open-consul/vendor/github.com/hashicorp/raft/commitment.go

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package raft
import (
"sort"
"sync"
)
// Commitment is used to advance the leader's commit index. The leader and
// replication goroutines report in newly written entries with Match(), and
// this notifies on commitCh when the commit index has advanced.
type commitment struct {
// protectes matchIndexes and commitIndex
sync.Mutex
// notified when commitIndex increases
commitCh chan struct{}
// voter ID to log index: the server stores up through this log entry
matchIndexes map[ServerID]uint64
// a quorum stores up through this log entry. monotonically increases.
commitIndex uint64
// the first index of this leader's term: this needs to be replicated to a
// majority of the cluster before this leader may mark anything committed
// (per Raft's commitment rule)
startIndex uint64
}
// 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).
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,
}
}
// Called when a new cluster membership configuration is created: it will be
// used to determine commitment from now on. 'configuration' is the servers in
// the cluster.
func (c *commitment) setConfiguration(configuration Configuration) {
c.Lock()
defer c.Unlock()
oldMatchIndexes := c.matchIndexes
c.matchIndexes = make(map[ServerID]uint64)
for _, server := range configuration.Servers {
if server.Suffrage == Voter {
c.matchIndexes[server.ID] = oldMatchIndexes[server.ID] // defaults to 0
}
}
c.recalculate()
}
// Called by leader after commitCh is notified
func (c *commitment) getCommitIndex() uint64 {
c.Lock()
defer c.Unlock()
return c.commitIndex
}
// Match is called once a server completes writing entries to disk: either the
// leader has written the new entry or a follower has replied to an
// AppendEntries RPC. The given server's disk agrees with this server's log up
// through the given index.
func (c *commitment) match(server ServerID, matchIndex uint64) {
c.Lock()
defer c.Unlock()
if prev, hasVote := c.matchIndexes[server]; hasVote && matchIndex > prev {
c.matchIndexes[server] = matchIndex
c.recalculate()
}
}
// Internal helper to calculate new commitIndex from matchIndexes.
// Must be called with lock held.
func (c *commitment) recalculate() {
if len(c.matchIndexes) == 0 {
return
}
matched := make([]uint64, 0, len(c.matchIndexes))
for _, idx := range c.matchIndexes {
matched = append(matched, idx)
}
sort.Sort(uint64Slice(matched))
quorumMatchIndex := matched[(len(matched)-1)/2]
if quorumMatchIndex > c.commitIndex && quorumMatchIndex >= c.startIndex {
c.commitIndex = quorumMatchIndex
asyncNotifyCh(c.commitCh)
}
}