Fix OnRequestVote RPC callback
Summary: RPC recipient should update its term even if it is rejecting the request. Reviewers: mislav.bradac, buda Reviewed By: mislav.bradac Subscribers: pullbot Differential Revision: https://phabricator.memgraph.io/D1039
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Marin Tomic
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4982d45e27
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6b4a2cafc5
@ -197,6 +197,9 @@ bool RaftMemberImpl<State>::SendRPC(const std::string &recipient,
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return false;
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}
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DCHECK(reply.Term() >= term_)
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<< "Response term should be >= request term";
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/* [Raft thesis, Section 3.3]
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* "Current terms are exchanged whenever servers communicate; if one server's
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* current term is smaller than the other's, then it updates its current term
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@ -424,6 +427,18 @@ PeerRPCReply::RequestVote RaftMemberImpl<State>::OnRequestVote(
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return reply;
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}
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/* [Raft thesis, Section 3.3]
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* "Current terms are exchanged whenever servers communicate; if one server's
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* current term is smaller than the other's, then it updates its current term
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* to the larger value. If a candidate or leader discovers that its term is
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* out of date, it immediately reverts to follower state." */
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if (request.candidate_term > term_) {
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if (mode_ != RaftMode::FOLLOWER) {
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CandidateOrLeaderTransitionToFollower();
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}
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UpdateTermAndVotedFor(request.candidate_term, {});
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}
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/* [Raft thesis, Section 3.6.1]
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* "Raft uses the voting process to prevent a candidate from winning an
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* election unless its log contains all committed entries. (...) The
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@ -457,18 +472,7 @@ PeerRPCReply::RequestVote RaftMemberImpl<State>::OnRequestVote(
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return reply;
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}
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/* [Raft thesis, Section 3.3]
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* "Current terms are exchanged whenever servers communicate; if one server's
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* current term is smaller than the other's, then it updates its current term
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* to the larger value. If a candidate or leader discovers that its term is
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* out of date, it immediately reverts to follower state." */
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if (request.candidate_term > term_) {
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if (mode_ != RaftMode::FOLLOWER) {
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CandidateOrLeaderTransitionToFollower();
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}
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}
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/* Now we now we will vote for this candidate, because it's term is at least
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/* Now we know we will vote for this candidate, because it's term is at least
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* as big as ours and we haven't voted for anyone else. */
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UpdateTermAndVotedFor(request.candidate_term, request.candidate_id);
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@ -344,12 +344,11 @@ TEST_P(OnRequestVoteTest, RequestVoteTest) {
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EXPECT_EQ(reply.vote_granted, GetParam().expected_reply);
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/* Our term should always be at least as large as sender's term. */
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/* If we accepted the request, our term should be equal to candidate's term
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* and voted_for should be set. */
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EXPECT_EQ(reply.term,
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reply.vote_granted ? GetParam().peer_term : GetParam().term);
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EXPECT_EQ(storage_.term_,
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reply.vote_granted ? GetParam().peer_term : GetParam().term);
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EXPECT_EQ(reply.term, std::max(GetParam().peer_term, GetParam().term));
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EXPECT_EQ(storage_.term_, std::max(GetParam().peer_term, GetParam().term));
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EXPECT_EQ(storage_.voted_for_,
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reply.vote_granted ? "b" : GetParam().voted_for);
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}
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@ -444,7 +443,6 @@ struct OnAppendEntriesTestParam {
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LogIndex peer_next_index;
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bool expected_reply;
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TermId expected_term;
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std::vector<LogEntry<DummyState>> expected_log;
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};
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@ -468,9 +466,10 @@ TEST_P(OnAppendEntriesTest, All) {
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{GetParam().peer_term, "b", last_log_index, last_log_term, entries, 0});
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EXPECT_EQ(reply.success, GetParam().expected_reply);
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EXPECT_EQ(reply.term, GetParam().expected_term);
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EXPECT_EQ(reply.term, std::max(GetParam().peer_term, GetParam().term));
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EXPECT_EQ(storage_.log_, GetParam().expected_log);
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}
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/* Member 'a' recieved AppendEntries RPC from member 'b'. The request will
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* contain no log entries, representing just a heartbeat, as it is not
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* important in these scenarios. */
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@ -484,7 +483,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {2}, {3}, {4}, {5}, {5}, {6}},
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7,
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false,
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8,
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{{1}, {1}, {2}}},
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/* we're missing entries 4, 5 and 6 -> decline, but update term */
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OnAppendEntriesTestParam{4,
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@ -493,7 +491,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {2}, {3}, {4}, {5}, {5}, {6}},
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7,
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false,
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8,
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{{1}, {1}, {2}}},
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/* we're missing entry 4 -> decline, but update term */
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OnAppendEntriesTestParam{5,
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@ -502,7 +499,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {2}, {3}, {4}, {5}, {5}, {6}},
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5,
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false,
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8,
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{{1}, {1}, {2}}},
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/* log terms don't match at entry 4 -> decline, but update term */
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OnAppendEntriesTestParam{5,
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@ -511,7 +507,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {3}, {3}, {4}, {5}, {5}, {6}},
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4,
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false,
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8,
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{{1}, {1}, {2}}},
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/* logs match -> accept and update term */
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OnAppendEntriesTestParam{5,
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@ -520,7 +515,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {2}, {3}, {4}, {5}, {5}, {6}},
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4,
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true,
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8,
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{{1}, {1}, {2}, {3}, {4}, {5}, {5}, {6}}},
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/* now follow some log truncation tests */
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/* no truncation, append a single entry */
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@ -531,7 +525,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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9,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}}},
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/* no truncation, append multiple entries */
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OnAppendEntriesTestParam{
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@ -541,7 +534,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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4,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}}},
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/* no truncation, leader's log is prefix of ours */
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OnAppendEntriesTestParam{
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@ -551,7 +543,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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4,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}, {6}}},
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/* another one, now with entries from newer term */
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OnAppendEntriesTestParam{
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@ -561,7 +552,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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4,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}, {7}, {7}}},
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/* no truncation, partial match between our log and appended entries
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*/
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@ -572,7 +562,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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4,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}}},
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/* truncate suffix */
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OnAppendEntriesTestParam{
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@ -582,7 +571,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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5,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}}},
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/* truncate suffix, with partial match between our log and appened
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entries */
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@ -593,7 +581,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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4,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}}},
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/* delete whole log */
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OnAppendEntriesTestParam{
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@ -603,7 +590,6 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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1,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}}},
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/* append on empty log */
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OnAppendEntriesTestParam{
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@ -613,5 +599,4 @@ INSTANTIATE_TEST_CASE_P(
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}},
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1,
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true,
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8,
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{{1}, {1}, {1}, {4}, {4}, {5}, {5}, {6}, {6}, {6}}}));
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