What is Concurrency Control?
Concurrency control ensures that multiple transactions can run simultaneously without causing data inconsistency or conflicts.
Why Concurrency Control?
- To avoid lost updates
- To maintain database consistency
- To avoid temporary inconsistency
- To ensure isolation
Concurrency Problems
- Lost Update: Two transactions overwrite each other’s changes.
- Dirty Read: Reading uncommitted data.
- Unrepeatable Read: Data changes between reads.
- Phantom Read: New rows appear during a transaction.
Concurrency Control Techniques
- Locking Mechanisms: Shared & exclusive locks
- Two-Phase Locking (2PL): Growing & shrinking phases
- Timestamp Ordering
- Validation-Based Protocols
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