DP-900 Describe core data concepts Practice Question
A financial services company stores account balances in Azure SQL Database (strong consistency) and transaction audit logs in Azure Cosmos DB (eventual consistency by default). A compliance requirement demands that when a transaction is rolled back in the SQL database, the corresponding audit log entries in Cosmos DB must also be removed within a short time frame. Which term best describes the difficulty of maintaining this constraint?
⚠ Common exam trap
Candidates often confuse ACID compliance (which is a property of a single database) with the ability to maintain atomicity across multiple independent data stores, leading them to select Option A instead of recognizing the need for distributed transaction coordination.
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
✓
Distributed transaction coordination
The scenario requires coordinating a rollback across two distinct data stores—Azure SQL Database (ACID-compliant, strong consistency) and Azure Cosmos DB (eventual consistency by default). This cross-system transactional consistency is a classic distributed transaction coordination problem, often addressed via patterns like the two-phase commit (2PC) or the saga pattern, but not natively supported between these two services without custom orchestration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ACID compliance
Why it's wrong here
ACID compliance is a guarantee provided by an individual database engine for its own transactions—atomicity, consistency, isolation, and durability within that single system. When account balances live in separate or heterogeneous stores, no single ACID transaction spans them; each store might comply with ACID independently, but there is no global atomic commit. Achieving all-or-nothing behavior across those stores requires a distributed transaction manager or a saga-based compensation flow, not just reliance on each store's local ACID properties.
When this WOULD be correct
A question asking about the property that ensures a database transaction is all-or-nothing, such as 'Which property guarantees that a transaction in a relational database either fully completes or fully rolls back?'
- ✗
Idempotency
Why it's wrong here
Idempotency means that repeating the same operation (e.g., retrying a credit after a network timeout) produces the same outcome and does not apply the transaction twice. It protects against duplicate writes, but it does not make two separate writes in different stores atomic or roll back one if the other fails. Cross-store consistency requires a coordinator or a compensation flow, not just retry-safe handlers.
When this WOULD be correct
A question describing a system where a payment processing API must safely handle duplicate requests (e.g., due to network retries) without causing double charges. The correct answer would be idempotency, as the API should produce the same result regardless of how many times the request is sent.
- ✓
Distributed transaction coordination
Why this is correct
A financial transfer that debits one account and credits another touches two independent storage systems. Distributed transaction coordination—via a two-phase commit or a saga pattern with compensating actions—ensures atomicity across those stores, so a failure in one step does not leave a partial, inconsistent state. Without such coordination, one side could commit while the other fails, causing account balances to diverge and require manual reconciliation.
- ✗
Schema flexibility
Why it's wrong here
Schema flexibility is the ability of a data store to accept records with different fields or evolve its structure without rigid constraints—common in document databases like Cosmos DB or MongoDB. This is helpful for storing account balances with varying metadata, but it is unrelated to transactional behavior. The problem of keeping a debit and credit consistent across stores is about write atomicity, not about how the data is shaped or migrated.
When this WOULD be correct
Schema flexibility would be the correct answer in a question asking about the advantage of using a NoSQL database like Cosmos DB over a relational database when dealing with rapidly changing data structures, such as in a content management system where each document can have different fields.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The DP-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓Distributed transaction coordinationCorrect answer▾
Why this is correct
A financial transfer that debits one account and credits another touches two independent storage systems. Distributed transaction coordination—via a two-phase commit or a saga pattern with compensating actions—ensures atomicity across those stores, so a failure in one step does not leave a partial, inconsistent state. Without such coordination, one side could commit while the other fails, causing account balances to diverge and require manual reconciliation.
✗ACID complianceWrong answer — click to see why▾
Why this is wrong here
ACID compliance applies to a single database system (like Azure SQL) ensuring atomicity, consistency, isolation, durability. The question involves coordinating two different databases (SQL and Cosmos DB) with different consistency models, which is beyond ACID's scope.
★ When this WOULD be the correct answer
A question asking about the property that ensures a database transaction is all-or-nothing, such as 'Which property guarantees that a transaction in a relational database either fully completes or fully rolls back?'
Why candidates choose this
Candidates see 'transaction rolled back' and 'consistency' and incorrectly associate ACID with the cross-database coordination, not realizing ACID is limited to a single database system.
✗IdempotencyWrong answer — click to see why▾
Why this is wrong here
Idempotency ensures that repeated operations produce the same result, but the difficulty here is coordinating atomic rollback across two different databases (SQL and Cosmos DB), not ensuring idempotent retries.
★ When this WOULD be the correct answer
A question describing a system where a payment processing API must safely handle duplicate requests (e.g., due to network retries) without causing double charges. The correct answer would be idempotency, as the API should produce the same result regardless of how many times the request is sent.
Why candidates choose this
Candidates may confuse idempotency with consistency guarantees, thinking that ensuring operations can be safely retried is the same as maintaining cross-database atomicity.
✗Schema flexibilityWrong answer — click to see why▾
Why this is wrong here
Schema flexibility refers to the ability to store data without a fixed schema, which is irrelevant to the challenge of ensuring atomicity across two different databases (Azure SQL and Cosmos DB) with different consistency models.
★ When this WOULD be the correct answer
Schema flexibility would be the correct answer in a question asking about the advantage of using a NoSQL database like Cosmos DB over a relational database when dealing with rapidly changing data structures, such as in a content management system where each document can have different fields.
Why candidates choose this
Candidates might confuse the need for data consistency across databases with the flexibility of data models, or they may incorrectly associate Cosmos DB's schema-agnostic nature with solving consistency problems.
Analysis generated from the official DP-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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 Cosmos DB
Azure Cosmos DB is a fully managed, globally distributed NoSQL database service that offers fast reads and writes anywhere in the world with automatic scaling and multiple consistency models.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DP-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DP-900 exam.