Method merge

nodedb-cluster/src/distributed_document/merge_sort.rs:59–70

Perform the global merge sort and apply the global LIMIT. Each shard already applied `ORDER BY + LIMIT` locally, so we have at most `num_shards × limit` rows. The global sort + limit produces the correct result.

(&mut self, global_limit: usize)

    /// at most `num_shards × limit` rows. The global sort + limit produces
    /// the correct result.
    pub fn merge(&mut self, global_limit: usize) -> Vec<ShardRow> {
        match self.direction {
            SortDirection::Ascending => {
                self.rows.sort_by(|a, b| a.sort_key.cmp(&b.sort_key));
            }
            SortDirection::Descending => {
                self.rows.sort_by(|a, b| b.sort_key.cmp(&a.sort_key));
            }
        }
        self.rows.truncate(global_limit);
        self.rows.clone()
    }

    /// Total rows collected before merge.
    pub fn total_rows(&self) -> usize {