add configurable min documents to create indexes

Author: cherylEnkidu

firebase-firestore/src/main/java/com/google/firebase/firestore/local/QueryEngine.java

@@ -16,6 +16,7 @@
 
 import static com.google.firebase.firestore.util.Assert.hardAssert;
 
+import androidx.annotation.VisibleForTesting;
 import com.google.firebase.database.collection.ImmutableSortedMap;
 import com.google.firebase.database.collection.ImmutableSortedSet;
 import com.google.firebase.firestore.core.Query;
@@ -60,13 +61,17 @@
  */
 public class QueryEngine {
   private static final String LOG_TAG = "QueryEngine";
+  private static final int MIN_COLLECTION_SIZE_TO_AUTO_CREATE_INDEX = 100;
 
   private LocalDocumentsView localDocumentsView;
   private IndexManager indexManager;
   private boolean initialized;
 
   private boolean automaticIndexingEnabled = false;
 
+  /** SDK only decides whether it should create index when collection size is larger than this. */
+  private int minCollectionSizeToAutoCreateIndex = MIN_COLLECTION_SIZE_TO_AUTO_CREATE_INDEX;
+
   public void initialize(LocalDocumentsView localDocumentsView, IndexManager indexManager) {
     this.localDocumentsView = localDocumentsView;
     this.indexManager = indexManager;
@@ -111,6 +116,15 @@ public ImmutableSortedMap<DocumentKey, Document> getDocumentsMatchingQuery(
    */
   // TODO(csi): Auto experiment data.
   private void CreateCacheIndexes(Query query, QueryContext context, int resultSize) {
+    if (context.getDocumentReadCount() < minCollectionSizeToAutoCreateIndex) {
+      Logger.debug(
+          LOG_TAG,
+          "SDK will only creates cache indexes for collection contains more than or equal to "
+              + "%s documents.",
+          minCollectionSizeToAutoCreateIndex);
+      return;
+    }
+
     String decisionStr = "";
     // If evaluation is updated, please update tests in SQLiteLocalStoreTest.java
     if (context.getDocumentReadCount() > 2 * resultSize) {
@@ -305,4 +319,9 @@ private ImmutableSortedMap<DocumentKey, Document> appendRemainingResults(
     }
     return remainingResults;
   }
+
+  @VisibleForTesting
+  void setMinCollectionSizeToAutoCreateIndex(int newMin) {
+    minCollectionSizeToAutoCreateIndex = newMin;
+  }
 }

firebase-firestore/src/test/java/com/google/firebase/firestore/local/CountingQueryEngine.java

@@ -97,6 +97,11 @@ public void disableIndexAutoCreation() {
     queryEngine.disableIndexAutoCreation();
   }
 
+  @Override
+  public void setMinCollectionSizeToAutoCreateIndex(int newMin) {
+    queryEngine.setMinCollectionSizeToAutoCreateIndex(newMin);
+  }
+
   /**
    * Returns the number of documents returned by the RemoteDocumentCache's `getAll()` API (since the
    * last call to `resetCounts()`)

firebase-firestore/src/test/java/com/google/firebase/firestore/local/LocalStoreTestCase.java

@@ -232,6 +232,10 @@ protected void disableIndexAutoCreation() {
     queryEngine.disableIndexAutoCreation();
   }
 
+  protected void setMinCollectionSizeToAutoCreateIndex(int newMin) {
+    queryEngine.setMinCollectionSizeToAutoCreateIndex(newMin);
+  }
+
   private void releaseTarget(int targetId) {
     localStore.releaseTarget(targetId);
   }

firebase-firestore/src/test/java/com/google/firebase/firestore/local/SQLiteLocalStoreTest.java

