perf(metarepos): add a pool for *mrpb.RaftEntry (#536)

### What this PR does

This change adds the pool for *mrpb.RaftEntry to reuse it.

internal/metarepos/raft_metadata_repository.go

@@ -302,15 +302,16 @@ Loop:
 			b, err := e.Marshal()
 			if err != nil {
 				mr.logger.Error(err.Error())
+				e.Release()
 				continue
 			}
-			// Release *mrpb.Reports only if e contains Reports.
-			e.GetRequest().Report.Release()
+			nodeIndex, requestIndex := e.NodeIndex, e.RequestIndex
+			e.Release()
 
 			select {
 			case mr.rnProposeC <- b:
 			case <-ctx.Done():
-				mr.sendAck(e.NodeIndex, e.RequestIndex, ctx.Err())
+				mr.sendAck(nodeIndex, requestIndex, ctx.Err())
 			}
 		case <-ctx.Done():
 			break Loop
@@ -1150,53 +1151,69 @@ func (mr *RaftMetadataRepository) proposeReport(snID types.StorageNodeID, ur []s
 	return nil
 }
 
-func (mr *RaftMetadataRepository) propose(ctx context.Context, r interface{}, guarantee bool) error {
-	e := &mrpb.RaftEntry{}
-	e.Request.SetValue(r)
-	e.NodeIndex = uint64(mr.nodeID)
-	e.RequestIndex = UnusedRequestIndex
+func (mr *RaftMetadataRepository) leaseRaftEntry(request any, requestIndex uint64) *mrpb.RaftEntry {
+	re := mrpb.NewRaftEntry()
+	re.Request.SetValue(request)
+	re.NodeIndex = uint64(mr.nodeID)
+	re.RequestIndex = requestIndex
+	return re
+}
 
-	if guarantee {
-		c := make(chan error, 1)
-		rIdx := mr.requestNum.Add(1)
+func (mr *RaftMetadataRepository) proposeWithoutGuarantee(ctx context.Context, request any) (err error) {
+	re := mr.leaseRaftEntry(request, UnusedRequestIndex)
+	select {
+	case mr.proposeC <- re:
+		return nil
+	case <-ctx.Done():
+		err = ctx.Err()
+	default:
+		err = verrors.ErrIgnore
+	}
+	if err != nil {
+		re.Release()
+	}
+	return err
+}
 
-		e.RequestIndex = rIdx
-		mr.requestMap.Store(rIdx, c)
-		defer mr.requestMap.Delete(rIdx)
+func (mr *RaftMetadataRepository) proposeWithGuarantee(ctx context.Context, request any) error {
+	rIdx := mr.requestNum.Add(1)
+	c := make(chan error, 1)
+	mr.requestMap.Store(rIdx, c)
+	defer mr.requestMap.Delete(rIdx)
 
-		t := time.NewTimer(mr.raftProposeTimeout)
-		defer t.Stop()
+	t := time.NewTimer(mr.raftProposeTimeout)
+	defer t.Stop()
 
-	PROPOSE:
-		select {
-		case mr.proposeC <- e:
-		case <-t.C:
-			t.Reset(mr.raftProposeTimeout)
-			goto PROPOSE
-		case <-ctx.Done():
-			return ctx.Err()
-		}
+	re := mr.leaseRaftEntry(request, rIdx)
 
-		select {
-		case err := <-c:
-			return err
-		case <-t.C:
-			t.Reset(mr.raftProposeTimeout)
-			goto PROPOSE
-		case <-ctx.Done():
-			return ctx.Err()
-		}
-	} else {
-		select {
-		case <-ctx.Done():
-			return ctx.Err()
-		case mr.proposeC <- e:
-		default:
-			return verrors.ErrIgnore
-		}
+Propose:
+	select {
+	case mr.proposeC <- re:
+	case <-t.C:
+		t.Reset(mr.raftProposeTimeout)
+		goto Propose
+	case <-ctx.Done():
+		re.Release()
+		return ctx.Err()
 	}
 
-	return nil
+	select {
+	case err := <-c:
+		return err
+	case <-t.C:
+		t.Reset(mr.raftProposeTimeout)
+		re = mr.leaseRaftEntry(request, rIdx)
+		goto Propose
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
+func (mr *RaftMetadataRepository) propose(ctx context.Context, request interface{}, guarantee bool) error {
+	if !guarantee {
+		return mr.proposeWithoutGuarantee(ctx, request)
+	}
+	return mr.proposeWithGuarantee(ctx, request)
 }
 
 func (mr *RaftMetadataRepository) proposeConfChange(ctx context.Context, r raftpb.ConfChange) error {

proto/mrpb/raft_entry.go

@@ -53,3 +53,21 @@ func (rq *ReportQueue) Release() {
 		reportQueuePool.Put(rq)
 	}
 }
+
+var raftEntryPool = sync.Pool{
+	New: func() any {
+		return &RaftEntry{}
+	},
+}
+
+func NewRaftEntry() *RaftEntry {
+	return raftEntryPool.Get().(*RaftEntry)
+}
+
+func (re *RaftEntry) Release() {
+	if re != nil {
+		re.Request.Report.Release()
+		re.Reset()
+		raftEntryPool.Put(re)
+	}
+}