Quick Answer
The answer is to run ALTER INDEX REORGANIZE with COMPRESS_ALL_ROW_GROUPS = ON. This command performs online columnstore index maintenance without blocking writes, as it incrementally compresses all open and closed rowgroups into fully compressed segments while the table remains accessible for concurrent transactions. On the Microsoft Azure Data Engineer Associate DP-203 exam, this scenario tests your understanding of the critical difference between REORGANIZE (online, non-blocking) and REBUILD (offline, blocking) for columnstore indexes in Azure Synapse dedicated SQL pools. A common trap is choosing REBUILD because it seems more thorough, but it locks the table and violates the requirement to avoid downtime. Remember the memory tip: “Reorganize is online and gentle; rebuild is offline and heavy.” For fixing columnstore index quality without blocking writes, always reach for REORGANIZE with the COMPRESS_ALL_ROW_GROUPS option.
This DP-203 practice question tests your understanding of secure, monitor, and optimize data storage and data processing. 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 manage an Azure Synapse Analytics dedicated SQL pool that contains a large fact table 'Orders' with 500 million rows. The table is hash-distributed on 'OrderDate' and uses a clustered columnstore index. Query performance has degraded over time. You check the system DMVs and find that the columnstore segments have poor quality, with many deleted rows and compressed rowgroups below 1 million rows. You need to improve query performance without blocking writes to the table. What should you do?
Run ALTER INDEX REORGANIZE with COMPRESS_ALL_ROW_GROUPS = ON.
Online operation that improves columnstore quality.
Drop and recreate the clustered columnstore index.
Why wrong: Offline and disrupts availability.
Re-cluster the table using a different distribution key.
Why wrong: Re-clustering changes distribution, not columnstore quality.
Run ALTER INDEX REBUILD on the clustered columnstore index.
Why wrong: REBUILD is an offline operation.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Run ALTER INDEX REORGANIZE with COMPRESS_ALL_ROW_GROUPS = ON.
Option B is correct because ALTER INDEX REORGANIZE with COMPRESS_ALL_ROW_GROUPS option rebuilds columnstore segments online without blocking. Option A is wrong because REBUILD is offline and blocks writes. Option C is wrong because dropping and recreating the index is offline. Option D is wrong because reclustering reorganizes data within a distribution but does not fix columnstore quality.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Run ALTER INDEX REORGANIZE with COMPRESS_ALL_ROW_GROUPS = ON.
Why this is correct
Online operation that improves columnstore quality.
Related concept
Read the scenario before looking for a memorised answer.
Drop and recreate the clustered columnstore index.
Why it's wrong here
Offline and disrupts availability.
Re-cluster the table using a different distribution key.
Why it's wrong here
Re-clustering changes distribution, not columnstore quality.
Run ALTER INDEX REBUILD on the clustered columnstore index.
Why it's wrong here
REBUILD is an offline operation.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Identify which DP-203 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Secure, monitor, and optimize data storage and data processing — This question tests Secure, monitor, and optimize data storage and data processing — Read the scenario before looking for a memorised answer..
The correct answer is: Run ALTER INDEX REORGANIZE with COMPRESS_ALL_ROW_GROUPS = ON. — Option B is correct because ALTER INDEX REORGANIZE with COMPRESS_ALL_ROW_GROUPS option rebuilds columnstore segments online without blocking. Option A is wrong because REBUILD is offline and blocks writes. Option C is wrong because dropping and recreating the index is offline. Option D is wrong because reclustering reorganizes data within a distribution but does not fix columnstore quality.
Identify which DP-203 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 21, 2026
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