Question: Reads from followers about nuraft

[greensky00]

Read-path is not a part of Raft protocol. You can use your own way to ask the leader for its committed index.

get_leader_committed_log_idx() returns the last "seen" committed index from heartbeats or append_entries messages from the leader. So it can be outdated at the time when a follower reads this value.

But please note that even though a follower directly asks the leader for the committed index, that value also can be outdated at the time when the follower receives the response from the leader. So there is no guarantee in either way.

[greensky00]

I see. For that purpose, you can use this API

NuRaft/include/libnuraft/raft_server.hxx

Lines 437 to 445 in c621949

	/**
	* Check if there is live leader in the current cluster.
	*
	* @return `true` if live leader exists.
	*/
	bool is_leader_alive() const {
	if ( leader_ == -1 || !hb_alive_ ) return false;
	return true;
	}

It returns false if a follower is partitioned from the leader.

[alesapin]

Thanks, I think stale reads are OK in my case. What is the best way to check that we are not completely partitioned from the leader (still receiving heartbeats)? https://github.com/eBay/NuRaft/blob/master/include/libnuraft/raft_server.hxx#L442-L444?

[alesapin]

Thanks!