Function explain_order 

pub fn explain_order(
    lmpg: &Lmpg,
    req: &SearchRequest,
    snap: &QuerySnapshot,
    skip: usize,
    limit: usize,
) -> Result<Option<OrderExplain>, QueryError>

The order-first plan of the page skip..skip + limit of req, if one wins; it does not read the page.

Errors

Returns storage read errors from the planners’ counters.