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groups.go
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groups.go
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/*
* Copyright 2016-2018 Dgraph Labs, Inc. and Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package worker
import (
"context"
"fmt"
"io"
"sort"
"sync"
"sync/atomic"
"time"
"github.com/dgraph-io/badger/v2"
badgerpb "github.com/dgraph-io/badger/v2/pb"
"github.com/dgraph-io/badger/v2/y"
"github.com/dgraph-io/dgo/v2/protos/api"
"github.com/dgraph-io/dgraph/conn"
"github.com/dgraph-io/dgraph/ee/enc"
"github.com/dgraph-io/dgraph/protos/pb"
"github.com/dgraph-io/dgraph/raftwal"
"github.com/dgraph-io/dgraph/schema"
"github.com/dgraph-io/dgraph/x"
"github.com/golang/glog"
"github.com/golang/protobuf/proto"
"github.com/pkg/errors"
)
type groupi struct {
x.SafeMutex
// TODO: Is this context being used?
ctx context.Context
cancel context.CancelFunc
state *pb.MembershipState
Node *node
gid uint32
tablets map[string]*pb.Tablet
triggerCh chan struct{} // Used to trigger membership sync
blockDeletes *sync.Mutex // Ensure that deletion won't happen when move is going on.
closer *y.Closer
// Group checksum is used to determine if the tablets served by the groups have changed from
// the membership information that the Alpha has. If so, Alpha cannot service a read.
deltaChecksum uint64 // Checksum received by OracleDelta.
membershipChecksum uint64 // Checksum received by MembershipState.
}
var gr = &groupi{
blockDeletes: new(sync.Mutex),
tablets: make(map[string]*pb.Tablet),
}
func groups() *groupi {
return gr
}
// StartRaftNodes will read the WAL dir, create the RAFT groups,
// and either start or restart RAFT nodes.
// This function triggers RAFT nodes to be created, and is the entrance to the RAFT
// world from main.go.
func StartRaftNodes(walStore *badger.DB, bindall bool) {
gr.ctx, gr.cancel = context.WithCancel(context.Background())
if len(x.WorkerConfig.MyAddr) == 0 {
x.WorkerConfig.MyAddr = fmt.Sprintf("localhost:%d", workerPort())
} else {
// check if address is valid or not
ok := x.ValidateAddress(x.WorkerConfig.MyAddr)
x.AssertTruef(ok, "%s is not valid address", x.WorkerConfig.MyAddr)
if !bindall {
glog.Errorln("--my flag is provided without bindall, Did you forget to specify bindall?")
}
}
x.AssertTruef(len(x.WorkerConfig.ZeroAddr) > 0, "Providing dgraphzero address is mandatory.")
x.AssertTruef(x.WorkerConfig.ZeroAddr != x.WorkerConfig.MyAddr,
"Dgraph Zero address and Dgraph address (IP:Port) can't be the same.")
if x.WorkerConfig.RaftId == 0 {
id, err := raftwal.RaftId(walStore)
x.Check(err)
x.WorkerConfig.RaftId = id
// If the w directory already contains raft information, ignore the proposed
// group ID stored inside the p directory.
if id > 0 {
x.WorkerConfig.ProposedGroupId = 0
}
}
glog.Infof("Current Raft Id: %#x\n", x.WorkerConfig.RaftId)
// Successfully connect with dgraphzero, before doing anything else.
// Connect with Zero leader and figure out what group we should belong to.
m := &pb.Member{Id: x.WorkerConfig.RaftId, GroupId: x.WorkerConfig.ProposedGroupId,
Addr: x.WorkerConfig.MyAddr}
if m.GroupId > 0 {
m.ForceGroupId = true
}
var connState *pb.ConnectionState
var err error
for { // Keep on retrying. See: https://github.com/dgraph-io/dgraph/issues/2289
pl := gr.connToZeroLeader()
if pl == nil {
continue
}
zc := pb.NewZeroClient(pl.Get())
connState, err = zc.Connect(gr.ctx, m)
if err == nil || x.ShouldCrash(err) {
break
}
}
x.CheckfNoTrace(err)
if connState.GetMember() == nil || connState.GetState() == nil {
x.Fatalf("Unable to join cluster via dgraphzero")
}
glog.Infof("Connected to group zero. Assigned group: %+v\n", connState.GetMember().GetGroupId())
x.WorkerConfig.RaftId = connState.GetMember().GetId()
glog.Infof("Raft Id after connection to Zero: %#x\n", x.WorkerConfig.RaftId)
// This timestamp would be used for reading during snapshot after bulk load.
