PostgreSQL - Performance Tuning
Why does PostgreSQL sometimes choose a sequential scan over an index scan even when an index exists?
Why does PostgreSQL sometimes choose a sequential scan over an index scan even when an index exists?
hard📝 Conceptual Q10 of 15
Step-by-Step Solution
Solution:
Step 1: Understand planner cost estimation
The planner estimates costs and chooses the fastest method based on row counts and data distribution.Step 2: Recognize when sequential scan is preferred
If many rows match, scanning the whole table can be faster than using an index.Final Answer:
Because the planner estimates that scanning the whole table is faster when many rows match -> Option BQuick Check:
Planner picks fastest plan based on row estimates [OK]
Quick Trick: Planner picks sequential scan if many rows match [OK]
Common Mistakes:
- Thinking indexes are only for sorting
- Believing PostgreSQL lacks index scan support
- Assuming sequential scans always use less memory
Master "Performance Tuning" in PostgreSQL
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