Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/22009#discussion_r208438810 --- Diff: sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/streaming/ContinuousReadSupport.java --- @@ -0,0 +1,72 @@ +/* + * 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.streaming; + +import org.apache.spark.annotation.InterfaceStability; +import org.apache.spark.sql.execution.streaming.BaseStreamingSource; +import org.apache.spark.sql.sources.v2.reader.InputPartition; +import org.apache.spark.sql.sources.v2.reader.ScanConfig; +import org.apache.spark.sql.sources.v2.reader.ScanConfigBuilder; + +/** + * An interface which defines how to scan the data from data source for streaming processing with + * continuous mode. + */ +@InterfaceStability.Evolving +public interface ContinuousReadSupport extends StreamingReadSupport, BaseStreamingSource { + + /** + * Returns a builder of {@link ScanConfig}. The builder can take some query specific information + * like which operators to pushdown, streaming offsets, etc., and keep these information in the + * created {@link ScanConfig}. + * + * This is the first step of the data scan. All other methods in {@link ContinuousReadSupport} + * needs to take {@link ScanConfig} as an input. + * + * If this method fails (by throwing an exception), the action will fail and no Spark job will be + * submitted. + */ + ScanConfigBuilder newScanConfigBuilder(Offset start); + + /** + * Returns a factory to produce {@link ContinuousPartitionReader}s for {@link InputPartition}s. + * + * If this method fails (by throwing an exception), the action will fail and no Spark job will be + * submitted. + */ + @Override + ContinuousPartitionReaderFactory createReaderFactory(ScanConfig config); --- End diff -- I did it in many places, to allow a data source to implement both batch and streaming without conflicts. But here is a little different, `ContinuousPartitionReaderFactory` is a child of `PartitionReaderFactory`, which means a data source can return `ContinuousPartitionReaderFactory` for both batch and streaming.
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