Given a table employees with an index on department_id, what will the Bitmap Index Scan do when you run:
medium📝 query result Q13 of 15
PostgreSQL - Performance Tuning
Given a table employees with an index on department_id, what will the Bitmap Index Scan do when you run: EXPLAIN SELECT * FROM employees WHERE department_id = 5;?
AIt creates a bitmap of row locations where department_id = 5, then fetches those rows efficiently
BIt scans the entire table sequentially without using the index
CIt updates the rows where department_id = 5
DIt deletes rows where department_id = 5
Step-by-Step Solution
Solution:
Step 1: Understand Bitmap Index Scan on condition
The scan uses the index on department_id to find matching rows and creates a bitmap of their locations.
Step 2: Explain how rows are fetched
Using the bitmap, it fetches only those rows efficiently from the table, avoiding full scan.
Final Answer:
It creates a bitmap of row locations where department_id = 5, then fetches those rows efficiently -> Option A
Quick Check:
Bitmap Index Scan finds matching rows then fetches [OK]
Quick Trick:Bitmap Index Scan finds and fetches matching rows efficiently [OK]
Common Mistakes:
Thinking it scans the whole table sequentially
Confusing scan with update or delete operations
Assuming it fetches rows without bitmap
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