Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/22009#discussion_r208438912
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/streaming/MicroBatchReadSupport.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.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.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
+ * micro-batch mode.
+ */
+@InterfaceStability.Evolving
+public interface MicroBatchReadSupport 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
MicroBatchReadSupport}
+ * 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, Offset end);
+
+ /**
+ * Returns the most recent offset available.
+ */
+ Offset latestOffset(Offset start);
--- End diff --
a concrete example is in kafka data source, it needs to know the start
offset to decide the latest offset, for purposes like rate control.
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