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 11/19/2018

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 11/19/2018

Atomicity: Consistency: Isolation: Durability: 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 11/19/2018

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: software errors hardware errors physical errors 11/19/2018

Summary of Recovery Actions Transaction Undo when a transaction aborts itself Global Undo when recovering from a system failure incomplete transactions Partial Redo complete transactions Global Redo archive recovery full redundancy 11/19/2018

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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 11/19/2018

Mapping Concepts for Updates Two schemes for propagation: Two types of propagation strategies: ATOMIC NOT ATOMIC 11/19/2018

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 11/19/2018

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 11/19/2018

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 11/19/2018

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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 11/19/2018

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ARIES – Algorithm for Recovery and Isolation Exploiting Semantics ARIES: A Transaction Recovery Method Supporting Fine-Granularity Locking and Partial Rollbacks Using Write-Ahead Logging ARIES – Algorithm for Recovery and Isolation Exploiting Semantics 11/19/2018

Goals Simplicity Operation logging Flexible storage management Partial rollbacks Flexible buffer management Recovery Independence Logical undo Parallelism and fast recovery Minimal overhead 11/19/2018

Normal Processing Restart Processing Updates Total or Partial Rollbacks savepoints Transaction Termination Checkpoints fuzzy checkpoints Restart Processing Analysis Pass Redo Pass Undo Pass 11/19/2018

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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 11/19/2018

Page Structure Transaction Table Dirty Pages Table 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 11/19/2018

Restart Processing Analysis Pass Redo Pass Undo Pass Selective or Deferred Restart 11/19/2018

Media Recovery Nested Top Actions fuzzy image copy (fuzzy archive dump) image copy checkpoint media recovery redo point Nested Top Actions top actions nested top actions 11/19/2018