// The stream is async, we need this information before we start or else replica might
// not get any data.
gr.applyState(connState.GetState())
gid := gr.groupId()
gr.triggerCh = make(chan struct{}, 1)
// Initialize DiskStorage and pass it along.
store := raftwal.Init(walStore, x.WorkerConfig.RaftId, gid)
gr.Node = newNode(store, gid, x.WorkerConfig.RaftId, x.WorkerConfig.MyAddr)
x.Checkf(schema.LoadFromDb(), "Error while initializing schema")
raftServer.UpdateNode(gr.Node.Node)
gr.Node.InitAndStartNode()
x.UpdateHealthStatus(true)
glog.Infof("Server is ready")
gr.closer = y.NewCloser(3) // Match CLOSER:1 in this file.
go gr.sendMembershipUpdates()
go gr.receiveMembershipUpdates()
go gr.processOracleDeltaStream()
gr.informZeroAboutTablets()
gr.proposeInitialSchema()
gr.proposeInitialTypes()
}
func (g *groupi) informZeroAboutTablets() {
// Before we start this Alpha, let's pick up all the predicates we have in our postings
// directory, and ask Zero if we are allowed to serve it. Do this irrespective of whether
// this node is the leader or the follower, because this early on, we might not have
// figured that out.
ticker := time.NewTicker(time.Second)
defer ticker.Stop()
for range ticker.C {
failed := false
preds := schema.State().Predicates()
for _, pred := range preds {
if tablet, err := g.Tablet(pred); err != nil {
failed = true
glog.Errorf("Error while getting tablet for pred %q: %v", pred, err)
} else if tablet == nil {
failed = true
}
}
if !failed {
glog.V(1).Infof("Done informing Zero about the %d tablets I have", len(preds))
return
}
}
}
func (g *groupi) proposeInitialTypes() {
initialTypes := schema.InitialTypes()
for _, t := range initialTypes {
if _, ok := schema.State().GetType(t.TypeName); ok {
continue
}
g.upsertSchema(nil, t)
}
}
func (g *groupi) proposeInitialSchema() {
initialSchema := schema.InitialSchema()
for _, s := range initialSchema {
if gid, err := g.BelongsToReadOnly(s.Predicate, 0); err != nil {
glog.Errorf("Error getting tablet for predicate %s. Will force schema proposal.",
s.Predicate)
g.upsertSchema(s, nil)
} else if gid == 0 {
g.upsertSchema(s, nil)
} else if curr, _ := schema.State().Get(s.Predicate); gid == g.groupId() &&
!proto.Equal(s, &curr) {
// If this tablet is served to the group, do not upsert the schema unless the
// stored schema and the proposed one are different.
g.upsertSchema(s, nil)
} else {
// The schema for this predicate has already been proposed.
glog.V(1).Infof("Skipping initial schema upsert for predicate %s", s.Predicate)
continue
}
}
}
func (g *groupi) upsertSchema(sch *pb.SchemaUpdate, typ *pb.TypeUpdate) {
// Propose schema mutation.
var m pb.Mutations
// schema for a reserved predicate is not changed once set.
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
ts, err := Timestamps(ctx, &pb.Num{Val: 1})
cancel()
if err != nil {
glog.Errorf("error while requesting timestamp for schema %v: %v", sch, err)
return
}
m.StartTs = ts.StartId
if sch != nil {
m.Schema = append(m.Schema, sch)
}
if typ != nil {
m.Types = append(m.Types, typ)
}
// This would propose the schema mutation and make sure some node serves this predicate
// and has the schema defined above.
for {
_, err := MutateOverNetwork(gr.ctx, &m)
if err == nil {
break
}
glog.Errorf("Error while proposing initial schema: %v\n", err)
time.Sleep(100 * time.Millisecond)
}
}
// No locks are acquired while accessing this function.
