Improve Version Vector Handling for Legacy SDK and Snapshots

packages/sdk/src/document/change/change_id.ts

@@ -85,8 +85,17 @@ export class ChangeID {
   public syncClocks(other: ChangeID): ChangeID {
     const lamport =
       other.lamport > this.lamport ? other.lamport + 1n : this.lamport + 1n;
-    const maxVersionVector = this.versionVector.max(other.versionVector);
 
+    // NOTE(chacha912): For changes created by legacy SDK prior to v0.5.2 that lack version
+    // vectors, document's version vector was not being properly accumlated. To address this,
+    // we generate a version vector using the lamport timestamp when no version vector exists.
+    let otherVV = other.versionVector;
+    if (otherVV.size() === 0) {
+      otherVV = otherVV.deepcopy();
+      otherVV.set(other.actor, other.lamport);
+    }
+
+    const maxVersionVector = this.versionVector.max(otherVV);
     const newID = new ChangeID(
       this.clientSeq,
       lamport,
@@ -103,7 +112,17 @@ export class ChangeID {
    */
   public setClocks(otherLamport: bigint, vector: VersionVector): ChangeID {
     const lamport =
-      otherLamport > this.lamport ? otherLamport : this.lamport + 1n;
+      otherLamport > this.lamport ? otherLamport + 1n : this.lamport + 1n;
+
+    // NOTE(chacha912): Documents created by server may have an InitialActorID
+    // in their version vector. Although server is not an actual client, it
+    // generates document snapshots from changes by participating with an
+    // InitialActorID during document instance creation and accumulating stored
+    // changes in DB.
+    // Semantically, including a non-client actor in version vector is
+    // problematic. To address this, we remove the InitialActorID from snapshots.
+    vector.unset(InitialActorID);
+
     const maxVersionVector = this.versionVector.max(vector);
     maxVersionVector.set(this.actor, lamport);
 

packages/sdk/src/document/document.ts

@@ -1450,7 +1450,10 @@ export class Document<T, P extends Indexable = Indexable> {
     const { root, presences } = converter.bytesToSnapshot<P>(snapshot);
     this.root = new CRDTRoot(root);
     this.presences = presences;
-    this.changeID = this.changeID.setClocks(serverSeq, snapshotVector);
+    this.changeID = this.changeID.setClocks(
+      snapshotVector.maxLamport(),
+      snapshotVector,
+    );
 
     // drop clone because it is contaminated.
     this.clone = undefined;

packages/sdk/src/document/time/version_vector.ts

@@ -36,6 +36,13 @@ export class VersionVector {
     this.vector.set(actorID, lamport);
   }
 
+  /**
+   * `unset` removes the version for the given actor from the VersionVector.
+   */
+  public unset(actorID: string): void {
+    this.vector.delete(actorID);
+  }
+
   /**
    * `get` gets the lamport timestamp of the given actor.
    */

packages/sdk/test/integration/gc_test.ts

@@ -4,7 +4,11 @@ import {
   testRPCAddr,
   toDocKey,
 } from '@yorkie-js-sdk/test/integration/integration_helper';
-import { MaxVersionVector, versionVectorHelper } from '../helper/helper';
+import {
+  MaxVersionVector,
+  versionVectorHelper,
+  DefaultSnapshotThreshold,
+} from '../helper/helper';
 
