<sect1 id="btree-included-attributes">

<title>Included attributes in B-tree indexes</title>

<para>

As of <productname>PostgreSQL</productname> 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.

</para>

</sect1>