DBS-C01 Monitoring and Troubleshooting Practice Question
A retail company uses Amazon RDS for PostgreSQL as the backend for its e-commerce platform. During a flash sale, the database experienced high CPU utilization and increased the number of active connections. The application team reported that some queries timed out. The database specialist reviewed the slow query log and found that several queries were performing sequential scans on large tables due to missing indexes. The specialist created the necessary indexes, but the issue persists for some queries. Upon further investigation, the specialist notices that the query planner is still choosing sequential scans for some queries. What should the database specialist do to ensure the query planner uses the indexes?
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
✓
Run the ANALYZE command to update table statistics.
Running ANALYZE updates the table statistics used by the query planner, allowing it to make informed decisions about index usage. Without updated statistics, the planner may still choose sequential scans even after indexes are created. Option A is incorrect because increasing maintenance_work_mem speeds up index creation but does not affect query planning. Option B is incorrect because decreasing random_page_cost might make indexes more attractive, but it is a global setting that could have unintended consequences and does not address the root cause of stale statistics. Option D is incorrect because disabling sequential scans (enable_seqscan=off) forces index usage but can lead to suboptimal plans, especially if the index is not the most efficient access method.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase maintenance_work_mem to speed up index creation.
Why it's wrong here
This does not affect query planning.
- ✗
Decrease the random_page_cost to make indexes more attractive.
Why it's wrong here
This could help but is a tuning parameter; ANALYZE is the first step.
- ✓
Run the ANALYZE command to update table statistics.
Why this is correct
Updated statistics help the planner use indexes.
- ✗
Set enable_seqscan to off to force index usage.
Why it's wrong here
This may lead to suboptimal plans if indexes are not efficient.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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