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ARIES Overview

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ARIES Overview. 3 phases. Analysis. Reconstruct dirtyPg, xaction ... ARIES Overview. Redo. Replay log from redoLSN. Replay all updates -- 'Repeating History' ... – PowerPoint PPT presentation

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Title: ARIES Overview


1
ARIES Overview
xactionTable
dirtyPgTable
Checkpoint
Disk
  • 3 phases
  • Analysis
  • Reconstruct dirtyPg, xaction tables
  • Find redoLSN
  • Min(recLSN) in dirtyPgTable
  • Start from last checkpoint, scan forward
  • After analysis, conservative estimate of
    dirtyPgTable

2
ARIES Overview
xactionTable
dirtyPgTable
Checkpoint
Disk
  • 3 phases
  • Analysis
  • Redo
  • Replay log from redoLSN
  • Replay all updates -- Repeating History
  • Idempotent thanks to pageLSN
  • Optimizations that allow us to avoid some writes
  • Physical logging e.g., exact bytes, or
    byte-level diff

3
ARIES Overview
xactionTable
dirtyPgTable
Checkpoint
Disk
  • 3 phases
  • Analysis
  • Redo
  • Undo
  • Just undo losers
  • Xactions in the xaction table
  • Start at lastLSN, follow prevLSNs in the log
  • Logical UNDO -- e.g., Remove record i, pg k
  • Write CLRs as we go
  • Allow us to avoid multiple UNDOs

4
UNDO with CLR
Losers 3
5
UNDO with CLR
6
UNDO with CLR
7
UNDO with CLR
8
UNDO with CLR
9
UNDO with CLR
10
UNDO with CLR
11
UNDO with CLR
12
Why Physiological?
  • Why do we do physical REDO?
  • (Hint ARIES is !ATOMIC)
  • System not action consistent at crash
  • Why do we do logical UNDO?
  • More compact records
  • Physical layout may be different at UNDO time
  • E.g., suppose additional records in index since
    record was written
  • Why do we repeat history?
  • So that we can use physical REDO
  • If an action is redone, we have exactly the same
    layout on disk
  • pageLSN on disk lets us determine this
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