Question 330 of 997

Develop for Azure storage →mediumMultiple ChoiceObjective-mapped

AZ-204 Develop for Azure storage Practice Question

This AZ-204 practice question tests your understanding of develop for azure storage. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

You are developing an IoT solution that stores device metadata (device ID, location, firmware version, last seen timestamp) in Azure Table Storage. Each device has a unique DeviceId and a Timestamp. You need to design the PartitionKey and RowKey to optimize query performance for the following query: Retrieve all firmware versions for devices in a specific city that were last seen within the last 24 hours. The query must be efficient (partition scan minimized). Which key design is most appropriate?

Question 1mediummultiple choice

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A
PartitionKey = City, RowKey = DeviceId_Timestamp (e.g., "device123_2023-10-01T12:00:00")
Why wrong: This design allows querying by city but the row key is not sortable by timestamp, so you cannot do a range query on timestamp efficiently. You would have to scan all devices in the city and filter in the client.
B
PartitionKey = City, RowKey = Inverted timestamp (e.g., DateTime.MaxValue.Ticks - Timestamp.Ticks)
This design keeps all devices from the same city in one partition (efficient for city filtering). The row key, when sorted in ascending order, brings the most recent timestamps first. You can use a range query on the row key to get devices with last seen within the last 24 hours by comparing against the inverted timestamp of 24 hours ago.
C
PartitionKey = DeviceId, RowKey = Timestamp
Why wrong: Partitioning by DeviceId scatters data across partitions, meaning a query for devices in a specific city would require a full table scan (all partitions) to find matching cities, which is inefficient.
D
PartitionKey = City, RowKey = DeviceId
Why wrong: This allows efficient partition query by city, but the row key is device ID. To filter by timestamp, you would need to scan all rows in the partition and apply a filter, which is not efficient if the partition has many devices.

Full breakdown with real-world context →

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

✓

PartitionKey = City, RowKey = Inverted timestamp (e.g., DateTime.MaxValue.Ticks - Timestamp.Ticks)

Option B is correct because it uses City as the PartitionKey, ensuring all devices in the same city are in a single partition, and an inverted timestamp as the RowKey, which allows efficient range queries for the last 24 hours. Azure Table Storage sorts entities by RowKey within a partition, so querying for RowKey values greater than the inverted timestamp for 24 hours ago retrieves only the relevant rows without scanning the entire partition.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
PartitionKey = City, RowKey = DeviceId_Timestamp (e.g., "device123_2023-10-01T12:00:00")
Why it's wrong here
This design allows querying by city but the row key is not sortable by timestamp, so you cannot do a range query on timestamp efficiently. You would have to scan all devices in the city and filter in the client.
✓
PartitionKey = City, RowKey = Inverted timestamp (e.g., DateTime.MaxValue.Ticks - Timestamp.Ticks)
Why this is correct
This design keeps all devices from the same city in one partition (efficient for city filtering). The row key, when sorted in ascending order, brings the most recent timestamps first. You can use a range query on the row key to get devices with last seen within the last 24 hours by comparing against the inverted timestamp of 24 hours ago.
Related concept
Read the scenario before looking for a memorised answer.
✗
PartitionKey = DeviceId, RowKey = Timestamp
Why it's wrong here
Partitioning by DeviceId scatters data across partitions, meaning a query for devices in a specific city would require a full table scan (all partitions) to find matching cities, which is inefficient.
✗
PartitionKey = City, RowKey = DeviceId
Why it's wrong here
This allows efficient partition query by city, but the row key is device ID. To filter by timestamp, you would need to scan all rows in the partition and apply a filter, which is not efficient if the partition has many devices.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often choose Option D (PartitionKey = City, RowKey = DeviceId) because it groups by city, but they overlook that the timestamp filter would still require a full partition scan, failing the 'minimized partition scan' requirement.

Detailed technical explanation

How to think about this question

Azure Table Storage uses a sorted index on PartitionKey + RowKey, and queries with a range on RowKey (e.g., using greater-than or less-than operators) are highly efficient because they leverage the index without a full scan. The inverted timestamp trick (DateTime.MaxValue.Ticks - Timestamp.Ticks) ensures that more recent timestamps have higher RowKey values, making it easy to query for 'last 24 hours' by specifying a lower bound. This pattern is commonly used for time-series data where you need to retrieve the latest records quickly.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this AZ-204 question test?

Develop for Azure storage — This question tests Develop for Azure storage — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: PartitionKey = City, RowKey = Inverted timestamp (e.g., DateTime.MaxValue.Ticks - Timestamp.Ticks) — Option B is correct because it uses City as the PartitionKey, ensuring all devices in the same city are in a single partition, and an inverted timestamp as the RowKey, which allows efficient range queries for the last 24 hours. Azure Table Storage sorts entities by RowKey within a partition, so querying for RowKey values greater than the inverted timestamp for 24 hours ago retrieves only the relevant rows without scanning the entire partition.

What should I do if I get this AZ-204 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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