Answer
The visibility map tracks pages containing only visible tuples, enabling index-only scans without reading table pages.
Quick Answer
The visibility map is a per-table file with one bit per page tracking if all tuples on that page are visible to all transactions. Index-only scans use the visibility map to avoid fetching the heap page to verify tuple visibility. VACUUM updates the visibility map. Pages with all-visible tuples allow index-only scans, dramatically improving read performance for covering indexes.
S
SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