Serve OR queries from the index. (#3368)

* Serve or queries from the index.

* Update test.

* Clean up.

* Move LogicUtils to 'util' directory.

* Reuse existing code for finding least recent index offset.

* Add missing function to MemoryIndexManager

* Add license to new file.

* Address comments.

* Address comments.

Author: ehsannas

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

@@ -20,13 +20,10 @@
 import androidx.annotation.VisibleForTesting;
 import com.google.firebase.firestore.model.Document;
 import com.google.firebase.firestore.model.DocumentKey;
-import com.google.firebase.firestore.model.FieldIndex;
 import com.google.firebase.firestore.model.FieldIndex.IndexOffset;
 import com.google.firebase.firestore.util.AsyncQueue;
 import com.google.firebase.firestore.util.Logger;
-import java.util.Collection;
 import java.util.HashSet;
-import java.util.Iterator;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
@@ -130,8 +127,7 @@ private int writeIndexEntries() {
   private int writeEntriesForCollectionGroup(
       String collectionGroup, int documentsRemainingUnderCap) {
     // Use the earliest offset of all field indexes to query the local cache.
-    Collection<FieldIndex> fieldIndexes = indexManager.getFieldIndexes(collectionGroup);
-    IndexOffset existingOffset = getExistingOffset(fieldIndexes);
+    IndexOffset existingOffset = indexManager.getMinOffset(collectionGroup);
 
     LocalDocumentsResult nextBatch =
         localDocumentsView.getNextDocuments(
@@ -159,24 +155,6 @@ private IndexOffset getNewOffset(IndexOffset existingOffset, LocalDocumentsResul
         Math.max(lookupResult.getBatchId(), existingOffset.getLargestBatchId()));
   }
 
-  /** Returns the lowest offset for the provided index group. */
-  private IndexOffset getExistingOffset(Collection<FieldIndex> fieldIndexes) {
-    hardAssert(!fieldIndexes.isEmpty(), "Updating collection without indexes");
-
-    Iterator<FieldIndex> it = fieldIndexes.iterator();
-    IndexOffset minOffset = it.next().getIndexState().getOffset();
-    int minBatchId = minOffset.getLargestBatchId();
-    while (it.hasNext()) {
-      IndexOffset newOffset = it.next().getIndexState().getOffset();
-      if (newOffset.compareTo(minOffset) < 0) {
-        minOffset = newOffset;
-      }
-      minBatchId = Math.max(newOffset.getLargestBatchId(), minBatchId);
-    }
-
-    return IndexOffset.create(minOffset.getReadTime(), minOffset.getDocumentKey(), minBatchId);
-  }
-
   @VisibleForTesting
   void setMaxDocumentsToProcess(int newMax) {
     maxDocumentsToProcess = newMax;

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

@@ -20,6 +20,7 @@
 import com.google.firebase.firestore.model.Document;
 import com.google.firebase.firestore.model.DocumentKey;
 import com.google.firebase.firestore.model.FieldIndex;
+import com.google.firebase.firestore.model.FieldIndex.IndexOffset;
 import com.google.firebase.firestore.model.ResourcePath;
 import java.util.Collection;
 import java.util.List;
@@ -74,6 +75,18 @@ public interface IndexManager {
   /** Returns all configured field indexes. */
   Collection<FieldIndex> getFieldIndexes();
 
+  /** Returns whether we can serve the given target from an index. */
+  boolean canServeFromIndex(Target target);
+
+  /**
+   * Iterates over all field indexes that are used to serve the given target, and returns the
+   * minimum offset of them all. Asserts that the target can be served from index.
+   */
+  IndexOffset getMinOffset(Target target);
+
+  /** Returns the minimum offset for the given collection group. */
+  IndexOffset getMinOffset(String collectionGroup);
+
   /**
    * Returns an index that can be used to serve the provided target. Returns {@code null} if no
    * index is configured.
@@ -82,7 +95,7 @@ public interface IndexManager {
   FieldIndex getFieldIndex(Target target);
 
