Function explain_expansion 

pub fn explain_expansion<R: TryRead>(
    snap: &R,
    tenant: TenantId,
    labels: &[String],
    where_: &Expr,
) -> Result<Option<u64>, QueryError>

The traversal the planner answers by expanding backwards from its targets, for EXPLAIN and the unindexed-walk check: the estimated number of targets it starts from (the smallest, when several are expanded). None when no traversal conjunct is expanded.

Errors

Propagates storage reads from the estimates.