Pre-write Transaction Execution Model
The Pre-write Transaction Execution Model is a concurrency control technique used in mobile databases to improve transaction efficiency, especially under intermittent connectivity and limited resources.
Concept Overview:
In the Pre-write model, updates from a transaction are not immediately written to the database. Instead, they are pre-written or tentatively stored in a separate buffer or log. These changes remain invisible to other transactions until the transaction successfully commits.
Key Steps in Pre-write Execution:
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Transaction Starts: A mobile user initiates a transaction.
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Pre-write Phase: Updates are recorded in a temporary storage (like a pre-write buffer or local cache), not in the main database.
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Validation: Before committing, the system validates whether the transaction can proceed without violating consistency rules.
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Commit: Once validated, the pre-written data is flushed to the main database, making the changes visible.
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Rollback (if needed): If validation fails, the transaction is aborted, and the pre-writes are discarded.
Benefits in Mobile Databases:
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Reduced Locking Overhead: Since updates are delayed, fewer locks are held, increasing concurrency.
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Better Performance Offline: Supports tentative execution of transactions during disconnection.
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Conflict Minimization: Changes are applied only after validation, reducing inconsistencies.
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Resource Efficiency: Suits mobile devices with limited bandwidth and processing power.
Conclusion:
The Pre-write model enhances transaction efficiency in mobile environments by supporting tentative, low-overhead execution and resolving conflicts before final commitment, which is crucial in mobile systems where reliability and availability are often compromised.
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