Consistency Requester for Transactional Backup
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Solution Overview
Problem
Creating a backup of a system with resources involved in transactions often results in inconsistent data due to the snapshot of storage, as it may capture an image with incomplete or inconsistent transaction states.
Innovation Solution
A consistency requester is used to manage transactions, allowing those in a problematic state to exit while preventing new transactions from entering such states until all are resolved, enabling a consistent view of resources to be obtained and used for backup purposes, which can then be released, allowing transactions to re-enter problematic states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a shadow copy is created of storage involved in transactions, then a backup can be made quickly, but the backup data becomes inconsistent
Solution Approach 1:
The system performs preliminary actions by preventing transactions from entering problematic states before the shadow copy is created. The consistency requester blocks transactions that would create inconsistent states, ensuring that when the shadow copy is taken, all transactions are in valid states, thus guaranteeing backup consistency without sacrificing speed.
2Reliability
If transactions are blocked to ensure consistency, then backup consistency is achieved, but system productivity decreases
Solution Approach 1:
The system applies partial blocking by only preventing transactions from entering problematic states rather than blocking all transactions. The consistency requester allows transactions to proceed freely as long as they don't create inconsistent states, blocking only the specific problematic cases. This selective approach maintains high transaction throughput while ensuring backup consistency.
3Reliability
If transactions in problematic state are allowed to exit, then consistency can be achieved, but time is lost waiting for transactions to complete
Solution Approach 1:
The system implements feedback by continuously monitoring transaction states and dynamically adjusting blocking decisions. The consistency requester receives feedback from the transaction manager about which transactions are in problematic states and adjusts its blocking behavior accordingly. This real-time feedback mechanism allows the system to achieve consistency as quickly as possible by only blocking when necessary, minimizing wait time while ensuring reliable consistent views.
Data Source
AI summary
Aspects of the subject matter described herein relate to transactions. In aspects, a consistency requester such as a shadow copy service requests to have a consistent view of a set of resources. In response, transactions that are in a problematic state are allowed to exit the problematic state while new and existing transactions that are not in the problematic state are allowed to perform any work except work that takes them into the problematic state. After no transactions are in the problematic state, a consistent view of the set of resources is available. This view may be used by the consistency requester as desired. Afterwards, the consistency requester may indicate that a consistent view is no longer needed. Transactions are then allowed to enter the problematic state. Transactions may also be allowed to enter the problematic state if a timeout elapses.