etcdserver: initial read index implementation

etcdserver/raft.go

@@ -103,6 +103,9 @@ type raftNode struct {
 	// a chan to send out apply
 	applyc chan apply
 
+	// a chan to send out readState
+	readStateC chan raft.ReadState
+
 	// TODO: remove the etcdserver related logic from raftNode
 	// TODO: add a state machine interface to apply the commit entries
 	// and do snapshot/recover
@@ -196,6 +199,13 @@ func (r *raftNode) start(s *EtcdServer) {
 					}
 				}
 
+				if rd.ReadState.Index != 0 {
+					select {
+					case r.readStateC <- rd.ReadState:
+					default:
+					}
+				}
+
 				raftDone := make(chan struct{}, 1)
 				ap := apply{
 					entries:  rd.CommittedEntries,

etcdserver/server.go

@@ -173,7 +173,9 @@ type EtcdServer struct {
 
 	snapCount uint64
 
-	w          wait.Wait
+	w         wait.Wait
+	readwaitc chan chan struct{}
+
 	stop       chan struct{}
 	done       chan struct{}
 	errorc     chan error
@@ -190,12 +192,15 @@ type EtcdServer struct {
 	applyV3 applierV3
 	// applyV3Base is the core applier without auth or quotas
 	applyV3Base applierV3
-	kv          mvcc.ConsistentWatchableKV
-	lessor      lease.Lessor
-	bemu        sync.Mutex
-	be          backend.Backend
-	authStore   auth.AuthStore
-	alarmStore  *alarm.AlarmStore
+
+	applyNotify chan struct{}
+
+	kv         mvcc.ConsistentWatchableKV
+	lessor     lease.Lessor
+	bemu       sync.Mutex
+	be         backend.Backend
+	authStore  auth.AuthStore
+	alarmStore *alarm.AlarmStore
 
 	stats  *stats.ServerStats
 	lstats *stats.LeaderStats
@@ -382,6 +387,7 @@ func NewServer(cfg *ServerConfig) (srv *EtcdServer, err error) {
 			ticker:      time.Tick(time.Duration(cfg.TickMs) * time.Millisecond),
 			raftStorage: s,
 			storage:     NewStorage(w, ss),
+			readStateC:  make(chan raft.ReadState, 1),
 		},
 		id:            id,
 		attributes:    membership.Attributes{Name: cfg.Name, ClientURLs: cfg.ClientURLs.StringSlice()},
@@ -393,6 +399,7 @@ func NewServer(cfg *ServerConfig) (srv *EtcdServer, err error) {
 		reqIDGen:      idutil.NewGenerator(uint16(id), time.Now()),
 		forceVersionC: make(chan struct{}),
 		msgSnapC:      make(chan raftpb.Message, maxInFlightMsgSnap),
+		applyNotify:   make(chan struct{}, 0),
 	}
 
 	srv.applyV2 = &applierV2store{store: srv.store, cluster: srv.cluster}
@@ -464,6 +471,7 @@ func (s *EtcdServer) Start() {
 	go s.purgeFile()
 	go monitorFileDescriptor(s.done)
 	go s.monitorVersions()
+	go s.linearizableReadLoop()
 }
 
 // start prepares and starts server in a new goroutine. It is no longer safe to
@@ -475,6 +483,7 @@ func (s *EtcdServer) start() {
 		s.snapCount = DefaultSnapCount
 	}
 	s.w = wait.New()
+	s.readwaitc = make(chan chan struct{}, 1024)
 	s.done = make(chan struct{})
 	s.stop = make(chan struct{})
 	if s.ClusterVersion() != nil {
@@ -633,6 +642,12 @@ func (s *EtcdServer) applyAll(ep *etcdProgress, apply *apply) {
 	// snapshot. or applied index might be greater than the last index in raft
 	// storage, since the raft routine might be slower than apply routine.
 	<-apply.raftDone
+
+	select {
+	case s.applyNotify <- struct{}{}:
+	default:
+	}
+
 	s.triggerSnapshot(ep)
 	select {
 	// snapshot requested via send()