// Don't acquire RW lock during this, otherwise we might deadlock.
func (g *groupi) groupId() uint32 {
return atomic.LoadUint32(&g.gid)
}
// MaxLeaseId returns the maximum UID that has been leased.
func MaxLeaseId() uint64 {
g := groups()
g.RLock()
defer g.RUnlock()
if g.state == nil {
return 0
}
return g.state.MaxLeaseId
}
// GetMembershipState returns the current membership state.
func GetMembershipState() *pb.MembershipState {
g := groups()
g.RLock()
defer g.RUnlock()
return proto.Clone(g.state).(*pb.MembershipState)
}
// UpdateMembershipState contacts zero for an update on membership state.
func UpdateMembershipState(ctx context.Context) error {
g := groups()
p := g.Leader(0)
if p == nil {
return errors.Errorf("Don't have the address of any dgraphzero server")
}
c := pb.NewZeroClient(p.Get())
state, err := c.Connect(ctx, &pb.Member{ClusterInfoOnly: true})
if err != nil {
return err
}
g.applyState(state.GetState())
return nil
}
func (g *groupi) applyState(state *pb.MembershipState) {
x.AssertTrue(state != nil)
g.Lock()
defer g.Unlock()
// We don't update state if we get any old state. Counter stores the raftindex of
// last update. For leader changes at zero since we don't propose, state can get
// updated at same counter value. So ignore only if counter is less.
if g.state != nil && g.state.Counter > state.Counter {
return
}
oldState := g.state
g.state = state
// Sometimes this can cause us to lose latest tablet info, but that shouldn't cause any issues.
var foundSelf bool
g.tablets = make(map[string]*pb.Tablet)
for gid, group := range g.state.Groups {
for _, member := range group.Members {
if x.WorkerConfig.RaftId == member.Id {
foundSelf = true
atomic.StoreUint32(&g.gid, gid)
}
if x.WorkerConfig.MyAddr != member.Addr {
conn.GetPools().Connect(member.Addr)
}
}
for _, tablet := range group.Tablets {
g.tablets[tablet.Predicate] = tablet
}
if gid == g.groupId() {
glog.V(3).Infof("group %d checksum: %d", g.groupId(), group.Checksum)
atomic.StoreUint64(&g.membershipChecksum, group.Checksum)
}
}
for _, member := range g.state.Zeros {
if x.WorkerConfig.MyAddr != member.Addr {
conn.GetPools().Connect(member.Addr)
}
}
if !foundSelf {
// I'm not part of this cluster. I should crash myself.
glog.Fatalf("Unable to find myself [id:%d group:%d] in membership state: %+v. Goodbye!",
g.Node.Id, g.groupId(), state)
}
// While restarting we fill Node information after retrieving initial state.
if g.Node != nil {
// Lets have this block before the one that adds the new members, else we may end up
// removing a freshly added node.
for _, member := range g.state.GetRemoved() {
// TODO: This leader check can be done once instead of repeatedly.
if member.GetGroupId() == g.Node.gid && g.Node.AmLeader() {
go func() {
// Don't try to remove a member if it's already marked as removed in
// the membership state and is not a current peer of the node.
_, isPeer := g.Node.Peer(member.GetId())
// isPeer should only be true if the rmeoved node is not the same as this node.
isPeer = isPeer && member.GetId() != g.Node.RaftContext.Id
for _, oldMember := range oldState.GetRemoved() {
if oldMember.GetId() == member.GetId() && !isPeer {
return
}
}
if err := g.Node.ProposePeerRemoval(
context.Background(), member.GetId()); err != nil {
glog.Errorf("Error while proposing node removal: %+v", err)
}
}()
}
}
conn.GetPools().RemoveInvalid(g.state)
}
}
func (g *groupi) ServesGroup(gid uint32) bool {
return g.groupId() == gid
}
func (g *groupi) ChecksumsMatch(ctx context.Context) error {
if atomic.LoadUint64(&g.deltaChecksum) == atomic.LoadUint64(&g.membershipChecksum) {
return nil
}
t := time.NewTicker(100 * time.Millisecond)
defer t.Stop()
for {
select {
case <-t.C:
if atomic.LoadUint64(&g.deltaChecksum) == atomic.LoadUint64(&g.membershipChecksum) {
return nil
}
case <-ctx.Done():
return errors.Errorf("Group checksum mismatch for id: %d", g.groupId())
}
}
}
func (g *groupi) BelongsTo(key string) (uint32, error) {
if tablet, err := g.Tablet(key); err != nil {
return 0, err
} else if tablet != nil {
return tablet.GroupId, nil
}
return 0, nil
}
// BelongsToReadOnly acts like BelongsTo except it does not ask zero to serve
// the tablet for key if no group is currently serving it.
