Covering Index
A covering index contains all columns a query needs, letting it be answered from the index alone without table lookups (index-only scan).
Purpose
To eliminate table-lookup I/O and speed up queries; an advanced index-optimization technique.
Mechanism
If every SELECT column is in the index (key columns + INCLUDE columns), the query reads only index pages, not data pages. PostgreSQL adds non-key columns via the INCLUDE clause. Reducing random I/O yields significant gains.
Use cases
- Query performance optimization
- Index design
- I/O reduction