etcdserver/v3_server.go

@@ -15,6 +15,8 @@
 package etcdserver
 
 import (
+	"bytes"
+	"encoding/binary"
 	"strconv"
 	"strings"
 	"time"
@@ -24,6 +26,7 @@ import (
 	"github.com/coreos/etcd/lease"
 	"github.com/coreos/etcd/lease/leasehttp"
 	"github.com/coreos/etcd/mvcc"
+	"github.com/coreos/etcd/raft"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc/metadata"
 )
@@ -84,26 +87,31 @@ type Authenticator interface {
 }
 
 func (s *EtcdServer) Range(ctx context.Context, r *pb.RangeRequest) (*pb.RangeResponse, error) {
-	if r.Serializable {
-		var resp *pb.RangeResponse
-		var err error
-		chk := func(ai *auth.AuthInfo) error {
-			return s.authStore.IsRangePermitted(ai, r.Key, r.RangeEnd)
+	if !r.Serializable {
+		ok := make(chan struct{})
+
+		select {
+		case s.readwaitc <- ok:
+		case <-ctx.Done():
+			return nil, ctx.Err()
 		}
-		get := func() { resp, err = s.applyV3Base.Range(noTxn, r) }
-		if serr := s.doSerialize(ctx, chk, get); serr != nil {
-			return nil, serr
+
+		select {
+		case <-ok:
+		case <-ctx.Done():
+			return nil, ctx.Err()
 		}
-		return resp, err
 	}
-	result, err := s.processInternalRaftRequest(ctx, pb.InternalRaftRequest{Range: r})
-	if err != nil {
-		return nil, err
+	var resp *pb.RangeResponse
+	var err error
+	chk := func(ai *auth.AuthInfo) error {
+		return s.authStore.IsRangePermitted(ai, r.Key, r.RangeEnd)
 	}
-	if result.err != nil {
-		return nil, result.err
+	get := func() { resp, err = s.applyV3Base.Range(noTxn, r) }
+	if serr := s.doSerialize(ctx, chk, get); serr != nil {
+		return nil, serr
 	}
-	return result.resp.(*pb.RangeResponse), nil
+	return resp, err
 }
 
 func (s *EtcdServer) Put(ctx context.Context, r *pb.PutRequest) (*pb.PutResponse, error) {
@@ -604,3 +612,49 @@ func (s *EtcdServer) processInternalRaftRequest(ctx context.Context, r pb.Intern
 
 // Watchable returns a watchable interface attached to the etcdserver.
 func (s *EtcdServer) Watchable() mvcc.WatchableKV { return s.KV() }
+
+func (s *EtcdServer) linearizableReadLoop() {
+	var rs raft.ReadState
+	oks := make([]chan struct{}, 0, 256)
+	ctx := make([]byte, 8)
+
+	for lc := uint64(0); ; lc++ {
+		binary.BigEndian.PutUint64(ctx, lc)
+
+		for (len(s.readwaitc) > 0 && len(oks) < 256) || (len(s.readwaitc) == 0 && len(oks) == 0) {
+			select {
+			case ok := <-s.readwaitc:
+				oks = append(oks, ok)
+			}
+		}
+
+		if err := s.r.ReadIndex(context.Background(), ctx); err != nil {
+			continue
+		}
+		select {
+		case rs = <-s.r.readStateC:
+			if !bytes.Equal(rs.RequestCtx, ctx) {
+				continue
+			}
+		case <-time.After(time.Second):
+			continue
+		}
+
+		for {
+			ai := s.getAppliedIndex()
+			if ai >= rs.Index {
+				// unblock all the l-read that happened before we requested the
+				// read index
+				for _, ok := range oks {
+					close(ok)
+				}
+				oks = make([]chan struct{}, 0, 256)
+				break
+			}
+			select {
+			case <-s.applyNotify:
+			case <-time.After(10 * time.Millisecond):
+			}
+		}
+	}
+}