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raft: forget the leader when stepping down if it's safe #134990

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raft: forget the leader when stepping down if it's safe #134990

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Commits on Nov 22, 2024

  1. raft: start bcasting defortification messages when stepping down 

    Right now, we start bcasting defortificaton messages at heartbeat
timeouts. However, there is nothing that prevents us from starting this
process even earlier. This commit starts this process when stepping down
immediately after becoming a follower.

Epic: None

Release notes: None
    @iskettaneh
    iskettaneh committed Nov 22, 2024
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  2. raft: allow forgetting the leader within the same term 

    This commit allows us to forget the leader when stepping down. We can't
just call `r.resetLead()` inside `r.reset()` because it would defortify
in all places where we stepdown to the same term. Once we make it safe
in all places to stepdown to the same term and forget the leader, we
can call r.resetLead() inside r.reset().

Epic: None

Release note: None
    @iskettaneh
    iskettaneh committed Nov 22, 2024
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  3. raft: forget the leader when stepping down from CheckQuorum 

    In checkQuorum, if we decide to step down, it means that a majority
of replicas don't support us. Therefore, it's safe to step down and
forget that we were the leader at this term. We can safely campaign
and participate in elections.

Epic: None

Release note: None
    @iskettaneh
    iskettaneh committed Nov 22, 2024
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  4. raft: forget the leader when transferring leadership 

    Since leadership transfer means that the current leader instructs
another replica to campaign without performing safety checks. It
should be safe to forget the leader when stepping down.

Epic: None

Release note: None
    @iskettaneh
    iskettaneh committed Nov 22, 2024
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  5. raft: forget the leader when a leader becomes a learner 

    When a current leader becomes a learner, it should be safe to step down
and forget that we were the leader at the current term because:
(1) learners can't campaign or participate in elections, and (2) in
order for a learner to become a voter again, a new leader needs to get
elected and propose that change, which means that the replica would be
able to safely participate in elections then.

Epic: None

Release note: None
    @iskettaneh
    iskettaneh committed Nov 22, 2024
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  6. raft: forget the leader after a restart if we were the leader 

    This commit makes us forget that we were the leader at this term after
a restart.

Epic: None

Release notes: None
    @iskettaneh
    iskettaneh committed Nov 22, 2024
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  7. raft: forget the leader when stepping down after a VoteLost 

    We already forget the leader when attempting to campaign. This commit
doesn't change any current behaviour.

Epic: None

Release notes: None
    @iskettaneh
    iskettaneh committed Nov 22, 2024
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