Why do we use nested transactions?

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BlackTom AI · Accepted Answer

Question: Why do we use nested transactions?

Option 1: 'Because many transactions have subcomponents that may fail and alternate decisions can be made about them rather than throwing away all the work of the whole transaction.' This is correct. Nested transactions allow partial commits or rollbacks within subcomponents, so if a subcomponent encounters an issue, you can roll back only that part without discarding the entire transaction, preserving work that succeeded.

Option 2: 'Because many transactions use nested loop join types and thus writing transactions this way makes optimisation easier.' This is misleading. Nested loop joins are a database join method, not a direct reason for using nested transactions. The statement confuses query execution strategies with transaction control mechanisms, so it does not accurately explain the purpose of nested transactions.

Option 3: 'Because many transactions can take locks easily' This is vague and not correct as a rationale. Nested transactions are not defined by ease of obtaining locks; rather, they provide a structured way to manage partial work and rollback semantics within a larger transaction. The claim about locks being easy to take does not address the fundamental motivation for nested transactions.

Option 4: 'Because many transactions are written by different people and each programmer writes one part of it.' Collaboration in development is a concern in software engineering, but it is not the primary transactional motivation for nested transactions. Nested transactions are about error containment and partial rollback within a single logical transaction, not about dividing work among developers.

Summary reasoning: The core purpose of nested transactions is to allow subcomponents of a larger transaction to succeed or fail independently, enabling partial commits or rollbacks. The other options misattribute the concept to join optimization, locking difficulty, or team organization, which do not capture the transactional semantics that nested transactions provide.

COMP90050_2025_SM2 Quiz 3

Why do we use nested transactions?

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