DP-900 Practice Question: Identify considerations for relational data on Azure
A hospital uses Azure SQL Database to store patient records. The database contains tables for patient information, insurance details, and treatment plans. The system must ensure that if a transaction updates a patient's insurance and their treatment plan in two separate rows, either both updates succeed or both fail. Which ACID property guarantees this behavior?
⚠ Common exam trap
It's easy for candidates to confuse atomicity with consistency, thinking that consistency alone ensures all-or-nothing updates, but consistency only enforces rules and constraints—it is atomicity that provides the rollback mechanism to prevent partial transactions.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Atomicity
Atomicity ensures that a transaction is treated as a single, indivisible unit of work. In Azure SQL Database, if a transaction updates both the insurance and treatment plan rows, atomicity guarantees that either both updates are committed or both are rolled back, preventing partial updates that could leave data in an inconsistent state.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Durability
Why it's wrong here
Durability, as an ACID property, guarantees that once a transaction is committed, its changes persist even after a system crash or power loss, primarily through write-ahead logs and database snapshots in Azure SQL Database. However, it does not handle the scenario where one UPDATE statement succeeds and the next fails within the same uncommitted transaction—durability only applies after a commit, so it cannot ensure the all-or-nothing update of both patient record rows.
- ✗
Consistency
Why it's wrong here
Consistency enforces database rules such as constraints, triggers, and foreign keys to ensure a transaction transforms the database from one valid state to another, preventing data that violates integrity rules. Yet consistency alone does not guarantee that all operations within a transaction complete together; if a partial update occurs before a later error, the database might temporarily violate consistency until the transaction is rolled back, which is precisely the job of atomicity.
- ✗
Isolation
Why it's wrong here
Isolation controls how concurrently executing transactions interact, using mechanisms like row-level locking or snapshot isolation in Azure SQL Database to prevent dirty reads or lost updates. It does not provide any mechanism to automatically undo partial modifications within the same transaction if a later statement fails; isolation operates between transactions, not within a single transaction, so it cannot ensure that both rows are updated or neither is updated.
- ✓
Atomicity
Why this is correct
Atomicity is the ACID property that treats a transaction as an indivisible unit: all statements inside it must succeed, or the entire transaction is aborted and any already-applied changes are rolled back to the original state. In Azure SQL Database, atomicity is implemented via the transaction log and rollback operations—if the second UPDATE of the patient record fails, the first UPDATE is undone, ensuring that the two rows are always updated together. This directly fulfills the hospital's requirement that both rows be updated or neither, regardless of where the failure occurs.
Go deeper
Related to this question
Learn chapter
Data Roles and Core Concepts
Key term
Data
Data is raw, unprocessed information, like numbers, words, or measurements, that can be stored, processed, and analyzed by computers.
Key term
Azure SQL Database
Azure SQL Database is a fully managed relational database-as-a-service (DBaaS) in Microsoft Azure, based on the SQL Server engine, that handles scaling, backups, patching, and high availability automatically.
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