging Protocol: • Must force the log record for an update before the corresponding data page gets to disk. • Must write all log records for a Xact beforecommit. • #1 guarantees Atomicity. • #2 guarantees Durability. • Exactly how is logging (and recovery!) done? • We’ll study the ARIES algorithms.

  4. DB RAM LSNs pageLSNs flushedLSN pageLSN WAL & the Log • Each log record has a unique Log Sequence Number (LSN). • LSNs always increasing. • Each data pagecontains a pageLSN. • The LSN of the most recent log record for an update to that page. • System keeps track of flushedLSN. • The max LSN flushed so far. • WAL:Before a page is written, • pageLSN £ flushedLSN Log records flushed to disk “Log tail” in RAM

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