fix(proposals): Incremental proposal key for zero proposals (#8005)

Change the proposal's unique key to an atomic counter instead of using a randomly generated key.

(cherry picked from commit a515d0d)
(cherry picked from commit 2aa3d3e)

dgraph/cmd/zero/raft.go

@@ -18,13 +18,15 @@ package zero
 
 import (
 	"context"
+	"crypto/rand"
 	"encoding/binary"
 	"fmt"
 	"log"
 	"math"
 	"sort"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/dgraph-io/dgraph/conn"
@@ -47,6 +49,8 @@ const (
 	raftDefaults = "idx=1; learner=false;"
 )
 
+var proposalKey uint64
+
 type node struct {
 	*conn.Node
 	server *Server
@@ -80,8 +84,19 @@ func (n *node) AmLeader() bool {
 	return time.Since(n.lastQuorum) <= 5*time.Second
 }
 
+// {2 bytes Node ID} {4 bytes for random} {2 bytes zero}
+func (n *node) initProposalKey(id uint64) error {
+	x.AssertTrue(id != 0)
+	b := make([]byte, 8)
+	if _, err := rand.Read(b); err != nil {
+		return err
+	}
+	proposalKey = n.Id<<48 | binary.BigEndian.Uint64(b)<<16
+	return nil
+}
+
 func (n *node) uniqueKey() uint64 {
-	return uint64(n.Id)<<32 | uint64(n.Rand.Uint32())
+	return atomic.AddUint64(&proposalKey, 1)
 }
 
 var errInternalRetry = errors.New("Retry Raft proposal internally")
@@ -625,6 +640,7 @@ func (n *node) checkForCIDInEntries() (bool, error) {
 }
 
 func (n *node) initAndStartNode() error {
+	x.Check(n.initProposalKey(n.Id))
 	_, restart, err := n.PastLife()
 	x.Check(err)
 

worker/draft.go

@@ -1804,7 +1804,7 @@ func (n *node) retryUntilSuccess(fn func() error, pause time.Duration) {
 
 // InitAndStartNode gets called after having at least one membership sync with the cluster.
 func (n *node) InitAndStartNode() {
-	initProposalKey(n.Id)
+	x.Check(initProposalKey(n.Id))
 	_, restart, err := n.PastLife()
 	x.Check(err)
 

worker/proposal.go

@@ -18,6 +18,7 @@ package worker
 
 import (
 	"context"
+	"crypto/rand"
 	"encoding/binary"
 	"sync"
 	"sync/atomic"
@@ -27,7 +28,6 @@ import (
 	"github.com/dgraph-io/dgraph/protos/pb"
 	"github.com/dgraph-io/dgraph/schema"
 	"github.com/dgraph-io/dgraph/x"
-	"github.com/dgraph-io/ristretto/z"
 
 	ostats "go.opencensus.io/stats"
 	tag "go.opencensus.io/tag"
@@ -112,9 +112,14 @@ func (rl *rateLimiter) decr(retry int) {
 var proposalKey uint64
 
 // {2 bytes Node ID} {4 bytes for random} {2 bytes zero}
-func initProposalKey(id uint64) {
+func initProposalKey(id uint64) error {
 	x.AssertTrue(id != 0)
-	proposalKey = uint64(groups().Node.Id)<<48 | uint64(z.FastRand())<<16
+	b := make([]byte, 8)
+	if _, err := rand.Read(b); err != nil {
+		return err
+	}
+	proposalKey = groups().Node.Id<<48 | binary.BigEndian.Uint64(b)<<16
+	return nil
 }
 
 // uniqueKey is meant to be unique across all the replicas.