More performant handling of out of order updates.

packages/firestore/src/remote/watch_change.ts

@@ -291,6 +291,7 @@ export class WatchChangeAggregator {
 
   /** Keeps track of the documents to update since the last raised snapshot. */
   private pendingDocumentUpdates = mutableDocumentMap();
+  private pendingDocumentUpdatesByTarget = documentTargetMap();
 
   /** A mapping of document keys to their set of target IDs. */
   private pendingDocumentTargetMapping = documentTargetMap();
@@ -587,16 +588,16 @@ export class WatchChangeAggregator {
         if (targetState.current && targetIsDocumentTarget(targetData.target)) {
           // Document queries for document that don't exist can produce an empty
           // result set. To update our local cache, we synthesize a document
-          // delete if we have not previously received the document. This
-          // resolves the limbo state of the document, removing it from
-          // limboDocumentRefs.
+          // delete if we have not previously received the document for this
+          // target. This resolves the limbo state of the document, removing it
+          // from limboDocumentRefs.
           //
           // TODO(dimond): Ideally we would have an explicit lookup target
           // instead resulting in an explicit delete message and we could
           // remove this special logic.
           const key = new DocumentKey(targetData.target.path);
           if (
-            this.pendingDocumentUpdates.get(key) === null &&
+            !this.ensureDocumentUpdateByTarget(key).has(targetId) &&
             !this.targetContainsDocument(targetId, key)
           ) {
             this.removeDocumentFromTarget(
@@ -655,6 +656,7 @@ export class WatchChangeAggregator {
     );
 
     this.pendingDocumentUpdates = mutableDocumentMap();
+    this.pendingDocumentUpdatesByTarget = documentTargetMap();
     this.pendingDocumentTargetMapping = documentTargetMap();
     this.pendingTargetResets = new SortedMap<TargetId, TargetPurpose>(
       primitiveComparator
@@ -680,10 +682,22 @@ export class WatchChangeAggregator {
     const targetState = this.ensureTargetState(targetId);
     targetState.addDocumentChange(document.key, changeType);
 
-    this.pendingDocumentUpdates = this.pendingDocumentUpdates.insert(
-      document.key,
-      document
-    );
+    const pendingDocumentUpdate = this.pendingDocumentUpdates.get(document.key);
+    if (
+      pendingDocumentUpdate === null ||
+      document.version.compareTo(pendingDocumentUpdate.version) > 0
+    ) {
+      this.pendingDocumentUpdates = this.pendingDocumentUpdates.insert(
+        document.key,
+        document
+      );
+    }
+
+    this.pendingDocumentUpdatesByTarget =
+      this.pendingDocumentUpdatesByTarget.insert(
+        document.key,
+        this.ensureDocumentUpdateByTarget(document.key).add(targetId)
+      );
 
     this.pendingDocumentTargetMapping =
       this.pendingDocumentTargetMapping.insert(
@@ -724,11 +738,23 @@ export class WatchChangeAggregator {
         this.ensureDocumentTargetMapping(key).delete(targetId)
       );
 
-    if (updatedDocument) {
-      this.pendingDocumentUpdates = this.pendingDocumentUpdates.insert(
+    this.pendingDocumentTargetMapping =
+      this.pendingDocumentTargetMapping.insert(
         key,
-        updatedDocument
+        this.ensureDocumentTargetMapping(key).add(targetId)
       );
+
+    if (updatedDocument) {
+      const pendingDocumentUpdate = this.pendingDocumentUpdates.get(key);
+      if (
+        pendingDocumentUpdate === null ||
+        updatedDocument.version.compareTo(pendingDocumentUpdate.version) > 0
+      ) {
+        this.pendingDocumentUpdates = this.pendingDocumentUpdates.insert(
+          key,
+          updatedDocument
+        );
+      }
     }
   }
 
@@ -782,6 +808,18 @@ export class WatchChangeAggregator {
     return targetMapping;
   }
 
+  private ensureDocumentUpdateByTarget(key: DocumentKey): SortedSet<TargetId> {
+    let targetMapping = this.pendingDocumentUpdatesByTarget.get(key);
+
+    if (!targetMapping) {
+      targetMapping = new SortedSet<TargetId>(primitiveComparator);
+      this.pendingDocumentUpdatesByTarget =
+        this.pendingDocumentUpdatesByTarget.insert(key, targetMapping);
+    }
+
+    return targetMapping;
+  }
+
   /**
    * Verifies that the user is still interested in this target (by calling
    * `getTargetDataForTarget()`) and that we are not waiting for pending ADDs

packages/firestore/test/unit/remote/remote_event.test.ts

@@ -323,7 +323,7 @@ describe('RemoteEvent', () => {
     const targets = listens(1, 2);
 
     const doc1a = doc('docs/1', 1, { value: 1 });
-    const doc1b = doc('docs/1', 1, { value: 2 });
+    const doc1b = doc('docs/1', 2, { value: 2 });
 
     const change1 = new DocumentWatchChange([1], [2], doc1a.key, doc1a);
     const change2 = new DocumentWatchChange([2], [1], doc1b.key, doc1b);