[HUDI-3595] Fixing NULL schema provider for empty batch

hudi-common/src/main/java/org/apache/hudi/common/util/CommitUtils.java

@@ -27,6 +27,7 @@
 import org.apache.hudi.common.table.timeline.HoodieTimeline;
 import org.apache.hudi.exception.HoodieException;
 
+import org.apache.avro.Schema;
 import org.apache.log4j.LogManager;
 import org.apache.log4j.Logger;
 
@@ -40,6 +41,7 @@
 public class CommitUtils {
 
   private static final Logger LOG = LogManager.getLogger(CommitUtils.class);
+  private static final String NULL_SCHEMA_STR = Schema.create(Schema.Type.NULL).toString();
 
   /**
    * Gets the commit action type for given write operation and table type.
@@ -84,7 +86,8 @@ public static HoodieCommitMetadata buildMetadata(List<HoodieWriteStat> writeStat
     if (extraMetadata.isPresent()) {
       extraMetadata.get().forEach(commitMetadata::addMetadata);
     }
-    commitMetadata.addMetadata(HoodieCommitMetadata.SCHEMA_KEY, schemaToStoreInCommit == null ? "" : schemaToStoreInCommit);
+    commitMetadata.addMetadata(HoodieCommitMetadata.SCHEMA_KEY, (schemaToStoreInCommit == null || schemaToStoreInCommit.equals(NULL_SCHEMA_STR))
+        ? "" : schemaToStoreInCommit);
     commitMetadata.setOperationType(operationType);
     return commitMetadata;
   }

hudi-utilities/src/test/java/org/apache/hudi/utilities/functional/TestHoodieDeltaStreamer.java

@@ -70,6 +70,7 @@
 import org.apache.hudi.utilities.sources.ParquetDFSSource;
 import org.apache.hudi.utilities.sources.SqlSource;
 import org.apache.hudi.utilities.sources.TestDataSource;
+import org.apache.hudi.utilities.sources.TestParquetDFSSourceEmptyBatch;
 import org.apache.hudi.utilities.testutils.JdbcTestUtils;
 import org.apache.hudi.utilities.testutils.UtilitiesTestBase;
 import org.apache.hudi.utilities.testutils.sources.DistributedTestDataSource;
@@ -130,6 +131,7 @@
 import static org.apache.hudi.utilities.schema.RowBasedSchemaProvider.HOODIE_RECORD_STRUCT_NAME;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -1420,15 +1422,34 @@ private void prepareParquetDFSSource(boolean useSchemaProvider, boolean hasTrans
   }
 
   private void testParquetDFSSource(boolean useSchemaProvider, List<String> transformerClassNames) throws Exception {
+    testParquetDFSSource(useSchemaProvider, transformerClassNames, false);
+  }
+
+  private void testParquetDFSSource(boolean useSchemaProvider, List<String> transformerClassNames, boolean testEmptyBatch) throws Exception {
     prepareParquetDFSSource(useSchemaProvider, transformerClassNames != null);
     String tableBasePath = dfsBasePath + "/test_parquet_table" + testNum;
     HoodieDeltaStreamer deltaStreamer = new HoodieDeltaStreamer(
-        TestHelpers.makeConfig(tableBasePath, WriteOperationType.INSERT, ParquetDFSSource.class.getName(),
+        TestHelpers.makeConfig(tableBasePath, WriteOperationType.INSERT, testEmptyBatch ? TestParquetDFSSourceEmptyBatch.class.getName()
+                : ParquetDFSSource.class.getName(),
             transformerClassNames, PROPS_FILENAME_TEST_PARQUET, false,
             useSchemaProvider, 100000, false, null, null, "timestamp", null), jsc);
     deltaStreamer.sync();
     TestHelpers.assertRecordCount(PARQUET_NUM_RECORDS, tableBasePath + "/*/*.parquet", sqlContext);
     testNum++;
+
+    if (testEmptyBatch) {
+      prepareParquetDFSFiles(100, PARQUET_SOURCE_ROOT, "2.parquet", false, null, null);
+      // parquet source to return empty batch
+      TestParquetDFSSourceEmptyBatch.returnEmptyBatch = true;
+      deltaStreamer.sync();
+      // since we mimic'ed empty batch, total records should be same as first sync().
+      TestHelpers.assertRecordCount(PARQUET_NUM_RECORDS, tableBasePath + "/*/*.parquet", sqlContext);
+      HoodieTableMetaClient metaClient = HoodieTableMetaClient.builder().setBasePath(tableBasePath).setConf(jsc.hadoopConfiguration()).build();
+
+      // validate table schema fetches valid schema from last but one commit.
+      TableSchemaResolver tableSchemaResolver = new TableSchemaResolver(metaClient);
+      assertNotEquals(tableSchemaResolver.getTableAvroSchema(), Schema.create(Schema.Type.NULL).toString());
+    }
   }
 
   private void testORCDFSSource(boolean useSchemaProvider, List<String> transformerClassNames) throws Exception {
@@ -1584,6 +1605,11 @@ public void testParquetDFSSourceWithoutSchemaProviderAndNoTransformer() throws E
     testParquetDFSSource(false, null);
   }
 
+  @Test
+  public void testParquetDFSSourceForEmptyBatch() throws Exception {
+    testParquetDFSSource(false, null, true);
+  }
+
   @Test
   public void testParquetDFSSourceWithoutSchemaProviderAndTransformer() throws Exception {
     testParquetDFSSource(false, Collections.singletonList(TripsWithDistanceTransformer.class.getName()));

hudi-utilities/src/test/java/org/apache/hudi/utilities/sources/TestParquetDFSSourceEmptyBatch.java

@@ -0,0 +1,49 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.hudi.utilities.sources;
+
+import org.apache.hudi.common.config.TypedProperties;
+import org.apache.hudi.common.util.Option;
+import org.apache.hudi.common.util.collection.Pair;
+import org.apache.hudi.utilities.schema.SchemaProvider;
+
+import org.apache.spark.api.java.JavaSparkContext;
+import org.apache.spark.sql.Dataset;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.SparkSession;
+
+public class TestParquetDFSSourceEmptyBatch extends ParquetDFSSource {
+
+  public static boolean returnEmptyBatch;
+
+  public TestParquetDFSSourceEmptyBatch(TypedProperties props, JavaSparkContext sparkContext, SparkSession sparkSession,
+                                        SchemaProvider schemaProvider) {
+    super(props, sparkContext, sparkSession, schemaProvider);
+  }
+
+  @Override
+  public Pair<Option<Dataset<Row>>, String> fetchNextBatch(Option<String> lastCkptStr, long sourceLimit) {
+    Pair<Option<Dataset<Row>>, String> toReturn = super.fetchNextBatch(lastCkptStr, sourceLimit);
+    if (returnEmptyBatch) {
+      return Pair.of(Option.empty(), toReturn.getRight());
+    }
+    return toReturn;
+  }
+}