The correct answer is to perform an ALTER INDEX REORGANIZE with the COMPRESS_ALL_ROW_GROUPS option on the affected columnstore indexes. This command is the right choice because it compresses all row groups—including those in the delta store—and physically removes deleted rows that are consuming storage space due to fragmentation, all while remaining an online operation. On the Microsoft Azure Database Administrator Associate DP-300 exam, this scenario tests your understanding of columnstore index maintenance in Azure SQL Managed Instance, specifically how to reclaim storage space from columnstore index fragmentation without blocking queries during business hours. A common trap is choosing ALTER INDEX REBUILD, which is offline and resource-intensive, or assuming that simply dropping and recreating indexes is necessary. Remember the memory tip: “REORGANIZE with COMPRESS_ALL_ROW_GROUPS compresses and cleans online, while REBUILD is offline and mean.”
DP-300 Practice Question: Monitor, configure, and optimize database resources
This DP-300 practice question tests your understanding of monitor, configure, and optimize database resources. 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 the database administrator for an Azure SQL Managed Instance hosting a data warehouse workload. You notice that the storage space consumed by the database is significantly larger than expected. The database has multiple large tables with clustered columnstore indexes. You suspect that the columnstore indexes have become fragmented and that deleted rows are consuming space. You need to reclaim storage space with minimal impact on query performance during business hours. What should you do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Perform an ALTER INDEX REORGANIZE with the COMPRESS_ALL_ROW_GROUPS option on the affected columnstore indexes.
Option B is correct because REORGANIZE with COMPRESS_ALL_ROW_GROUPS compresses all row groups, including those in the delta store, and removes deleted rows from columnstore indexes. This operation is online and can be performed during business hours with minimal impact on query performance, unlike a rebuild which is offline and resource-intensive. It directly addresses the fragmentation and deleted row space consumption in columnstore indexes.
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.
✗
Perform an ALTER INDEX REBUILD on the affected columnstore indexes after business hours.
Why it's wrong here
REBUILD is an offline operation that locks the table, impacting availability.
✓
Perform an ALTER INDEX REORGANIZE with the COMPRESS_ALL_ROW_GROUPS option on the affected columnstore indexes.
Why this is correct
This online operation reorganizes and compresses all row groups, reclaiming space from deleted rows with minimal impact.
Related concept
Read the scenario before looking for a memorised answer.
✗
Perform an ALTER INDEX REORGANIZE on the affected columnstore indexes.
Why it's wrong here
REORGANIZE alone does not compress delta row groups and may not fully reclaim space from deleted rows.
✗
Rebuild the entire database by creating a new database and copying data.
Why it's wrong here
This is excessive and causes significant downtime.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume any REORGANIZE is sufficient, but without COMPRESS_ALL_ROW_GROUPS, it does not address deleted rows or delta store row groups, so the space is not reclaimed.
Detailed technical explanation
How to think about this question
In columnstore indexes, deleted rows are tracked in a delete bitmap and are not physically removed until a rebuild or a reorganize with COMPRESS_ALL_ROW_GROUPS is performed. The COMPRESS_ALL_ROW_GROUPS option forces all open delta store row groups to be compressed into compressed row groups, and during this process, deleted rows are eliminated. This operation is fully online and uses minimal locks, making it suitable for production workloads during business hours.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-300 question in full detail.
Monitor, configure, and optimize database resources — This question tests Monitor, configure, and optimize database resources — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Perform an ALTER INDEX REORGANIZE with the COMPRESS_ALL_ROW_GROUPS option on the affected columnstore indexes. — Option B is correct because REORGANIZE with COMPRESS_ALL_ROW_GROUPS compresses all row groups, including those in the delta store, and removes deleted rows from columnstore indexes. This operation is online and can be performed during business hours with minimal impact on query performance, unlike a rebuild which is offline and resource-intensive. It directly addresses the fragmentation and deleted row space consumption in columnstore indexes.
What should I do if I get this DP-300 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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Question Discussion
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