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raftexample: implement Raft snapshot

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This commit is contained in:
Gyu-Ho Lee 2016-09-21 04:16:50 -07:00
parent 4b83f40618
commit e4fbf7db00
5 changed files with 117 additions and 40 deletions
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24
contrib/raftexample/httpapi.go
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@ -18,7 +18,6 @@ import (
"io/ioutil"
"log"
"net/http"
"os"
"strconv"
"github.com/coreos/etcd/raft/raftpb"
@ -102,25 +101,22 @@ func (h *httpKVAPI) ServeHTTP(w http.ResponseWriter, r *http.Request) {
}
// serveHttpKVAPI starts a key-value server with a GET/PUT API and listens.
func serveHttpKVAPI(port int, proposeC chan<- string, confChangeC chan<- raftpb.ConfChange,
commitC <-chan *string, errorC <-chan error) {
// exit when raft goes down
go func() {
if err, ok := <-errorC; ok {
log.Fatal(err)
}
os.Exit(0)
}()
func serveHttpKVAPI(kv *kvstore, port int, confChangeC chan<- raftpb.ConfChange, errorC <-chan error) {
srv := http.Server{
Addr: ":" + strconv.Itoa(port),
Handler: &httpKVAPI{
store: newKVStore(proposeC, commitC, errorC),
store: kv,
confChangeC: confChangeC,
},
}
if err := srv.ListenAndServe(); err != nil {
go func() {
if err := srv.ListenAndServe(); err != nil {
log.Fatal(err)
}
}()
// exit when raft goes down
if err, ok := <-errorC; ok {
log.Fatal(err)
}
}

26
contrib/raftexample/kvstore.go
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@ -20,13 +20,16 @@ import (
"encoding/json"
"log"
"sync"
"github.com/coreos/etcd/snap"
)
// a key-value store backed by raft
type kvstore struct {
proposeC chan<- string // channel for proposing updates
mu sync.RWMutex
kvStore map[string]string // current committed key-value pairs
proposeC chan<- string // channel for proposing updates
mu sync.RWMutex
kvStore map[string]string // current committed key-value pairs
snapshotter *snap.Snapshotter
}
type kv struct {
@ -34,8 +37,8 @@ type kv struct {
Val string
}
func newKVStore(proposeC chan<- string, commitC <-chan *string, errorC <-chan error) *kvstore {
s := &kvstore{proposeC: proposeC, kvStore: make(map[string]string)}
func newKVStore(snapshotter *snap.Snapshotter, proposeC chan<- string, commitC <-chan *string, errorC <-chan error) *kvstore {
s := &kvstore{proposeC: proposeC, kvStore: make(map[string]string), snapshotter: snapshotter}
// replay log into key-value map
s.readCommits(commitC, errorC)
// read commits from raft into kvStore map until error
@ -62,7 +65,18 @@ func (s *kvstore) readCommits(commitC <-chan *string, errorC <-chan error) {
for data := range commitC {
if data == nil {
// done replaying log; new data incoming
return
// OR signaled to load snapshot
snapshot, err := s.snapshotter.Load()
if err == snap.ErrNoSnapshot {
return
}
if err != nil && err != snap.ErrNoSnapshot {
log.Panic(err)
}
log.Printf("loading snapshot at term %d and index %d", snapshot.Metadata.Term, snapshot.Metadata.Index)
if err := s.recoverFromSnapshot(snapshot.Data); err != nil {
log.Panic(err)
}
}
var dataKv kv

8
contrib/raftexample/main.go
View File

@ -34,8 +34,12 @@ func main() {
defer close(confChangeC)
// raft provides a commit stream for the proposals from the http api
commitC, errorC := newRaftNode(*id, strings.Split(*cluster, ","), *join, proposeC, confChangeC)
var kvs *kvstore
getSnapshot := func() ([]byte, error) { return kvs.getSnapshot() }
commitC, errorC, snapshotterReady := newRaftNode(*id, strings.Split(*cluster, ","), *join, getSnapshot, proposeC, confChangeC)
kvs = newKVStore(<-snapshotterReady, proposeC, commitC, errorC)
// the key-value http handler will propose updates to raft
serveHttpKVAPI(*kvport, proposeC, confChangeC, commitC, errorC)
serveHttpKVAPI(kvs, *kvport, confChangeC, errorC)
}

