Optimize max VersionVector in ApplyChanges to improve memory efficiency

api/converter/from_pb.go

@@ -154,12 +154,12 @@ func FromChanges(pbChanges []*api.Change) ([]*change.Change, error) {
 func fromChangeID(id *api.ChangeID) (change.ID, error) {
 	actorID, err := time.ActorIDFromBytes(id.ActorId)
 	if err != nil {
-		return change.InitialID, err
+		return change.InitialID(), err
 	}
 
 	vector, err := FromVersionVector(id.VersionVector)
 	if err != nil {
-		return change.InitialID, err
+		return change.InitialID(), err
 	}
 
 	return change.NewID(

pkg/document/change/id.go

@@ -25,12 +25,6 @@ const (
 	InitialLamport = 0
 )
 
-var (
-	// InitialID represents the initial state ID. Usually this is used to
-	// represent a state where nothing has been edited.
-	InitialID = NewID(InitialClientSeq, InitialServerSeq, InitialLamport, time.InitialActorID, time.InitialVersionVector)
-)
-
 // ID represents the identifier of the change. It is used to identify the
 // change and to order the changes. It is also used to detect the relationship
 // between changes whether they are causally related or concurrent.
@@ -75,6 +69,12 @@ func NewID(
 	}
 }
 
+// InitialID creates an initial state ID. Usually this is used to
+// represent a state where nothing has been edited.
+func InitialID() ID {
+	return NewID(InitialClientSeq, InitialServerSeq, InitialLamport, time.InitialActorID, time.NewVersionVector())
+}
+
 // Next creates a next ID of this ID.
 func (id ID) Next() ID {
 	versionVector := id.versionVector.DeepCopy()
@@ -113,7 +113,7 @@ func (id ID) SyncClocks(other ID) ID {
 		otherVV.Set(other.actorID, other.lamport)
 	}
 
-	newID := NewID(id.clientSeq, InitialServerSeq, lamport, id.actorID, id.versionVector.Max(otherVV))
+	newID := NewID(id.clientSeq, InitialServerSeq, lamport, id.actorID, id.versionVector.Max(&otherVV))
 	newID.versionVector.Set(id.actorID, lamport)
 	return newID
 }
@@ -135,7 +135,7 @@ func (id ID) SetClocks(otherLamport int64, vector time.VersionVector) ID {
 	// problematic. To address this, we remove the InitialActorID from snapshots.
 	vector.Unset(time.InitialActorID)
 
-	newID := NewID(id.clientSeq, id.serverSeq, lamport, id.actorID, id.versionVector.Max(vector))
+	newID := NewID(id.clientSeq, id.serverSeq, lamport, id.actorID, id.versionVector.Max(&vector))
 	newID.versionVector.Set(id.actorID, lamport)
 
 	return newID

pkg/document/internal_document.go

@@ -97,7 +97,7 @@ func NewInternalDocument(k key.Key) *InternalDocument {
 		status:        StatusDetached,
 		root:          crdt.NewRoot(root),
 		checkpoint:    change.InitialCheckpoint,
-		changeID:      change.InitialID,
+		changeID:      change.InitialID(),
 		presences:     innerpresence.NewMap(),
 		onlineClients: &gosync.Map{},
 	}
@@ -116,14 +116,17 @@ func NewInternalDocumentFromSnapshot(
 		return nil, err
 	}
 
+	changeID := change.InitialID()
+	changeID.SetClocks(lamport, vector)
+
 	return &InternalDocument{
 		key:           k,
 		status:        StatusDetached,
 		root:          crdt.NewRoot(obj),
 		presences:     presences,
 		onlineClients: &gosync.Map{},
 		checkpoint:    change.InitialCheckpoint.NextServerSeq(serverSeq),
-		changeID:      change.InitialID.SetClocks(lamport, vector),
+		changeID:      changeID,
 	}, nil
 }
 

pkg/document/time/version_vector.go

@@ -130,54 +130,62 @@ func (v VersionVector) EqualToOrAfter(other *Ticket) bool {
 	return clientLamport >= other.lamport
 }
 
