func newCommitment(commitCh chan struct{}, configuration Configuration, startIndex uint64) *commitment {
	matchIndexes := make(map[ServerID]uint64)
	for _, server := range configuration.Servers {
		if server.Suffrage == Voter {
			matchIndexes[server.ID] = 0
		}
	}
	return &commitment{
		commitCh:     commitCh,
		matchIndexes: matchIndexes,
		commitIndex:  0,
		startIndex:   startIndex,
	}
}
func newCommitment(commitCh chan struct{}, configuration Configuration, startIndex uint64) *commitment {
	matchIndexes := make(map[ServerID]uint64)
	for _, server := range configuration.Servers {
		if server.Suffrage == Voter {
			matchIndexes[server.ID] = 0
		}
	}
	return &commitment{
		commitCh:     commitCh,
		matchIndexes: matchIndexes,
		commitIndex:  0,
		startIndex:   startIndex,
	}
}
// newCommitment returns an commitment struct that notifies the provided
// channel when log entries have been committed. A new commitment struct is
// created each time this server becomes leader for a particular term.
// 'configuration' is the servers in the cluster.
// 'startIndex' is the first index created in this term (see
// its description above).