@@ -373,6 +373,7 @@ public void testIndexAutoCreationWorks() {
     int targetId = allocateQuery(query);
 
     enableIndexAutoCreation();
+    setMinCollectionSizeToAutoCreateIndex(0);
 
     applyRemoteEvent(addedRemoteEvent(doc("coll/a", 10, map("matches", true)), targetId));
     applyRemoteEvent(addedRemoteEvent(doc("coll/b", 10, map("matches", false)), targetId));
@@ -396,12 +397,40 @@ public void testIndexAutoCreationWorks() {
     assertQueryReturned("coll/a", "coll/e", "coll/f");
   }
 
+  @Test
+  public void testIndexAutoCreationDoesNotWorkWhenCollectionSizeIsTooSmall() {
+    Query query = query("coll").filter(filter("matches", "==", true));
+    int targetId = allocateQuery(query);
+
+    enableIndexAutoCreation();
+
+    applyRemoteEvent(addedRemoteEvent(doc("coll/a", 10, map("matches", true)), targetId));
+    applyRemoteEvent(addedRemoteEvent(doc("coll/b", 10, map("matches", false)), targetId));
+    applyRemoteEvent(addedRemoteEvent(doc("coll/c", 10, map("matches", false)), targetId));
+    applyRemoteEvent(addedRemoteEvent(doc("coll/d", 10, map("matches", false)), targetId));
+    applyRemoteEvent(addedRemoteEvent(doc("coll/e", 10, map("matches", true)), targetId));
+
+    // SDK will not create indexes since collection size is too small.
+    executeQuery(query);
+    assertRemoteDocumentsRead(/* byKey= */ 0, /* byCollection= */ 2);
+    assertQueryReturned("coll/a", "coll/e");
+
+    backfillIndexes();
+
+    applyRemoteEvent(addedRemoteEvent(doc("coll/f", 20, map("matches", true)), targetId));
+
+    executeQuery(query);
+    assertRemoteDocumentsRead(/* byKey= */ 0, /* byCollection= */ 3);
+    assertQueryReturned("coll/a", "coll/e", "coll/f");
+  }
+
   @Test
   public void testIndexAutoCreationWorksWhenBackfillerRunsHalfway() {
     Query query = query("coll").filter(filter("matches", "==", true));
     int targetId = allocateQuery(query);
 
     enableIndexAutoCreation();
+    setMinCollectionSizeToAutoCreateIndex(0);
 
     applyRemoteEvent(addedRemoteEvent(doc("coll/a", 10, map("matches", true)), targetId));
     applyRemoteEvent(addedRemoteEvent(doc("coll/b", 10, map("matches", false)), targetId));
@@ -433,6 +462,7 @@ public void testIndexCreatedByIndexAutoCreationExistsAfterTurnOffAutoCreation()
     int targetId = allocateQuery(query);
 
     enableIndexAutoCreation();
+    setMinCollectionSizeToAutoCreateIndex(0);
 
     applyRemoteEvent(addedRemoteEvent(doc("coll/a", 10, map("matches", true)), targetId));
     applyRemoteEvent(addedRemoteEvent(doc("coll/b", 10, map("matches", false)), targetId));
@@ -464,6 +494,7 @@ public void testDisableIndexAutoCreationWorks() {
     int targetId1 = allocateQuery(query1);
 
     enableIndexAutoCreation();
+    setMinCollectionSizeToAutoCreateIndex(0);
 
     applyRemoteEvent(addedRemoteEvent(doc("coll/a", 10, map("matches", true)), targetId1));
     applyRemoteEvent(addedRemoteEvent(doc("coll/b", 10, map("matches", false)), targetId1));
@@ -509,6 +540,7 @@ public void testIndexAutoCreationWorksWithMutation() {
     int targetId = allocateQuery(query);
 
     enableIndexAutoCreation();
+    setMinCollectionSizeToAutoCreateIndex(0);
 
     applyRemoteEvent(addedRemoteEvent(doc("coll/a", 10, map("matches", true)), targetId));
     applyRemoteEvent(addedRemoteEvent(doc("coll/b", 10, map("matches", false)), targetId));