Databases · Middle · Question 6 of 75

What is a covering index and an index-only scan?

✓Correct answer: If the index contains all columns the query needs (e.g. via INCLUDE), PostgreSQL can answer from the index without reading the table
2A scan that reads only the first page of an index
3An index that covers every table in the database

Explanation

Index-only scans also depend on the visibility map, so tables with many recent changes still need some heap reads. VACUUM keeps the map up to date.

Further reading

PostgreSQL: Index-only scans and covering indexes ↗

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