move index check

db/collection_index.go

@@ -197,9 +197,13 @@ func (c *collection) updateIndexedDoc(
 		return err
 	}
 	for _, index := range c.indexes {
-		err = index.Update(ctx, txn, oldDoc, doc)
-		if err != nil {
-			return err
+		// We only need to update the index if one of the indexed fields
+		// on the document has been changed.
+		if isUpdatingIndexedFields(index, doc) {
+			err = index.Update(ctx, txn, oldDoc, doc)
+			if err != nil {
+				return err
+			}
 		}
 	}
 	return nil
@@ -588,3 +592,18 @@ func generateIndexName(col client.Collection, fields []client.IndexedFieldDescri
 	}
 	return sb.String()
 }
+
+func isUpdatingIndexedFields(index CollectionIndex, doc *client.Document) bool {
+	for _, docField := range doc.Fields() {
+		// It is safe to discard the error here for simplicity.
+		val, _ := doc.GetValueWithField(docField)
+		if val.IsDirty() {
+			for _, indexedFields := range index.Description().Fields {
+				if indexedFields.Name == docField.Name() {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}

db/index.go

@@ -11,7 +11,6 @@
 package db
 
 import (
-	"bytes"
 	"context"
 	"time"
 
@@ -363,15 +362,6 @@ func (index *collectionUniqueIndex) prepareIndexRecordToStore(
 			return core.IndexDataStoreKey{}, nil, err
 		}
 		if exists {
-			if oldDoc != nil {
-				oldKey, oldVal, err := index.getDocumentsIndexRecord(oldDoc)
-				if err != nil {
-					return core.IndexDataStoreKey{}, nil, err
-				}
-				if oldKey.ToString() == key.ToString() && bytes.Equal(oldVal, val) {
-					return core.IndexDataStoreKey{}, nil, nil
-				}
-			}
 			return core.IndexDataStoreKey{}, nil, index.newUniqueIndexError(doc)
 		}
 	}
@@ -396,11 +386,6 @@ func (index *collectionUniqueIndex) Update(
 	if err != nil {
 		return err
 	}
-	if newKey.ToString() == "" {
-		// This will happen when the updated doc results in the same key-value pair.
-		// The outcome is a no-op.
-		return nil
-	}
 	err = index.deleteDocIndex(ctx, txn, oldDoc)
 	if err != nil {
 		return err