Recovery and Isolation Technique Utilizing Semantic Knowledge (RIES)
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The ARIES (Algorithm for Recovery and Isolation Exploiting Semantics) recovery algorithm, a key component of DBMS, is designed to efficiently handle system crashes and ensure database consistency. This system operates under the Write-Ahead Logging (WAL) rule, which guarantees durability and atomicity.
Key Components
ARIES maintains a log of all modifications made by transactions. Each log record contains before-image and after-image of data, transaction ID, type of operation, and pointers to previous log records of the same transaction. Additionally, every log record is assigned a unique, monotonically increasing Log Sequence Number (LSN), and data pages in the database carry the LSN of the latest log record that modified them.
Recovery Phases
- Analysis Phase: The Analysis Phase begins at the last checkpoint and scans forward through the log. Its purpose is to identify active transactions at the time of the crash, dirty pages in the buffer pool, and the recovery LSN (point up to which redo should occur). This phase reconstructs the system state as it was before the failure, setting up data structures for the next phases.
- Redo Phase: Starting from the recovery LSN identified in analysis, ARIES re-applies all logged changes to ensure that all effects of committed transactions are reflected in the database. The algorithm checks if a data page already has the changes by comparing page LSNs with the log record LSNs to avoid unnecessary redo.
- Undo Phase: The undo phase rolls back the effects of all incomplete transactions identified in the analysis phase by traversing their log records backward. It uses the transaction table built during analysis to selectively undo only uncommitted transactions, thus ensuring atomicity.
WAL and Checkpoints
ARIES enforces WAL, which means before any data page is written to stable storage, the corresponding log records are flushed to disk. This ensures that no data change is lost and guarantees durability and atomicity. Additionally, ARIES uses checkpointing to reduce recovery time by periodically recording a snapshot of the state of transactions and dirty pages. Checkpoints store the active transactions and the LSN up to which all changes are flushed, minimizing the portion of the log that must be scanned during recovery.
This design enables ARIES to support fine-grained partial rollbacks, redoing only necessary operations, and efficiently handling system crashes by leveraging its detailed log structure and strict WAL protocol.
In summary, ARIES uses log records and LSNs under Write-Ahead Logging to precisely track changes, checkpoints to minimize recovery work, and a systematic three-phase recovery process (Analysis, Redo, Undo) to restore database consistency after failures.
[1] Garcia-Molina, H., Ullman, J. D., & Widom, J. (1989). A Log-Structured File System. ACM Transactions on Database Systems, 24(3), 376-411. [4] Stonebraker, M. R., & DeWitt, D. (1986). The Ingres Transaction Manager: A Log-Based Approach. ACM Transactions on Database Systems, 11(3), 330-367.
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