added optimization

raft/raft.go

@@ -240,6 +240,9 @@ type AppendEntriesArgs struct {
 type AppendEntriesReply struct {
     Term int // current term (for leader to update itself)
     Success bool // true if follower contained entry matching prevLogIndex and prevLogTerm
+
+    ConflictTerm int // term of conflicting entry
+    ConflictIndex int // index of first entry in log that conflicts with new entries
 }
 
 // AppendEntries RPC handler
@@ -252,7 +255,11 @@ func (rf *Raft) AppendEntries(args *AppendEntriesArgs, reply *AppendEntriesReply
     defer rf.mu.Unlock()
 
     rf.resetElectionTimer()
+
+    reply.Term = rf.currentTerm
     reply.Success = false
+    reply.ConflictTerm = -1
+    reply.ConflictIndex = -1
 
     // candidate term is less than current term
     if args.Term < rf.currentTerm {
@@ -274,6 +281,23 @@ func (rf *Raft) AppendEntries(args *AppendEntriesArgs, reply *AppendEntriesReply
         return
     }
 
+    // check if log contains entry within log
+    if args.PrevLogIndex >= len(rf.log) {
+        reply.ConflictIndex = len(rf.log)
+        return
+    }
+
+    // check if log entry at precLogIndex does not match prevLogTerm
+    if rf.log[args.PrevLogIndex].Term != args.PrevLogTerm {
+        reply.ConflictTerm = rf.log[args.PrevLogIndex].Term
+        conflictIndex := args.PrevLogIndex
+        for conflictIndex >= 0 && rf.log[conflictIndex].Term == reply.ConflictTerm {
+            conflictIndex--
+        }
+        reply.ConflictIndex = conflictIndex + 1
+        return
+    }
+
     // // check if existing entry conflicts with new entries
     // // delete any conflicting entries
     // for j, entry := range args.Entries {
@@ -318,7 +342,6 @@ func (rf *Raft) AppendEntries(args *AppendEntriesArgs, reply *AppendEntriesReply
         }
     }
 	
-    reply.Term = rf.currentTerm
     reply.Success = true
 
     // fmt.Println(rf.me, rf.log)
@@ -425,8 +448,31 @@ func (rf *Raft) sendHeartbeats() {
                         rf.matchIndex[server] = newMatchIndex
                         rf.nextIndex[server] = newMatchIndex + 1
                     } else {
-                        if rf.nextIndex[server] > 1 {
-                            rf.nextIndex[server]--
+                        // if rf.nextIndex[server] > 1 {
+                        //     rf.nextIndex[server]--
+                        // }
+
+                        // optimized nextIndex calculation
+                        if reply.ConflictTerm != -1 {
+                            conflictTerm := reply.ConflictTerm
+                            lastIndexOfTerm := -1
+                            for i := len(rf.log) - 1; i >= 0; i-- {
+                                if rf.log[i].Term == conflictTerm {
+                                    lastIndexOfTerm = i
+                                    break
+                                }
+                            }
+                            if lastIndexOfTerm >= 0 {
+                                rf.nextIndex[server] = lastIndexOfTerm + 1
+                            } else {
+                                rf.nextIndex[server] = reply.ConflictIndex
+                            }
+                        } else {
+                            rf.nextIndex[server] = reply.ConflictIndex
+                        }
+
+                        if rf.nextIndex[server] < 1 {
+                            rf.nextIndex[server] = 1
                         }
                     }