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