Enable LRU GC (#68)

* Enable LRU GC

* Add public api and comment to CACHE_SIZE_UNLIMITED

* Switch default for LRU collection to disabled

Author: Greg Soltis

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestore.java

@@ -220,12 +220,7 @@ private void ensureClientConfigured() {
           new DatabaseInfo(databaseId, persistenceKey, settings.getHost(), settings.isSslEnabled());
 
       client =
-          new FirestoreClient(
-              context,
-              databaseInfo,
-              settings.isPersistenceEnabled(),
-              credentialsProvider,
-              asyncQueue);
+          new FirestoreClient(context, databaseInfo, settings, credentialsProvider, asyncQueue);
     }
   }
 

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestoreSettings.java

@@ -24,6 +24,18 @@
 /** Settings used to configure a FirebaseFirestore instance. */
 @PublicApi
 public final class FirebaseFirestoreSettings {
+  /**
+   * Constant to use with {@link FirebaseFirestoreSettings.Builder#setCacheSizeBytes(long)} to
+   * disable garbage collection.
+   */
+  @PublicApi public static final long CACHE_SIZE_UNLIMITED = -1;
+
+  private static final long MINIMUM_CACHE_BYTES = 1 * 1024 * 1024; // 1 MB
+  // TODO(b/121269744): Set this to be the default value after SDK is past version 1.0
+  // private static final long DEFAULT_CACHE_SIZE_BYTES = 100 * 1024 * 1024; // 100 MB
+  // For now, we are rolling this out with collection disabled. Once the SDK has hit version 1.0,
+  // we will switch the default to the above value, 100 MB.
+  private static final long DEFAULT_CACHE_SIZE_BYTES = CACHE_SIZE_UNLIMITED;
   private static final String DEFAULT_HOST = "firestore.googleapis.com";
   private static final boolean DEFAULT_TIMESTAMPS_IN_SNAPSHOTS_ENABLED = false;
 
@@ -34,6 +46,7 @@ public static final class Builder {
     private boolean sslEnabled;
     private boolean persistenceEnabled;
     private boolean timestampsInSnapshotsEnabled;
+    private long cacheSizeBytes;
 
     /** Constructs a new FirebaseFirestoreSettings Builder object. */
     @PublicApi
@@ -42,6 +55,7 @@ public Builder() {
       sslEnabled = true;
       persistenceEnabled = true;
       timestampsInSnapshotsEnabled = DEFAULT_TIMESTAMPS_IN_SNAPSHOTS_ENABLED;
+      cacheSizeBytes = DEFAULT_CACHE_SIZE_BYTES;
     }
 
     /**
@@ -124,6 +138,30 @@ public Builder setTimestampsInSnapshotsEnabled(boolean value) {
       return this;
     }
 
+    /**
+     * Sets an approximate cache size threshold for the on-disk data. If the cache grows beyond this
+     * size, Firestore will start removing data that hasn't been recently used. The size is not a
+     * guarantee that the cache will stay below that size, only that if the cache exceeds the given
+     * size, cleanup will be attempted.
+     *
+     * <p>By default, collection is disabled (the value is set to {@link
+     * FirebaseFirestoreSettings#CACHE_SIZE_UNLIMITED}). In a future release, collection will be
+     * enabled by default, with a default cache size of 100 MB. The minimum value is 1 MB.
+     *
+     * @return A settings object on which the cache size is configured as specified by the given
+     *     {@code value}.
+     */
+    @NonNull
+    @PublicApi
+    public Builder setCacheSizeBytes(long value) {
+      if (value != CACHE_SIZE_UNLIMITED && value < MINIMUM_CACHE_BYTES) {
+        throw new IllegalArgumentException(
+            "Cache size must be set to at least " + MINIMUM_CACHE_BYTES + " bytes");
+      }
+      this.cacheSizeBytes = value;
+      return this;
+    }
+
     @NonNull
     @PublicApi
     public FirebaseFirestoreSettings build() {
@@ -139,13 +177,15 @@ public FirebaseFirestoreSettings build() {
   private final boolean sslEnabled;
   private final boolean persistenceEnabled;
   private final boolean timestampsInSnapshotsEnabled;
+  private final long cacheSizeBytes;
 
   /** Constructs a FirebaseFirestoreSettings object based on the values in the Builder. */
   private FirebaseFirestoreSettings(Builder builder) {
     host = builder.host;
     sslEnabled = builder.sslEnabled;
     persistenceEnabled = builder.persistenceEnabled;
     timestampsInSnapshotsEnabled = builder.timestampsInSnapshotsEnabled;
+    cacheSizeBytes = builder.cacheSizeBytes;
   }
 
   @Override
@@ -161,7 +201,8 @@ public boolean equals(@Nullable Object o) {
     return host.equals(that.host)
         && sslEnabled == that.sslEnabled
         && persistenceEnabled == that.persistenceEnabled
-        && timestampsInSnapshotsEnabled == that.timestampsInSnapshotsEnabled;
+        && timestampsInSnapshotsEnabled == that.timestampsInSnapshotsEnabled
+        && cacheSizeBytes == that.cacheSizeBytes;
   }
 
   @Override
@@ -170,6 +211,7 @@ public int hashCode() {
     result = 31 * result + (sslEnabled ? 1 : 0);
     result = 31 * result + (persistenceEnabled ? 1 : 0);
     result = 31 * result + (timestampsInSnapshotsEnabled ? 1 : 0);
+    result = 31 * result + (int) cacheSizeBytes;
     return result;
   }
 