// The ts passed should be the start ts of the query, so this method can compare that against a
// tablet move timestamp. If the tablet was moved to this group after the start ts of the query, we
// should reject that query.
func (g *groupi) BelongsToReadOnly(key string, ts uint64) (uint32, error) {
g.RLock()
tablet := g.tablets[key]
g.RUnlock()
if tablet != nil {
if ts > 0 && ts < tablet.MoveTs {
return 0, errors.Errorf("StartTs: %d is from before MoveTs: %d for pred: %q",
ts, tablet.MoveTs, key)
}
return tablet.GetGroupId(), nil
}
// We don't know about this tablet. Talk to dgraphzero to find out who is
// serving this tablet.
pl := g.connToZeroLeader()
zc := pb.NewZeroClient(pl.Get())
tablet = &pb.Tablet{
Predicate: key,
ReadOnly: true,
}
out, err := zc.ShouldServe(context.Background(), tablet)
if err != nil {
glog.Errorf("Error while ShouldServe grpc call %v", err)
return 0, err
}
if out.GetGroupId() == 0 {
return 0, nil
}
g.Lock()
defer g.Unlock()
g.tablets[key] = out
if out != nil && ts > 0 && ts < out.MoveTs {
return 0, errors.Errorf("StartTs: %d is from before MoveTs: %d for pred: %q",
ts, out.MoveTs, key)
}
return out.GetGroupId(), nil
}
func (g *groupi) ServesTablet(key string) (bool, error) {
if tablet, err := g.Tablet(key); err != nil {
return false, err
} else if tablet != nil && tablet.GroupId == groups().groupId() {
return true, nil
}
return false, nil
}
// Do not modify the returned Tablet
func (g *groupi) Tablet(key string) (*pb.Tablet, error) {
emptyTablet := pb.Tablet{}
// TODO: Remove all this later, create a membership state and apply it
g.RLock()
tablet, ok := g.tablets[key]
g.RUnlock()
if ok {
return tablet, nil
}
// We don't know about this tablet.
// Check with dgraphzero if we can serve it.
pl := g.connToZeroLeader()
zc := pb.NewZeroClient(pl.Get())
tablet = &pb.Tablet{GroupId: g.groupId(), Predicate: key}
out, err := zc.ShouldServe(context.Background(), tablet)
if err != nil {
glog.Errorf("Error while ShouldServe grpc call %v", err)
return &emptyTablet, err
}
// Do not store tablets with group ID 0, as they are just dummy tablets for
// predicates that do no exist.
if out.GroupId > 0 {
g.Lock()
g.tablets[key] = out
g.Unlock()
}
if out.GroupId == groups().groupId() {
glog.Infof("Serving tablet for: %v\n", key)
}
return out, nil
}
func (g *groupi) HasMeInState() bool {
g.RLock()
defer g.RUnlock()
if g.state == nil {
return false
}
group, has := g.state.Groups[g.groupId()]
if !has {
return false
}
_, has = group.Members[g.Node.Id]
return has
}
// Returns 0, 1, or 2 valid server addrs.
func (g *groupi) AnyTwoServers(gid uint32) []string {
g.RLock()
defer g.RUnlock()
if g.state == nil {
return []string{}
}
group, has := g.state.Groups[gid]
if !has {
return []string{}
}
var res []string
for _, m := range group.Members {
// map iteration gives us members in no particular order.
res = append(res, m.Addr)
if len(res) >= 2 {
break
}
}
return res
}
func (g *groupi) members(gid uint32) map[uint64]*pb.Member {
g.RLock()
defer g.RUnlock()
if g.state == nil {
return nil
}
if gid == 0 {
return g.state.Zeros
}
group, has := g.state.Groups[gid]
if !has {
return nil
}
return group.Members
}
func (g *groupi) AnyServer(gid uint32) *conn.Pool {
members := g.members(gid)
for _, m := range members {
pl, err := conn.GetPools().Get(m.Addr)
if err == nil {
return pl
}
}
return nil
}
func (g *groupi) MyPeer() (uint64, bool) {
members := g.members(g.groupId())
for _, m := range members {
if m.Id != g.Node.Id {
return m.Id, true
}
}
return 0, false
}
// Leader will try to return the leader of a given group, based on membership information.
