firestore: Improve query performance by avoiding excessive Comparator instance creation (#7388)

Author: dconeybe

firebase-firestore/CHANGELOG.md

@@ -10,6 +10,8 @@
   [#7376](//github.com/firebase/firebase-android-sdk/issues/7376)
 - [changed] Improve query performance via internal memoization of calculated document data.
   [#7370](//github.com/firebase/firebase-android-sdk/issues/7370)
+- [changed] Improve query performance by avoiding excessive Comparator instance creation.
+  [#7388](//github.com/firebase/firebase-android-sdk/pull/7388)
 
 # 26.0.0
 

firebase-firestore/src/main/java/com/google/firebase/firestore/core/View.java

@@ -29,6 +29,7 @@
 import com.google.firebase.firestore.remote.TargetChange;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
 
@@ -156,6 +157,7 @@ public DocumentChanges computeDocChanges(
             ? oldDocumentSet.getFirstDocument()
             : null;
 
+    Comparator<Document> queryComparator = query.comparator();
     for (Map.Entry<DocumentKey, Document> entry : docChanges) {
       DocumentKey key = entry.getKey();
       Document oldDoc = oldDocumentSet.getDocument(key);
@@ -182,9 +184,9 @@ public DocumentChanges computeDocChanges(
             changeSet.addChange(DocumentViewChange.create(Type.MODIFIED, newDoc));
             changeApplied = true;
 
-            if ((lastDocInLimit != null && query.comparator().compare(newDoc, lastDocInLimit) > 0)
+            if ((lastDocInLimit != null && queryComparator.compare(newDoc, lastDocInLimit) > 0)
                 || (firstDocInLimit != null
-                    && query.comparator().compare(newDoc, firstDocInLimit) < 0)) {
+                    && queryComparator.compare(newDoc, firstDocInLimit) < 0)) {
               // This doc moved from inside the limit to outside the limit. That means there may be
               // some doc in the local cache that should be included instead.
               needsRefill = true;
@@ -296,15 +298,17 @@ public ViewChange applyChanges(
     mutatedKeys = docChanges.mutatedKeys;
 
     // Sort changes based on type and query comparator.
+
     List<DocumentViewChange> viewChanges = docChanges.changeSet.getChanges();
+    Comparator<Document> queryComparator = query.comparator();
     Collections.sort(
         viewChanges,
         (DocumentViewChange o1, DocumentViewChange o2) -> {
           int typeComp = Integer.compare(View.changeTypeOrder(o1), View.changeTypeOrder(o2));
           if (typeComp != 0) {
             return typeComp;
           }
-          return query.comparator().compare(o1.getDocument(), o2.getDocument());
+          return queryComparator.compare(o1.getDocument(), o2.getDocument());
         });
     applyTargetChange(targetChange);
     List<LimboDocumentChange> limboDocumentChanges =