If MsgTimeoutNow arrived after a node was removed, the node could start
and win an election, then panic in becomeLeader (see
cockroachdb/cockroach#8535)
Move all vote handling from the per-state step functions to the
top-level Step(). This wasn't necessary before because MsgVote would
cause us to become a follower, but MsgPreVote needs to be handled
without changing the node's current state.
Some tests were starting nodes with a non-empty log but a term of zero,
which cannot happen in the real world. This was affecting the final term
being tested in TestLeaderElection.
TickQuiesced allows the caller to support "quiesced" Raft groups which
do not perform periodic heartbeats and elections. This is useful in a
system with thousands of Raft groups where these periodic operations can
be overwhelming in an otherwise idle system.
It might seem possible to avoid advancing the logical clock at all in
such Raft groups, but doing so has an interaction with the CheckQuorum
functionality. If a follower is not quiesced while the leader is the
follower can call an election that will fail because the leader's lease
has not expired (electionElapsed < electionTimeout). The next time the
leader sends a heartbeat to this follower the follower will see that the
heartbeat is from a previous term and respond with a MsgAppResp. This in
turn will cause the leader to step down and become a follower even
though there isn't a leader in the group. By allowing the leader's
logical clock to advance via TickQuiesced, the leader won't reject the
election and there will be a smooth transfer of leadership to the
follower.
Grow the inflights buffer as needed instead of preallocating it to its
max size. This avoids preallocating a lot of unnecessary
space (8*MaxInflightMsgs) when using lots of raft groups while still
allowing for a reasonable MaxInflightMsgs configuration.
rand.NewSource creates a 4872 byte object. With a small number of raft
groups in a process this isn't a problem. With 10k raft groups we'd use
46MB for these random sources. The only usage is in
raft.resetRandomizedElectionTimeout which isn't performance critical.
Fixes#6347.
Previously, the checkQuorum flag required an election timeout to
expire before a node could cast its first vote. This change permits
the node to cast a vote at any time when the leader is not known,
including immediately after startup.
