Method try_advance_commit_index

nodedb-raft/src/node/internal.rs:323–353

Try to advance `commit_index` based on the voter quorum only. Learners' `match_index` is tracked (so we know when they are caught up for promotion) but intentionally excluded from this calculation so adding a learner never weakens the commit quorum.

(&mut self)

    /// up for promotion) but intentionally excluded from this calculation
    /// so adding a learner never weakens the commit quorum.
    pub(super) fn try_advance_commit_index(&mut self) {
        let leader = match &self.leader_state {
            Some(ls) => ls,
            None => return,
        };

        let last = self.log.last_index();
        for n in (self.volatile.commit_index + 1..=last).rev() {
            let term_at_n = match self.log.term_at(n) {
                Some(t) => t,
                None => continue,
            };

            if term_at_n != self.hard_state.current_term {
                continue;
            }

            let mut count = 1u64; // self counts.
            for &peer in &self.config.peers {
                if leader.match_index_for(peer) >= n {
                    count += 1;
                }
            }

            if count as usize >= self.config.quorum() {
                self.volatile.commit_index = n;
                self.collect_committed_entries();
                break;
            }
        }
    }

    pub(super) fn collect_committed_entries(&mut self) {
        let from = self.volatile.last_applied + 1;