[Raft] Add prevote to make it better #3322
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critical27
requested review from
darionyaphet,
cangfengzhs,
liwenhui-soul,
liuyu85cn,
panda-sheep,
SuperYoko and
pengweisong
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please fix the conflict thanks ~ |
liuyu85cn
reviewed
Nov 19, 2021
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| // The method returns the partition's role after the election | ||
| Role processElectionResponses(const ElectionResponses& results, | ||
| // Return true if I have been granted majority votes on proposedTerm, no matter isPreVote or not |
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comments of this method is exact the same as the above one...
liuyu85cn
approved these changes
Nov 19, 2021
| if (needToStartElection()) { | ||
| if (leaderElection().get()) { | ||
| VLOG(2) << idStr_ << "Stop the election"; | ||
| if (leaderElection(true).get() && leaderElection(false).get()) { |
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call leaderElection twice in a row 👍
darionyaphet
approved these changes
Nov 19, 2021
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Wait @kikimo to do a final test. |
kikimo
approved these changes
Nov 25, 2021
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Reference
See $9.6 in https://web.stanford.edu/~ouster/cgi-bin/papers/OngaroPhD.pdf, my implementation is almost same in https://www.openlife.cc/sites/default/files/4-modifications-for-Raft-consensus.pdf
Change notes:
current_term + 1to start a prevote, if I get majority votes, then start a formal election with++current_term(which is the same term in prevote). I believe most of the election logic is same as paper after this PR. Many scenario when we failed to get a leader will be eliminated.wal_->rollbackToLog(lastLogId_);is added, because if term changed during sending logs, thelastLogId_won't be updated. However, since we have write some logs into wal, if we don't rollback those logs, we can't write any logs anymore because the logId inconsistency in wal.Close #3108
@kikimo and I will do some test first, but ready to review.