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CS 415 Operating Systems Principles Logging and Recovery. Dr. Edward C. Cheng. Logging and Recovery. Background System Model of the Logging System A Disintegration Model of Activity Recording 2-Phase Commit Protocol Rollback Recovery.

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Presentation Transcript
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CS 415

Operating Systems Principles

Logging and Recovery

Dr. Edward C. Cheng

logging and recovery
Logging and Recovery
  • Background
  • System Model of the Logging System
  • A Disintegration Model of Activity Recording
  • 2-Phase Commit Protocol
  • Rollback Recovery
system model of journaling

Fig 1. With OJS, multiple data streams can be open per AP/RM

Fig 2. Data streams are managed through life-cycle states

System Model of Journaling
  • Tightly coupled with the resource manager or application program
  • Open Journal idea introduced in the 90’s separating journaling from the RM or AP
a disintegration model of activity recording
A Disintegration Model of Activity Recording
  • Events that are not dependent on each other can have their activity records disintegrated thus provide various optimization opportunities
2 phase commit 2pc protocol
2-Phase Commit (2PC) Protocol
  • A protocol to support Atomicity Behavior in distributive environment
  • A coordinator (parent transaction) issues a request to commit to all subordinates (children transactions)
  • Each subordinate writes a journal record to ensure ability to roll-forward and rollback in case of a crash
  • Each subordinate responds to the parent with a ready-to-commit or abort
  • If all subordinates are ready-to-commit, the coordinate issues a commit event to all subordinates (otherwise an abort event)
  • All subordinates commit their works
recovery
Recovery
  • Checkpoint – the point where all committed changes are flushed out to data pages
  • Undo record: enough information to rollback the change (insert, delete, update) – mainly before and after images
  • Redo record: enough information to re-execute un-flushed changes
  • Upon commit, only make sure to flush out the log records so that upon recovery (after a crash), the system can redo the changes
  • Changes might be flushed out to disk before commit. Locks are used to protect us from dirty read. Undo records help to undo uncommitted transactions upon recovery
  • Question: what if you have changes that cannot be undone?
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