Defining global transactions In a distributed DBMS, a “global transaction” is best described as one where:

Introduction / Context:Transactions define units of atomic work. In distributed databases, a transaction may touch data at multiple sites. Such a transaction must be coordinated to ensure ACID properties across nodes, typically through a transaction manager and protocols like two-phase commit (2PC).

Given Data / Assumptions:

• The database is distributed across networked sites.
• The transaction's read/write set may include fragments at remote sites.
• The DDBMS provides routing and commit coordination.

Concept / Approach:

A global (or distributed) transaction accesses at least one nonlocal site. The DDBMS decomposes the query/updates into subtransactions, executes them at the right sites, and coordinates commit/rollback. If everything is local, it is not “global.” If the DDBMS refuses to route, it cannot satisfy cross-site data access, contradicting the definition.

Step-by-Step Solution:

Verification / Alternative check:

Most DDBMS textbooks classify transactions as local (single site) or global/distributed (multiple sites), with 2PC ensuring atomic outcomes across participants.

Why Other Options Are Wrong:

• Options a/c: describe local-only transactions.
• Option d: contradicts routing beyond local; then it isn't truly distributed.
• Option e: cross-site commit typically requires coordination (e.g., 2PC).

Common Pitfalls:

• Ignoring partial failures and network partitions in design of global transactions.

Final Answer:

Some required data are at one or more nonlocal sites and the DDBMS routes requests across sites as needed.