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ARIES Overview. xactionTable. dirtyPgTable. Checkpoint. 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. Disk. ARIES Overview. xactionTable.

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aries overview
ARIES Overview

xactionTable

dirtyPgTable

Checkpoint

  • 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

Disk

aries overview2
ARIES Overview

xactionTable

dirtyPgTable

Checkpoint

  • 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

Disk

  • 3 phases
    • Analysis
aries overview3

Analysis

checkpoint

Redo

redoLSN

Undo

Min(SOTlosers)

ARIES Overview

xactionTable

dirtyPgTable

Checkpoint

  • 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

Disk

  • 3 phases
    • Analysis
    • Redo
undo with clr
UNDO with CLR

Losers: 3

why physiological
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