@@ -211,4 +253,13 @@ public boolean isPersistenceEnabled() {
   public boolean areTimestampsInSnapshotsEnabled() {
     return timestampsInSnapshotsEnabled;
   }
+
+  /**
+   * Returns the threshold for the cache size above which the SDK will attempt to collect the least
+   * recently used documents.
+   */
+  @PublicApi
+  public long getCacheSizeBytes() {
+    return cacheSizeBytes;
+  }
 }

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

@@ -27,11 +27,14 @@
 import com.google.firebase.firestore.EventListener;
 import com.google.firebase.firestore.FirebaseFirestoreException;
 import com.google.firebase.firestore.FirebaseFirestoreException.Code;
+import com.google.firebase.firestore.FirebaseFirestoreSettings;
 import com.google.firebase.firestore.auth.CredentialsProvider;
 import com.google.firebase.firestore.auth.User;
 import com.google.firebase.firestore.core.EventManager.ListenOptions;
 import com.google.firebase.firestore.local.LocalSerializer;
 import com.google.firebase.firestore.local.LocalStore;
+import com.google.firebase.firestore.local.LruDelegate;
+import com.google.firebase.firestore.local.LruGarbageCollector;
 import com.google.firebase.firestore.local.MemoryPersistence;
 import com.google.firebase.firestore.local.Persistence;
 import com.google.firebase.firestore.local.SQLitePersistence;
@@ -71,10 +74,13 @@ public final class FirestoreClient implements RemoteStore.RemoteStoreCallback {
   private SyncEngine syncEngine;
   private EventManager eventManager;
 
+  // LRU-related
+  @Nullable private LruGarbageCollector.Scheduler lruScheduler;
+
   public FirestoreClient(
       final Context context,
       DatabaseInfo databaseInfo,
-      final boolean usePersistence,
+      FirebaseFirestoreSettings settings,
       CredentialsProvider credentialsProvider,
       final AsyncQueue asyncQueue) {
     this.databaseInfo = databaseInfo;
@@ -105,7 +111,11 @@ public FirestoreClient(
           try {
             // Block on initial user being available
             User initialUser = Tasks.await(firstUser.getTask());
-            initialize(context, initialUser, usePersistence);
+            initialize(
+                context,
+                initialUser,
+                settings.isPersistenceEnabled(),
+                settings.getCacheSizeBytes());
           } catch (InterruptedException | ExecutionException e) {
             throw new RuntimeException(e);
           }
@@ -127,6 +137,9 @@ public Task<Void> shutdown() {
         () -> {
           remoteStore.shutdown();
           persistence.shutdown();
+          if (lruScheduler != null) {
+            lruScheduler.stop();
+          }
         });
   }
 
@@ -194,24 +207,38 @@ public <TResult> Task<TResult> transaction(
         () -> syncEngine.transaction(asyncQueue, updateFunction, retries));
   }
 
-  private void initialize(Context context, User user, boolean usePersistence) {
+  private void initialize(Context context, User user, boolean usePersistence, long cacheSizeBytes) {
     // Note: The initialization work must all be synchronous (we can't dispatch more work) since
     // external write/listen operations could get queued to run before that subsequent work
     // completes.
     Logger.debug(LOG_TAG, "Initializing. user=%s", user.getUid());
 
+    LruGarbageCollector gc = null;
     if (usePersistence) {
       LocalSerializer serializer =
           new LocalSerializer(new RemoteSerializer(databaseInfo.getDatabaseId()));
-      persistence =
+      LruGarbageCollector.Params params =
+          LruGarbageCollector.Params.WithCacheSizeBytes(cacheSizeBytes);
+      SQLitePersistence sqlitePersistence =
           new SQLitePersistence(
-              context, databaseInfo.getPersistenceKey(), databaseInfo.getDatabaseId(), serializer);
+              context,
+              databaseInfo.getPersistenceKey(),
+              databaseInfo.getDatabaseId(),
+              serializer,
+              params);
+      LruDelegate lruDelegate = sqlitePersistence.getReferenceDelegate();
+      gc = lruDelegate.getGarbageCollector();
+      persistence = sqlitePersistence;
     } else {
       persistence = MemoryPersistence.createEagerGcMemoryPersistence();
     }
 
     persistence.start();
     localStore = new LocalStore(persistence, user);
+    if (gc != null) {
+      lruScheduler = gc.newScheduler(asyncQueue, localStore);
+      lruScheduler.start();
+    }
 
     Datastore datastore = new Datastore(databaseInfo, asyncQueue, credentialsProvider, context);
     remoteStore = new RemoteStore(this, localStore, datastore, asyncQueue);

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

@@ -570,4 +570,8 @@ private void applyWriteToRemoteDocuments(MutationBatchResult batchResult) {
 
     mutationQueue.removeMutationBatch(batch);
   }
+
+  public LruGarbageCollector.Results collectGarbage(LruGarbageCollector garbageCollector) {
+    return persistence.runTransaction("Collect garbage", () -> garbageCollector.collect(targetIds));
+  }
 }

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

@@ -21,12 +21,12 @@
  * Persistence layers intending to use LRU Garbage collection should implement this interface. This
  * interface defines the operations that the LRU garbage collector needs from the persistence layer.
  */
-interface LruDelegate {
+public interface LruDelegate {
 
   /** Enumerates all the targets in the QueryCache. */
   void forEachTarget(Consumer<QueryData> consumer);
 
-  long getTargetCount();
+  long getSequenceNumberCount();
 
   /** Enumerates sequence numbers for documents not associated with a target. */
   void forEachOrphanedDocumentSequenceNumber(Consumer<Long> consumer);
@@ -49,4 +49,7 @@ interface LruDelegate {
 
   /** Access to the underlying LRU Garbage collector instance. */
   LruGarbageCollector getGarbageCollector();
+
+  /** Return the size of the cache in bytes. */
+  long getByteSize();
 }