   /** Returns the documents that match the given target based on the provided index. */
-  Set<DocumentKey> getDocumentsMatchingTarget(FieldIndex fieldIndex, Target target);
+  Set<DocumentKey> getDocumentsMatchingTarget(Target target);
 
   /** Returns the next collection group to update. Returns {@code null} if no group exists. */
   @Nullable

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

@@ -21,6 +21,7 @@
 import com.google.firebase.firestore.model.Document;
 import com.google.firebase.firestore.model.DocumentKey;
 import com.google.firebase.firestore.model.FieldIndex;
+import com.google.firebase.firestore.model.FieldIndex.IndexOffset;
 import com.google.firebase.firestore.model.ResourcePath;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -69,7 +70,7 @@ public FieldIndex getFieldIndex(Target target) {
 
   @Override
   @Nullable
-  public Set<DocumentKey> getDocumentsMatchingTarget(FieldIndex fieldIndex, Target target) {
+  public Set<DocumentKey> getDocumentsMatchingTarget(Target target) {
     // Field indices are not supported with memory persistence.
     return Collections.emptySet();
   }
@@ -82,7 +83,7 @@ public String getNextCollectionGroupToUpdate() {
   }
 
   @Override
-  public void updateCollectionGroup(String collectionGroup, FieldIndex.IndexOffset offset) {
+  public void updateCollectionGroup(String collectionGroup, IndexOffset offset) {
     // Field indices are not supported with memory persistence.
   }
 
@@ -98,6 +99,21 @@ public Collection<FieldIndex> getFieldIndexes() {
     return Collections.emptyList();
   }
 
+  @Override
+  public boolean canServeFromIndex(Target target) {
+    return false;
+  }
+
+  @Override
+  public IndexOffset getMinOffset(Target target) {
+    return IndexOffset.NONE;
+  }
+
+  @Override
+  public IndexOffset getMinOffset(String collectionGroup) {
+    return IndexOffset.NONE;
+  }
+
   @Override
   public void updateIndexEntries(ImmutableSortedMap<DocumentKey, Document> documents) {
     // Field indices are not supported with memory persistence.

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

@@ -105,22 +105,21 @@ public ImmutableSortedMap<DocumentKey, Document> getDocumentsMatchingQuery(
    */
   private @Nullable ImmutableSortedMap<DocumentKey, Document> performQueryUsingIndex(
       Query query, Target target) {
-    // TODO(orquery): Update this condition when we are able to serve or queries from the index.
-    if (query.matchesAllDocuments() || query.containsCompositeFilters()) {
+    if (query.matchesAllDocuments()) {
       // Don't use index queries that can be executed by scanning the collection.
       return null;
     }
 
-    FieldIndex fieldIndex = indexManager.getFieldIndex(query.toTarget());
-    if (fieldIndex == null) {
+    if (!indexManager.canServeFromIndex(target)) {
       return null;
     }
 
-    Set<DocumentKey> keys = indexManager.getDocumentsMatchingTarget(fieldIndex, target);
+    Set<DocumentKey> keys = indexManager.getDocumentsMatchingTarget(target);
     ImmutableSortedMap<DocumentKey, Document> indexedDocuments =
         localDocumentsView.getDocuments(keys);
+
     return appendRemainingResults(
-        values(indexedDocuments), query, fieldIndex.getIndexState().getOffset());
+        values(indexedDocuments), query, indexManager.getMinOffset(target));
   }
 
   /**
@@ -131,8 +130,7 @@ public ImmutableSortedMap<DocumentKey, Document> getDocumentsMatchingQuery(
       Query query,
       ImmutableSortedSet<DocumentKey> remoteKeys,
       SnapshotVersion lastLimboFreeSnapshotVersion) {
-    // TODO(orquery): Update this condition when we are able to serve or queries from the index.
-    if (query.matchesAllDocuments() || query.containsCompositeFilters()) {
+    if (query.matchesAllDocuments()) {
       // Don't use index queries that can be executed by scanning the collection.
       return null;
     }