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Spurious split-vote detected when a candidate wins with exactly a quorum of votes #8698

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sergepetrenko opened this issue May 24, 2023 · 0 comments · Fixed by #8699
Closed

Spurious split-vote detected when a candidate wins with exactly a quorum of votes #8698

sergepetrenko opened this issue May 24, 2023 · 0 comments · Fixed by #8699
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@sergepetrenko
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2.10 Target is 2.10 and all newer release/master branches bug Something isn't working raft RAFT protocol

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@sergepetrenko
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Bug description

Tarantool version: master (3.0.0-entrypoint-259-g13159230c).

A node configured as "candidate" spuriously detects a split-vote when another candidate should win elections with exactly a quorum of votes for self.

Steps to reproduce: 
--
-- Instance 1.
--

-- Step 1.
box.cfg{listen = 3301, replication = {3301, 3302}, election_mode = 'candidate'}

-- Step 3.
box.schema.user.grant('guest', 'replication')

--
-- Instance 2.
--

-- Step 2.
box.cfg{listen = 3302, replication = {3301, 3302}, election_mode = 'voter'}

-- Step 4.
box.cfg{election_mode = 'candidate'}
box.ctl.promote()

After the 4 steps you will be surprised that the instance 1 logs contain the message split vote is discovered:

2023-05-24 16:38:29.354 [20337] main/110/applier/3301 I> RAFT: message {term: 3, vote: 2, state: candidate, vclock: {1: 3}} from 2
2023-05-24 16:38:29.354 [20337] main/110/applier/3301 I> RAFT: received a newer term from 2
2023-05-24 16:38:29.354 [20337] main/110/applier/3301 I> RAFT: bump term to 3, follow
2023-05-24 16:38:29.354 [20337] main/110/applier/3301 I> RAFT: vote for 2, follow
2023-05-24 16:38:29.354 [20337] main/115/raft_worker I> RAFT: persisted state {term: 3}
2023-05-24 16:38:29.354 [20337] main/115/raft_worker I> RAFT: persisted state {term: 3, vote: 2}
2023-05-24 16:38:29.354 [20337] main/115/raft_worker I> RAFT: split vote is discovered - {1: 1, 2: 1}, new term in 0.097000 sec
@sergepetrenko sergepetrenko added bug Something isn't working raft RAFT protocol labels May 24, 2023
@sergepetrenko sergepetrenko self-assigned this May 24, 2023
sergepetrenko added a commit to sergepetrenko/tarantool that referenced this issue May 24, 2023
@sergepetrenko
raft: fix spurious split-vote
e62a64b 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes tarantool#8698

NO_DOC=bugfix
@sergepetrenko sergepetrenko mentioned this issue May 24, 2023
Merged
sergepetrenko added a commit to sergepetrenko/tarantool that referenced this issue May 24, 2023
@sergepetrenko
raft: fix spurious split-vote
7d85b33 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes tarantool#8698

NO_DOC=bugfix
@sergepetrenko sergepetrenko added the 2.10 Target is 2.10 and all newer release/master branches label May 24, 2023
sergepetrenko added a commit to sergepetrenko/tarantool that referenced this issue May 25, 2023
@sergepetrenko
raft: fix spurious split-vote
bef4007 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes tarantool#8698

NO_DOC=bugfix
sergepetrenko added a commit to sergepetrenko/tarantool that referenced this issue May 26, 2023
@sergepetrenko
raft: fix spurious split-vote
9e3521c 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes tarantool#8698

NO_DOC=bugfix
sergepetrenko added a commit to sergepetrenko/tarantool that referenced this issue May 29, 2023
@sergepetrenko
raft: fix spurious split-vote
1ec1f55 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes tarantool#8698

NO_DOC=bugfix
sergepetrenko added a commit that referenced this issue May 29, 2023
@sergepetrenko
raft: fix spurious split-vote
2afde5b 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes #8698

NO_DOC=bugfix
sergepetrenko added a commit that referenced this issue May 29, 2023
@sergepetrenko
raft: fix spurious split-vote
f796936 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes #8698

NO_DOC=bugfix

(cherry picked from commit 2afde5b)
sergepetrenko added a commit that referenced this issue May 29, 2023
@sergepetrenko
raft: fix spurious split-vote
3e0229f 
Due to a typo raft candidate counted a vote for another node as a vote
for self in its split-vote detector. This could lead to spurious
split-vote detection in cases when another node wins elections with a bare
minimum of votes for it (exactly a quorum of votes).

Closes #8698

NO_DOC=bugfix

(cherry picked from commit 2afde5b)
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Improve election stability and reproducibility sergepetrenko/tarantool
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