COMPOSITE_TERM

A composite term over one array element: the values of several fields of the same element, keyed together.

The one kind that answers a correlated question. An ordinary conjunction over an array path is existential in each leaf independently, so and($.items[*].sku eq "A", $.items[*].qty eq 5) matches a document whose sku came from one element and qty from another — a defined semantics, and one that returned 5-6x the documents a caller wanting the correlated question keeps, measured over corpora whose element fields vary independently. This kind keys the tuple, so the correlated question is answered by a dictionary lookup.

Never recommended, only asked for. The same measurement found the rate is exactly zero on a corpus whose element fields move together, so a recommender would be spending bytes on a shape it cannot see from a sketch. IndexCandidates are never of this kind; it is created by name, with the fields named too.

It answers a fully known conjunction and nothing else — every declared field compared for equality, in one elemMatch — which is Postgres jsonb_path_ops's documented limit and the reason this supplements the leaf indexes rather than replacing them.