Answer
An index-only scan satisfies a query using only index data when all required columns are in the index, avoiding table reads.
Quick Answer
Index-only scan reads all needed columns directly from the index without accessing the heap (table). Possible when: all SELECT columns are in the index, and the visibility map shows the page as all-visible (so PostgreSQL doesn't need to check heap for tuple visibility). Much faster than regular index scan (no heap fetch). Create covering indexes: include all frequently queried columns.
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