fix(spanner): skip empty async cache updates

Author: rahul2393

java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/ChannelFinder.java

@@ -117,6 +117,20 @@ private PendingCacheUpdate(CacheUpdate update) {
     }
   }
 
+  private boolean isMaterialUpdate(CacheUpdate update) {
+    return update.getGroupCount() > 0
+        || update.getRangeCount() > 0
+        || (update.hasKeyRecipes() && update.getKeyRecipes().getRecipeCount() > 0);
+  }
+
+  private boolean shouldProcessUpdate(CacheUpdate update) {
+    if (isMaterialUpdate(update)) {
+      return true;
+    }
+    long updateDatabaseId = update.getDatabaseId();
+    return updateDatabaseId != 0 && databaseId.get() != updateDatabaseId;
+  }
+
   public void update(CacheUpdate update) {
     synchronized (updateLock) {
       long currentId = databaseId.get();
@@ -154,6 +168,9 @@ public void update(CacheUpdate update) {
   }
 
   public void updateAsync(CacheUpdate update) {
+    if (!shouldProcessUpdate(update)) {
+      return;
+    }
     pendingUpdates.add(new PendingCacheUpdate(update));
     if (drainScheduled.compareAndSet(false, true)) {
       java.util.concurrent.CountDownLatch latch = new java.util.concurrent.CountDownLatch(1);

java-spanner/google-cloud-spanner/src/test/java/com/google/cloud/spanner/spi/v1/ChannelFinderTest.java

@@ -88,6 +88,30 @@ public void updateIgnoresZeroDatabaseIdAndKeepsExistingCache() throws Exception
     assertThat(rangeCache(finder).size()).isEqualTo(1);
   }
 
+  @Test
+  public void updateAsyncSkipsTrulyEmptyUpdateForCurrentDatabase() throws Exception {
+    ChannelFinder finder = new ChannelFinder(new FakeEndpointCache());
+    finder.update(singleRangeUpdate(0));
+
+    finder.updateAsync(CacheUpdate.newBuilder().setDatabaseId(7L).build());
+    finder.awaitPendingUpdates();
+
+    assertThat(databaseId(finder)).isEqualTo(7L);
+    assertThat(rangeCache(finder).size()).isEqualTo(1);
+  }
+
+  @Test
+  public void updateAsyncProcessesDatabaseTransitionWithoutRangesOrGroups() throws Exception {
+    ChannelFinder finder = new ChannelFinder(new FakeEndpointCache());
+    finder.update(singleRangeUpdate(0));
+
+    finder.updateAsync(CacheUpdate.newBuilder().setDatabaseId(9L).build());
+    finder.awaitPendingUpdates();
+
+    assertThat(databaseId(finder)).isEqualTo(9L);
+    assertThat(rangeCache(finder).size()).isEqualTo(0);
+  }
+
   private static CacheUpdate singleRangeUpdate(int index) {
     String startKey = String.format("k%05d", index);
     String limitKey = String.format("k%05d", index + 1);