// There is currently no guarantee that the returned server is the leader of the group.
func (g *groupi) Leader(gid uint32) *conn.Pool {
members := g.members(gid)
if members == nil {
return nil
}
for _, m := range members {
if m.Leader {
if pl, err := conn.GetPools().Get(m.Addr); err == nil {
return pl
}
}
}
return nil
}
func (g *groupi) KnownGroups() (gids []uint32) {
g.RLock()
defer g.RUnlock()
if g.state == nil {
return
}
for gid := range g.state.Groups {
gids = append(gids, gid)
}
return
}
// KnownGroups returns the known groups using the global groupi instance.
func KnownGroups() []uint32 {
return groups().KnownGroups()
}
// GroupId returns the group to which this worker belongs to.
func GroupId() uint32 {
return groups().groupId()
}
func (g *groupi) triggerMembershipSync() {
// It's ok if we miss the trigger, periodic membership sync runs every minute.
select {
case g.triggerCh <- struct{}{}:
// It's ok to ignore it, since we would be sending update of a later state
default:
}
}
const connBaseDelay = 100 * time.Millisecond
func (g *groupi) connToZeroLeader() *conn.Pool {
pl := g.Leader(0)
if pl != nil {
return pl
}
glog.V(1).Infof("No healthy Zero leader found. Trying to find a Zero leader...")
getLeaderConn := func(zc pb.ZeroClient) *conn.Pool {
ctx, cancel := context.WithTimeout(g.ctx, 10*time.Second)
defer cancel()
connState, err := zc.Connect(ctx, &pb.Member{ClusterInfoOnly: true})
if err != nil || connState == nil {
glog.V(1).Infof("While retrieving Zero leader info. Error: %v. Retrying...", err)
return nil
}
for _, mz := range connState.State.GetZeros() {
if mz.Leader {
return conn.GetPools().Connect(mz.GetAddr())
}
}
return nil
}
// No leader found. Let's get the latest membership state from Zero.
delay := connBaseDelay
maxHalfDelay := time.Second
for { // Keep on retrying. See: https://github.com/dgraph-io/dgraph/issues/2289
time.Sleep(delay)
if delay <= maxHalfDelay {
delay *= 2
}
pl := g.AnyServer(0)
if pl == nil {
pl = conn.GetPools().Connect(x.WorkerConfig.ZeroAddr)
}
if pl == nil {
glog.V(1).Infof("No healthy Zero server found. Retrying...")
continue
}
zc := pb.NewZeroClient(pl.Get())
if pl := getLeaderConn(zc); pl != nil {
glog.V(1).Infof("Found connection to leader: %s", pl.Addr)
return pl
}
glog.V(1).Infof("Unable to connect to a healthy Zero leader. Retrying...")
}
}
func (g *groupi) doSendMembership(tablets map[string]*pb.Tablet) error {
leader := g.Node.AmLeader()
member := &pb.Member{
Id: x.WorkerConfig.RaftId,
GroupId: g.groupId(),
Addr: x.WorkerConfig.MyAddr,
Leader: leader,
LastUpdate: uint64(time.Now().Unix()),
}
group := &pb.Group{
Members: make(map[uint64]*pb.Member),
}
group.Members[member.Id] = member
if leader {
// Do not send tablet information, if I'm not the leader.
group.Tablets = tablets
if snap, err := g.Node.Snapshot(); err == nil {
group.SnapshotTs = snap.ReadTs
}
}
pl := g.connToZeroLeader()
if pl == nil {
return errNoConnection
}
c := pb.NewZeroClient(pl.Get())
ctx, cancel := context.WithTimeout(g.ctx, 10*time.Second)
defer cancel()
reply, err := c.UpdateMembership(ctx, group)
if err != nil {
return err
}
if string(reply.GetData()) == "OK" {
return nil
}
return errors.Errorf(string(reply.GetData()))
}
// sendMembershipUpdates sends the membership update to Zero leader. If this Alpha is the leader, it
// would also calculate the tablet sizes and send them to Zero.
