raft: enter candidate state immediately when starting a singleton clu…

…ster When a node starts it does not immediately becomes a candidate since it waits to learn about already existing leader and randomize the time it becomes a candidate to prevent dueling candidates if several nodes are started simultaneously. If a cluster consist of only one node there is no point in waiting before becoming a candidate though because two cases above cannot happen. This patch checks that the node belongs to a singleton cluster where the node itself is the only voting member and becomes candidate immediately. This reduces the starting time of a single node cluster which are often used in testing. Message-Id: <[email protected]>
sarvex · Mar 4, 2022 · 108e7fc · 108e7fc
1 parent 1c5ab5d
commit 108e7fc
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Showing 3 changed files with 5 additions and 6 deletions.
diff --git a/raft/fsm.cc b/raft/fsm.cc
@@ -33,7 +33,11 @@ fsm::fsm(server_id id, term_t current_term, server_id voted_for, log log,
     logger.trace("fsm[{}]: starting, current term {}, log length {}, commit index {}", _my_id, _current_term, _log.last_idx(), _commit_idx);
 
     // Init timeout settings
-    reset_election_timeout();
+    if (_log.get_configuration().current.size() == 1 && _log.get_configuration().can_vote(_my_id)) {
+        become_candidate(_config.enable_prevoting);
+    } else {
+        reset_election_timeout();
+    }
 }
 
 fsm::fsm(server_id id, term_t current_term, server_id voted_for, log log,

diff --git a/test/raft/etcd_test.cc b/test/raft/etcd_test.cc
@@ -487,7 +487,6 @@ BOOST_AUTO_TEST_CASE(test_single_node_commit) {
     raft::log log{raft::snapshot_descriptor{.config = cfg}};
     raft::fsm fsm(id1, term_t{}, server_id{}, std::move(log), trivial_failure_detector, fsm_cfg);
 
-    make_candidate(fsm);
     BOOST_CHECK(fsm.is_leader());  // Single node skips candidate state
     output = fsm.get_output();
     BOOST_CHECK(output.log_entries.size() == 1);
@@ -670,7 +669,6 @@ BOOST_AUTO_TEST_CASE(test_single_node_pre_candidate) {
     raft::log log1{raft::snapshot_descriptor{.config = cfg}};
     raft::fsm fsm1(id1, term_t{}, server_id{}, std::move(log1), trivial_failure_detector, fsm_cfg_pre);
 
-    make_candidate(fsm1);
     BOOST_CHECK(fsm1.is_leader());
 }
 

diff --git a/test/raft/fsm_test.cc b/test/raft/fsm_test.cc
@@ -303,8 +303,6 @@ void test_election_single_node_helper(raft::fsm_config fcfg) {
     raft::log log{raft::snapshot_descriptor{.config = cfg}};
     raft::fsm fsm(id1, term_t{}, server_id{}, std::move(log), trivial_failure_detector, fcfg);
 
-    BOOST_CHECK(fsm.is_follower());
-
     election_timeout(fsm);
 
     // Immediately converts from leader to follower if quorum=1
@@ -1150,7 +1148,6 @@ BOOST_AUTO_TEST_CASE(test_confchange_a_to_b) {
     log.emplace_back(make_lw_shared<raft::log_entry>(B.add_entry(raft::configuration({A_id}))));
     log.stable_to(log.last_idx());
     raft::fsm B_1(B_id, B.get_current_term(), B_id, std::move(log), trivial_failure_detector, fsm_cfg);
-    BOOST_CHECK(B_1.is_follower());
     election_timeout(B_1);
     communicate(A, B_1);
     BOOST_CHECK(B_1.is_follower());