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63.4. Included attributes in B-tree indexes

As of PostgreSQL 11.0 there is an optional INCLUDE clause, which allows to add non-key (included) attributes to index. Those included attributes allow more queries to benefit from index-only scans. We never use included attributes in ScanKeys for search. That allows us to include into B-tree any datatypes, even those which don't have suitable operator classes. Included columns only stored in regular tuples on leaf pages. All pivot tuples on non-leaf pages and highkey tuples are truncated to contain only key attributes. That helps to slightly reduce the size of index.

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