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CS 632 Lecture 6 Recovery

CS 632 Lecture 6 Recovery. Principles of Transaction-Oriented Database Recovery Theo Haerder, Andreas Reuter, 1983. ARIES: A Transaction Recovery Method Supporting Fine-Granularity Locking and Partial Rollbacks Using Write-Ahead Logging C. Mohan, Don Haderle,

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CS 632 Lecture 6 Recovery

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  1. CS 632 Lecture 6 Recovery Principles of Transaction-Oriented Database Recovery Theo Haerder, Andreas Reuter, 1983 ARIES: A Transaction Recovery Method Supporting Fine-Granularity Locking and Partial Rollbacks Using Write-Ahead Logging C. Mohan, Don Haderle, Bruce Lindsay, Hamid Piralesh, and Peter Schwartz, 1992

  2. Principles of Transaction-Oriented Database Recovery • DATABASE RECOVERY: WHAT IT IS EXPECTED TO DO • What Is a Transaction • Which Failures Have To Be Anticipated • Summary of Recovery Actions • THE MAPPING HIERARCHY OF A DBMS • The Mapping Process • The Storage Hierarchy • Different Views of a Database • Mapping Concepts for Updates • CRASH RECOVERY • Dependencies Between Buffer Management and Recovery Component • Classification of Log Data • Checkpoints • ARCHIVE RECOVERY

  3. What is a transaction? • actions executed indivisibly • four properties required (the ACID properties): • Atomicity: • all actions in the transaction happen, or none happen • Consistency: • if a transaction preserves the consistency of the DB • Isolation: • execution of one transaction is isolated from that of other transactions • Durability: • if a transaction commits, its effects persist

  4. Which Failures Have to Be Anticipated? Transaction Failures: • caused by bad input or other violations of consistency System Failures: • caused by: • bugs in the DBMS code • operating system fault • hardware failure • occur less frequently Media Failures: • caused by: • software errors • hardware errors • physical errors

  5. Summary of Recovery Actions • Transaction Undo • when a transaction aborts itself • Global Undo • when recovering from a system failure • incomplete transactions • Partial Redo • when recovering from a system failure • complete transactions • Global Redo • archive recovery • full redundancy

  6. Different Views of a Database • Current database • the contents are found on disk or in the DB buffer • Materialized database • the state that the DBMS finds at restart after a crash • Physical database • all blocks of the on-line copy • Three types of update operations: • modification of page contents – affects the current database • write – affects the physical database • propagation – affects the materialized database

  7. Mapping Concepts for Updates Two schemes for propagation: • Two types of propagation strategies: • ATOMIC • NOT ATOMIC

  8. Dependencies Between Buffer Management and Recovery Component • UNDO Recovery Actions: • STEAL – undo actions necessary • NO STEAL – undo actions not necessary • REDO Recovery Actions: • FORCE – redo actions not necessary • NO FORCE – redo actions necessary • Partial REDO: no logging necessary • Global REDO: logging necessary

  9. Classification of Log Data • Physical State Logging on Page Level • before image – after image • Physical Transition Logging on Page Level • differences between old and new states • Physical State Logging on Access Path Level • Physical/Logical Transition Logging on the Access Path • Logical Logging on the Record-Oriented Level

  10. Checkpoints • limit the amount of REDO recovery required after a crash • involve three steps: • write a BEGIN_CHECKPOINT record • write all checkpoint data • write an END_CHECKPOINT record • types: • Transaction-Oriented Checkpoints • Transaction-Consistent Checkpoints • Action-Consistent Checkpoints • Fuzzy Checkpoints

  11. Conclusion • taxonomy for classifying the implementation techniques for • database recovery • four criteria: • Propagation • ATOMIC/ NOT ATOMIC • Buffer Handling • STEAL / NO STEAL • EOT Processing • FORCE / NO FORCE • Checkpointing

  12. ARIES: A Transaction Recovery Method Supporting Fine-Granularity Locking and Partial Rollbacks Using Write-Ahead Logging ARIES – Algorithm for Recovery and Isolation Exploiting Semantics

  13. Goals • Simplicity • Operation logging • Flexible storage management • Partial rollbacks • Flexible buffer management • Recovery Independence • Logical undo • Parallelism and fast recovery • Minimal overhead

  14. Normal Processing • Updates • Total or Partial Rollbacks • savepoints • Transaction Termination • Checkpoints • fuzzy checkpoints Restart Processing • Analysis Pass • Redo Pass • Undo Pass

  15. Log Records • LSN (Log Sequence Number) • unique id for each log record • Type • type of record • TransId • id of transaction that wrote the record • PrevLSN • LSN of the previous log record written by the same • transaction that wrote the record • PageID • id of the page referred by the log • UndoNextLSN • present in CLR • Data • redo/undo data describing the update

  16. Page Structure • page_LSN – the LSN of the log record describing the latest • update to the page Transaction Table • TransId – the id of the transaction • State • LastLSN • UndoNextLSN Dirty Pages Table • PageId • RecLSN

  17. Restart Processing • Analysis Pass • Redo Pass • Undo Pass • Selective or Deferred Restart

  18. Media Recovery • fuzzy image copy (fuzzy archive dump) • image copy checkpoint • media recovery redo point Nested Top Actions • top actions • nested top actions

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