func (g *groupi) sendMembershipUpdates() {
defer g.closer.Done() // CLOSER:1
ticker := time.NewTicker(time.Second)
defer ticker.Stop()
consumeTriggers := func() {
for {
select {
case <-g.triggerCh:
default:
return
}
}
}
g.triggerMembershipSync() // Ticker doesn't start immediately
var lastSent time.Time
for {
select {
case <-g.closer.HasBeenClosed():
return
case <-ticker.C:
if time.Since(lastSent) > 10*time.Second {
// On start of node if it becomes a leader, we would send tablets size for sure.
g.triggerMembershipSync()
}
case <-g.triggerCh:
// Let's send update even if not leader, zero will know that this node is still active.
// We don't need to send tablet information everytime. So, let's only send it when we
// calculate it.
consumeTriggers()
if err := g.doSendMembership(nil); err != nil {
glog.Errorf("While sending membership update: %v", err)
} else {
lastSent = time.Now()
}
}
}
}
// receiveMembershipUpdates receives membership updates from ANY Zero server. This is the main
// connection which tells Alpha about the state of the cluster, including the latest Zero leader.
// All the other connections to Zero, are only made only to the leader.
func (g *groupi) receiveMembershipUpdates() {
defer g.closer.Done() // CLOSER:1
ticker := time.NewTicker(10 * time.Second)
defer ticker.Stop()
START:
select {
case <-g.closer.HasBeenClosed():
return
default:
}
pl := g.connToZeroLeader()
// We should always have some connection to dgraphzero.
if pl == nil {
glog.Warningln("Membership update: No Zero server known.")
time.Sleep(time.Second)
goto START
}
glog.Infof("Got address of a Zero leader: %s", pl.Addr)
c := pb.NewZeroClient(pl.Get())
ctx, cancel := context.WithCancel(context.Background())
stream, err := c.StreamMembership(ctx, &api.Payload{})
if err != nil {
glog.Errorf("Error while calling update %v\n", err)
time.Sleep(time.Second)
goto START
}
stateCh := make(chan *pb.MembershipState, 10)
go func() {
glog.Infof("Starting a new membership stream receive from %s.", pl.Addr)
for i := 0; ; i++ {
// Blocking, should return if sending on stream fails(Need to verify).
state, err := stream.Recv()
if err != nil || state == nil {
if err == io.EOF {
glog.Infoln("Membership sync stream closed.")
} else {
glog.Errorf("Unable to sync memberships. Error: %v. State: %v", err, state)
}
// If zero server is lagging behind leader.
if ctx.Err() == nil {
cancel()
}
return
}
if i == 0 {
glog.Infof("Received first state update from Zero: %+v", state)
}
select {
case stateCh <- state:
case <-ctx.Done():
return
}
}
}()
lastRecv := time.Now()
OUTER:
for {
select {
case <-g.closer.HasBeenClosed():
if err := stream.CloseSend(); err != nil {
glog.Errorf("Error closing send stream: %+v", err)
}
break OUTER
case <-ctx.Done():
if err := stream.CloseSend(); err != nil {
glog.Errorf("Error closing send stream: %+v", err)
}
break OUTER
case state := <-stateCh:
lastRecv = time.Now()
g.applyState(state)
case <-ticker.C:
if time.Since(lastRecv) > 10*time.Second {
// Zero might have gone under partition. We should recreate our connection.
glog.Warningf("No membership update for 10s. Closing connection to Zero.")
if err := stream.CloseSend(); err != nil {
glog.Errorf("Error closing send stream: %+v", err)
}
break OUTER
}
}
}
cancel()
goto START
}
// processOracleDeltaStream is used to process oracle delta stream from Zero.