 describe('Garbage Collection', function () {
   it('getGarbageLen should return the actual number of elements garbage-collected', async function ({
@@ -1701,7 +1705,7 @@ describe('Garbage Collection', function () {
     task,
   }) {
     type TestDoc = { t: Text };
-    const docKey = toDocKey(`${task.name}-${new Date().getTime()}`);
+    const docKey = toDocKey(`${new Date().getTime()}-${task.name}`);
     const doc1 = new yorkie.Document<TestDoc>(docKey);
     const doc2 = new yorkie.Document<TestDoc>(docKey);
     const client1 = new yorkie.Client(testRPCAddr);
@@ -1875,7 +1879,7 @@ describe('Garbage Collection', function () {
     task,
   }) {
     type TestDoc = { t: Text };
-    const docKey = toDocKey(`${task.name}-${new Date().getTime()}`);
+    const docKey = toDocKey(`${new Date().getTime()}-${task.name}`);
     const doc1 = new yorkie.Document<TestDoc>(docKey);
     const doc2 = new yorkie.Document<TestDoc>(docKey);
     const client1 = new yorkie.Client(testRPCAddr);
@@ -2226,4 +2230,129 @@ describe('Garbage Collection', function () {
     await client2.deactivate();
     await client3.deactivate();
   });
+
+  it('snapshot version vector test', async function ({ task }) {
+    type TestDoc = { t: Text };
+    const docKey = toDocKey(`${task.name}-${new Date().getTime()}`);
+    const doc1 = new yorkie.Document<TestDoc>(docKey);
+    const doc2 = new yorkie.Document<TestDoc>(docKey);
+    const doc3 = new yorkie.Document<TestDoc>(docKey);
+    const client1 = new yorkie.Client(testRPCAddr);
+    const client2 = new yorkie.Client(testRPCAddr);
+    const client3 = new yorkie.Client(testRPCAddr);
+    await client1.activate();
+    await client2.activate();
+    await client3.activate();
+
+    await client1.attach(doc1, { syncMode: SyncMode.Manual });
+    await client2.attach(doc2, { syncMode: SyncMode.Manual });
+    await client3.attach(doc3, { syncMode: SyncMode.Manual });
+
+    doc1.update((root) => {
+      root.t = new Text();
+      root.t.edit(0, 0, 'a');
+    }, 'sets text');
+
+    await client1.sync();
+    await client2.sync();
+    await client3.sync();
+
+    assert.equal(
+      versionVectorHelper(doc1.getVersionVector(), [
+        { actor: client1.getID()!, lamport: BigInt(4) },
+        { actor: client2.getID()!, lamport: BigInt(1) },
+        { actor: client3.getID()!, lamport: BigInt(1) },
+      ]),
+      true,
+    );
+    assert.equal(
+      versionVectorHelper(doc2.getVersionVector(), [
+        { actor: client1.getID()!, lamport: BigInt(2) },
+        { actor: client2.getID()!, lamport: BigInt(4) },
+        { actor: client3.getID()!, lamport: BigInt(1) },
+      ]),
+      true,
+    );
+    assert.equal(
+      versionVectorHelper(doc3.getVersionVector(), [
+        { actor: client1.getID()!, lamport: BigInt(2) },
+        { actor: client2.getID()!, lamport: BigInt(1) },
+        { actor: client3.getID()!, lamport: BigInt(4) },
+      ]),
+      true,
+    );
+
+    // 01. Updates changes over snapshot threshold.
+    for (let idx = 0; idx < DefaultSnapshotThreshold / 2; idx++) {
+      doc1.update((root) => {
+        root.t.edit(0, 0, `${idx % 10}`);
+      });
+      await client1.sync();
+      await client2.sync();
+
+      doc2.update((root) => {
+        root.t.edit(0, 0, `${idx % 10}`);
+      });
+      await client2.sync();
+      await client1.sync();
+    }
+
+    assert.equal(
+      versionVectorHelper(doc1.getVersionVector(), [
+        { actor: client1.getID()!, lamport: BigInt(2004) },
+        { actor: client2.getID()!, lamport: BigInt(2003) },
+        { actor: client3.getID()!, lamport: BigInt(1) },
+      ]),
+      true,
+    );
+    assert.equal(
+      versionVectorHelper(doc2.getVersionVector(), [
+        { actor: client1.getID()!, lamport: BigInt(2001) },
+        { actor: client2.getID()!, lamport: BigInt(2003) },
+        { actor: client3.getID()!, lamport: BigInt(1) },
+      ]),
+      true,
+    );
+    assert.equal(
+      versionVectorHelper(doc3.getVersionVector(), [
+        { actor: client1.getID()!, lamport: BigInt(2) },
+        { actor: client2.getID()!, lamport: BigInt(1) },
+        { actor: client3.getID()!, lamport: BigInt(4) },
+      ]),
+      true,
+    );
+
+    // 02. Makes local changes then pull a snapshot from the server.
+    doc3.update((root) => {
+      root.t.edit(0, 0, 'c');
+    });
+    await client3.sync();
+    assert.equal(
+      versionVectorHelper(doc3.getVersionVector(), [
+        { actor: client1.getID()!, lamport: BigInt(2001) },
+        { actor: client2.getID()!, lamport: BigInt(2003) },
+        { actor: client3.getID()!, lamport: BigInt(2006) },
+      ]),
+      true,
+    );
+    assert.equal(
+      DefaultSnapshotThreshold + 2,
+      doc3.getRoot().t.toString().length,
+    );
+
+    // 03. Delete text after receiving the snapshot.
+    doc3.update((root) => {
+      root.t.edit(1, 3, '');
+    });
+    assert.equal(DefaultSnapshotThreshold, doc3.getRoot().t.toString().length);
+    await client3.sync();
+    await client2.sync();
+    await client1.sync();
+    assert.equal(DefaultSnapshotThreshold, doc2.getRoot().t.toString().length);
+    assert.equal(DefaultSnapshotThreshold, doc1.getRoot().t.toString().length);
+
+    await client1.deactivate();
+    await client2.deactivate();
+    await client3.deactivate();
+  }, 50000);
 });