-// Min returns new vv consists of every min value in each column.
-func (v VersionVector) Min(other VersionVector) VersionVector {
-	minVV := NewVersionVector()
+// Min modifies the receiver in-place to contain the minimum values between itself
+// and the given version vector, and returns the modified receiver.
+// Note: This method modifies the receiver for memory efficiency.
+func (v VersionVector) Min(other *VersionVector) VersionVector {
+	if other == nil {
+		return v
+	}
 
 	for key, value := range v {
-		if otherValue, exists := other[key]; exists {
+		if otherValue, exists := (*other)[key]; exists {
 			if value < otherValue {
-				minVV[key] = value
+				v[key] = value
 			} else {
-				minVV[key] = otherValue
+				v[key] = otherValue
 			}
 		} else {
-			minVV[key] = 0
+			v[key] = 0
 		}
 	}
 
-	for key := range other {
+	for key := range *other {
 		if _, exists := v[key]; !exists {
-			minVV[key] = 0
+			v[key] = 0
 		}
 	}
 
-	return minVV
+	return v
 }
 
-// Max returns new vv consists of every max value in each column.
-func (v VersionVector) Max(other VersionVector) VersionVector {
-	maxVV := NewVersionVector()
+// Max modifies the receiver in-place to contain the maximum values between itself
+// and the given version vector, and returns the modified receiver.
+// Note: This method modifies the receiver for memory efficiency.
+func (v VersionVector) Max(other *VersionVector) VersionVector {
+	if other == nil {
+		return v
+	}
 
 	for key, value := range v {
-		if otherValue, exists := other[key]; exists {
+		if otherValue, exists := (*other)[key]; exists {
 			if value > otherValue {
-				maxVV[key] = value
+				v[key] = value
 			} else {
-				maxVV[key] = otherValue
+				v[key] = otherValue
 			}
 		} else {
-			maxVV[key] = value
+			v[key] = value
 		}
 	}
 
-	for key, value := range other {
+	for key, value := range *other {
 		if _, exists := v[key]; !exists {
-			maxVV[key] = value
+			v[key] = value
 		}
 	}
 
-	return maxVV
+	return v
 }
 
 // MaxLamport returns max lamport value in version vector.

pkg/document/time/version_vector_test.go

@@ -99,9 +99,9 @@ func TestVersionVector(t *testing.T) {
 		},
 	}
 
-	for _, tc := range tests {
+	for i, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {
-			result := tc.v1.Min(tc.v2)
+			result := tc.v1.Min(&tests[i].v2)
 			assert.Equal(t, tc.expect, result)
 		})
 	}

server/backend/database/memory/database.go

@@ -1372,7 +1372,7 @@ func (d *DB) UpdateAndFindMinSyncedVersionVector(
 	if minVersionVector == nil {
 		minVersionVector = versionVector
 	} else {
-		minVersionVector = minVersionVector.Min(versionVector)
+		minVersionVector = minVersionVector.Min(&versionVector)
 	}
 
 	// 03. Update current client's version vector. If the client is detached, remove it.

server/backend/database/mongo/client.go

@@ -1264,7 +1264,7 @@ func (c *Client) UpdateAndFindMinSyncedVersionVector(
 	if minVersionVector == nil {
 		minVersionVector = versionVector
 	} else {
-		minVersionVector = minVersionVector.Min(versionVector)
+		minVersionVector = minVersionVector.Min(&versionVector)
 	}
 
 	// 03. Update current client's version vector. If the client is detached, remove it.

test/helper/helper.go

@@ -117,7 +117,7 @@ func TestRoot() *crdt.Root {
 // TextChangeContext returns the context of test change.
 func TextChangeContext(root *crdt.Root) *change.Context {
 	return change.NewContext(
-		change.InitialID,
+		change.InitialID(),
 		"",
 		root,
 	)