Github user jose-torres commented on a diff in the pull request:
https://github.com/apache/spark/pull/20689#discussion_r171332700
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/ContinuousDataReaderFactory.java
---
@@ -0,0 +1,38 @@
+/*
+ * 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.spark.sql.sources.v2.reader;
+
+import org.apache.spark.annotation.InterfaceStability;
+import org.apache.spark.sql.sources.v2.reader.streaming.PartitionOffset;
+
+/**
+ * A mix-in interface for {@link DataReaderFactory}. Continuous data
reader factories can
+ * implement this interface to provide creating {@link DataReader} with
particular offset.
+ */
+@InterfaceStability.Evolving
+public interface ContinuousDataReaderFactory<T> extends
DataReaderFactory<T> {
+ /**
+ * Create a DataReader with particular offset as its startOffset.
+ *
+ * @param offset offset want to set as the DataReader's startOffset.
+ */
+ default DataReader<T> createDataReaderWithOffset(PartitionOffset offset)
{
+ throw new IllegalStateException(
--- End diff --
I don't know if we want a default here - it seems like subclasses should
always be able to provide an implementation, and thus that we should always
require them to.
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