// Helper method to find potential new commitIndex.
// Returns the highest N possible that is higher than currentCommitIndex.
// Returns 0 if no match found.
// #RFS-L4: If there exists an N such that N > commitIndex, a majority
// of matchIndex[i] >= N, and log[N].term == currentTerm:
// set commitIndex = N (#5.3, #5.4)
func FindNewerCommitIndex(
ci *config.ClusterInfo,
lvs *LeaderVolatileState,
log LogReadOnly,
currentTerm TermNo,
currentCommitIndex LogIndex,
) (LogIndex, error) {
indexOfLastEntry, err := log.GetIndexOfLastEntry()
if err != nil {
return 0, err
}
requiredMatches := ci.QuorumSizeForCluster()
var matchingN LogIndex = 0
// cover all N > currentCommitIndex
// stop when we pass the end of the log
for N := currentCommitIndex + 1; N <= indexOfLastEntry; N++ {
// check log[N].term
termAtN, err := log.GetTermAtIndex(N)
if err != nil {
return 0, err
}
if termAtN > currentTerm {
// term has gone too high for log[N].term == currentTerm
// no point trying further
break
}
if termAtN < currentTerm {
continue
}
// finally, check for majority of matchIndex
var foundMatches uint = 1 // 1 because we already match!
for _, peerMatchIndex := range lvs.MatchIndex {
if peerMatchIndex >= N {
foundMatches++
}
}
if foundMatches >= requiredMatches {
matchingN = N
}
}
return matchingN, nil
}
// New instance set up for a fresh election
func NewCandidateVolatileState(
clusterInfo *config.ClusterInfo,
) (*CandidateVolatileState, error) {
cvs := &CandidateVolatileState{
1, // assumes we always vote for ourself
clusterInfo.QuorumSizeForCluster(),
make(map[ServerId]bool),
}
err := clusterInfo.ForEachPeer(
func(peerId ServerId) error {
cvs.VotedPeers[peerId] = false
return nil
},
)
if err != nil {
return nil, err
}
return cvs, nil
}