97
contrib/raftexample/raft.go
View File

@ -43,12 +43,13 @@ type raftNode struct {
commitC chan<- *string // entries committed to log (k,v)
errorC chan<- error // errors from raft session
id int // client ID for raft session
peers []string // raft peer URLs
join bool // node is joining an existing cluster
waldir string // path to WAL directory
snapdir string // path to snapshot directory
lastIndex uint64 // index of log at start
id int // client ID for raft session
peers []string // raft peer URLs
join bool // node is joining an existing cluster
waldir string // path to WAL directory
snapdir string // path to snapshot directory
getSnapshot func() ([]byte, error)
lastIndex uint64 // index of log at start
confState raftpb.ConfState
snapshotIndex uint64
@ -58,20 +59,26 @@ type raftNode struct {
node raft.Node
raftStorage *raft.MemoryStorage
wal *wal.WAL
snapshotter *snap.Snapshotter
transport *rafthttp.Transport
stopc chan struct{} // signals proposal channel closed
httpstopc chan struct{} // signals http server to shutdown
httpdonec chan struct{} // signals http server shutdown complete
snapshotter *snap.Snapshotter
snapshotterReady chan *snap.Snapshotter // signals when snapshotter is ready
snapCount uint64
transport *rafthttp.Transport
stopc chan struct{} // signals proposal channel closed
httpstopc chan struct{} // signals http server to shutdown
httpdonec chan struct{} // signals http server shutdown complete
}
var defaultSnapCount uint64 = 10000
// newRaftNode initiates a raft instance and returns a committed log entry
// channel and error channel. Proposals for log updates are sent over the
// provided the proposal channel. All log entries are replayed over the
// commit channel, followed by a nil message (to indicate the channel is
// current), then new log entries. To shutdown, close proposeC and read errorC.
func newRaftNode(id int, peers []string, join bool, proposeC <-chan string,
confChangeC <-chan raftpb.ConfChange) (<-chan *string, <-chan error) {
func newRaftNode(id int, peers []string, join bool, getSnapshot func() ([]byte, error), proposeC <-chan string,
confChangeC <-chan raftpb.ConfChange) (<-chan *string, <-chan error, <-chan *snap.Snapshotter) {
commitC := make(chan *string)
errorC := make(chan error)
@ -86,14 +93,18 @@ func newRaftNode(id int, peers []string, join bool, proposeC <-chan string,
join: join,
waldir: fmt.Sprintf("raftexample-%d", id),
snapdir: fmt.Sprintf("raftexample-%d-snap", id),
getSnapshot: getSnapshot,
raftStorage: raft.NewMemoryStorage(),
snapCount: defaultSnapCount,
stopc: make(chan struct{}),
httpstopc: make(chan struct{}),
httpdonec: make(chan struct{}),
snapshotterReady: make(chan *snap.Snapshotter, 1),
// rest of structure populated after WAL replay
}
go rc.startRaft()
return commitC, errorC
return commitC, errorC, rc.snapshotterReady
}
func (rc *raftNode) saveSnap(snap raftpb.Snapshot) error {
@ -229,9 +240,11 @@ func (rc *raftNode) startRaft() {
log.Fatalf("raftexample: cannot create dir for snapshot (%v)", err)
}
}
rc.snapshotter = snap.New(rc.snapdir)
rc.snapshotterReady <- rc.snapshotter
oldwal := wal.Exist(rc.waldir)
rc.wal = rc.replayWAL()
rc.snapshotter = snap.New(rc.snapdir)
rpeers := make([]raft.Peer, len(rc.peers))
for i := range rpeers {
@ -293,6 +306,56 @@ func (rc *raftNode) stopHTTP() {
<-rc.httpdonec
}
func (rc *raftNode) publishSnapshot(snapshotToSave raftpb.Snapshot) {
if raft.IsEmptySnap(snapshotToSave) {
return
}
log.Printf("publishing snapshot at index %d", rc.snapshotIndex)
defer log.Printf("finished publishing snapshot at index %d", rc.snapshotIndex)
if snapshotToSave.Metadata.Index <= rc.appliedIndex {
log.Fatalf("snapshot index [%d] should > progress.appliedIndex [%d] + 1", snapshotToSave.Metadata.Index, rc.appliedIndex)
}
rc.commitC <- nil // trigger kvstore to load snapshot
rc.confState = snapshotToSave.Metadata.ConfState
rc.snapshotIndex = snapshotToSave.Metadata.Index
rc.appliedIndex = snapshotToSave.Metadata.Index
}
var snapshotCatchUpEntriesN uint64 = 10000
func (rc *raftNode) maybeTriggerSnapshot() {
if rc.appliedIndex-rc.snapshotIndex <= rc.snapCount {
return
}
log.Printf("start snapshot [applied index: %d | last snapshot index: %d]", rc.appliedIndex, rc.snapshotIndex)
data, err := rc.getSnapshot()
if err != nil {
log.Panic(err)
}
snap, err := rc.raftStorage.CreateSnapshot(rc.appliedIndex, &rc.confState, data)
if err != nil {
panic(err)
}
if err := rc.saveSnap(snap); err != nil {
panic(err)
}
compactIndex := uint64(1)
if rc.appliedIndex > snapshotCatchUpEntriesN {
compactIndex = rc.appliedIndex - snapshotCatchUpEntriesN
}
if err := rc.raftStorage.Compact(compactIndex); err != nil {
panic(err)
}
log.Printf("compacted log at index %d", compactIndex)
rc.snapshotIndex = rc.appliedIndex
}
func (rc *raftNode) serveChannels() {
snap, err := rc.raftStorage.Snapshot()
if err != nil {
@ -347,15 +410,15 @@ func (rc *raftNode) serveChannels() {
if !raft.IsEmptySnap(rd.Snapshot) {
rc.saveSnap(rd.Snapshot)
rc.raftStorage.ApplySnapshot(rd.Snapshot)
rc.publishSnapshot(rd.Snapshot)
}
rc.raftStorage.Append(rd.Entries)
rc.transport.Send(rd.Messages)
// TODO: apply snapshot
if ok := rc.publishEntries(rc.entriesToApply(rd.CommittedEntries)); !ok {
rc.stop()
return
}
// TODO: trigger snapshot
rc.maybeTriggerSnapshot()
rc.node.Advance()
case err := <-rc.transport.ErrorC:

2
contrib/raftexample/raftexample_test.go
View File

@ -50,7 +50,7 @@ func newCluster(n int) *cluster {
os.RemoveAll(fmt.Sprintf("raftexample-%d-snap", i+1))
clus.proposeC[i] = make(chan string, 1)
clus.confChangeC[i] = make(chan raftpb.ConfChange, 1)
clus.commitC[i], clus.errorC[i] = newRaftNode(i+1, clus.peers, false, clus.proposeC[i], clus.confChangeC[i])
clus.commitC[i], clus.errorC[i], _ = newRaftNode(i+1, clus.peers, false, nil, clus.proposeC[i], clus.confChangeC[i])
}
return clus