Method evict_from_highest_overshoot

nodedb/src/engine/sparse/doc_cache.rs:350–374

Evict one entry from the shard with the highest overshoot ratio. Among shards with equal overshoot ratios, `hint_db_id` (the inserting shard) is preferred so that a cold shard at its proportional share is never displaced in favour of the hot inserting shard. Returns `false` if all shards are empty.

(&mut self, hint_db_id: u64)

    ///
    /// Returns `false` if all shards are empty.
    fn evict_from_highest_overshoot(&mut self, hint_db_id: u64) -> bool {
        let total_weight = self.total_weight();
        let db_id = self
            .shards
            .iter()
            .filter(|(_, s)| !s.entries.is_empty())
            .max_by_key(|(id, s)| {
                let score = s.overshoot_score(total_weight);
                // Prefer the inserting shard on ties so equal-ratio cold shards
                // are not evicted in its place.
                let is_hint = u8::from(**id == hint_db_id);
                (score, is_hint)
            })
            .map(|(&id, _)| id);
        match db_id {
            Some(id) => {
                let removed = self.shards.get_mut(&id).expect("just found").evict_one();
                if removed {
                    self.total = self.total.saturating_sub(1);
                }
                removed
            }
            None => false,
        }
    }
}

#[cfg(test)]