// Zero sends information about aborted/committed transactions and maxPending.
func (g *groupi) processOracleDeltaStream() {
defer g.closer.Done() // CLOSER:1
ticker := time.NewTicker(time.Second)
defer ticker.Stop()
blockingReceiveAndPropose := func() {
glog.Infof("Leader idx=%#x of group=%d is connecting to Zero for txn updates\n",
g.Node.Id, g.groupId())
pl := g.connToZeroLeader()
if pl == nil {
glog.Warningln("Oracle delta stream: No Zero leader known.")
time.Sleep(time.Second)
return
}
glog.Infof("Got Zero leader: %s", pl.Addr)
// The following code creates a stream. Then runs a goroutine to pick up events from the
// stream and pushes them to a channel. The main loop loops over the channel, doing smart
// batching. Once a batch is created, it gets proposed. Thus, we can reduce the number of
// times proposals happen, which is a great optimization to have (and a common one in our
// code base).
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
c := pb.NewZeroClient(pl.Get())
stream, err := c.Oracle(ctx, &api.Payload{})
if err != nil {
glog.Errorf("Error while calling Oracle %v\n", err)
time.Sleep(time.Second)
return
}
deltaCh := make(chan *pb.OracleDelta, 100)
go func() {
// This would exit when either a Recv() returns error. Or, cancel() is called by
// something outside of this goroutine.
defer func() {
if err := stream.CloseSend(); err != nil {
glog.Errorf("Error closing send stream: %+v", err)
}
}()
defer close(deltaCh)
for {
delta, err := stream.Recv()
if err != nil || delta == nil {
glog.Errorf("Error in oracle delta stream. Error: %v", err)
return
}
select {
case deltaCh <- delta:
case <-ctx.Done():
return
}
}
}()
for {
var delta *pb.OracleDelta
var batch int
select {
case delta = <-deltaCh:
if delta == nil {
return
}
batch++
case <-ticker.C:
newLead := g.Leader(0)
if newLead == nil || newLead.Addr != pl.Addr {
glog.Infof("Zero leadership changed. Renewing oracle delta stream.")
return
}
continue
case <-ctx.Done():
return
case <-g.closer.HasBeenClosed():
return
}
SLURP:
for {
select {
case more := <-deltaCh:
if more == nil {
return
}
batch++
delta.Txns = append(delta.Txns, more.Txns...)
delta.MaxAssigned = x.Max(delta.MaxAssigned, more.MaxAssigned)
default:
break SLURP
}
}
// Only the leader needs to propose the oracleDelta retrieved from Zero.
// The leader and the followers would not directly apply or use the
// oracleDelta streaming in from Zero. They would wait for the proposal to
// go through and be applied via node.Run. This saves us from many edge
// cases around network partitions and race conditions between prewrites and
// commits, etc.
if !g.Node.AmLeader() {
glog.Errorf("No longer the leader of group %d. Exiting", g.groupId())
return
}
// We should always sort the txns before applying. Otherwise, we might lose some of
// these updates, because we never write over a new version.
sort.Slice(delta.Txns, func(i, j int) bool {
return delta.Txns[i].CommitTs < delta.Txns[j].CommitTs
})
if len(delta.Txns) > 0 {
last := delta.Txns[len(delta.Txns)-1]
// Update MaxAssigned on commit so best effort queries can get back latest data.
delta.MaxAssigned = x.Max(delta.MaxAssigned, last.CommitTs)
}
if glog.V(3) {
glog.Infof("Batched %d updates. Max Assigned: %d. Proposing Deltas:",
batch, delta.MaxAssigned)
for _, txn := range delta.Txns {
if txn.CommitTs == 0 {
glog.Infof("Aborted: %d", txn.StartTs)
} else {
glog.Infof("Committed: %d -> %d", txn.StartTs, txn.CommitTs)
}
}
}
for {
// Block forever trying to propose this. Also this proposal should not be counted
// towards num pending proposals and be proposed right away.
err := g.Node.proposeAndWait(context.Background(), &pb.Proposal{Delta: delta})
if err == nil {
break
}
glog.Errorf("While proposing delta with MaxAssigned: %d and num txns: %d."+
" Error=%v. Retrying...\n", delta.MaxAssigned, len(delta.Txns), err)
}
}
}
for {
select {
case <-g.closer.HasBeenClosed():
return
case <-ticker.C:
// Only the leader needs to connect to Zero and get transaction
// updates.
if g.Node.AmLeader() {
blockingReceiveAndPropose()
}
}