PostgreSQL - Performance Tuning
A query uses an index scan but runs very slowly. Which of these could be a cause?
A query uses an index scan but runs very slowly. Which of these could be a cause?
medium📝 Debug Q7 of 15
Step-by-Step Solution
Solution:
Step 1: Analyze index scan performance factors
If the indexed column has many duplicates, the index scan may fetch many rows, slowing the query.Step 2: Evaluate other options
Empty tables run fast; queries without WHERE usually use sequential scan; PostgreSQL supports index scans on large tables.Final Answer:
The index is on a column with many duplicate values, causing many row lookups. -> Option BQuick Check:
Slow index scan cause = B [OK]
Quick Trick: High duplicates in indexed column slow index scans [OK]
Common Mistakes:
- Thinking empty tables cause slow queries
- Assuming no WHERE means index scan
- Believing PostgreSQL limits index scans by table size
Master "Performance Tuning" in PostgreSQL
Want More Practice?
15+ quiz questions · All difficulty levels · Free
Free Signup - Practice All QuestionsMore PostgreSQL Quizzes