Questions and Answers
What is the primary purpose of Strict Two-phase Locking (Strict 2PL) protocol in transaction management?
What must happen if a transaction Ti is aborted?
During which phase of the Aries recovery algorithm are dirty pages updated in the buffer pool?
What triggers the release of a transaction's locks in a DBMS according to the content?
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Why is it essential to write log records to disk before the changed page in transaction management?
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Study Notes
Transaction Management Overview
- Anomalies can occur during interleaved execution, particularly with uncommitted data.
- Types of conflicts include Overwriting Uncommitted Data, often represented as WW Conflicts.
Lock-Based Concurrency Control
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Strict Two-phase Locking Protocol (Strict 2PL):
- Requires obtaining a shared (S) lock before reading and an exclusive (X) lock before writing.
- Locks are released only when the transaction completes.
- No other transaction can obtain any lock on an object held under an exclusive lock.
- Ensures only serializable schedules.
Aborting a Transaction
- When a transaction (Ti) is aborted, all its changes must be undone.
- If another transaction (Tj) reads data last written by Ti, Tj also must be aborted to maintain consistency.
- Systems typically prevent cascading aborts by keeping locks until a transaction commits.
- Transactions can only read data written by another transaction after the latter commits.
Logging Mechanism
- A log records every write action of a transaction to facilitate rollback and system recovery.
- Log entries for writes include both the old and new values.
- Commit and abort actions of transactions are also recorded in the log.
- Log records must first be written to disk before changes to the actual data.
Log Structure and Recovery
- Log records are linked by transaction IDs, simplifying the undo process.
- Logs are often duplicated and stored in stable storage for reliability.
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Aries Recovery Algorithm Phases:
- Analysis Phase: Scans the log from the last checkpoint to identify active transactions and dirty pages.
- Redo Phase: Reapplies updates to dirty pages in the buffer pool to ensure data consistency.
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Description
Explore the intricacies of transaction management in Database Management Systems with a focus on anomalies that occur from interleaved execution. This quiz covers concepts such as overwriting uncommitted data and the strict two-phase locking protocol. Test your understanding of these critical mechanisms in ensuring data consistency and integrity.