Github user rdblue commented on a diff in the pull request:
https://github.com/apache/spark/pull/22009#discussion_r208389947
--- 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);
+
+ /**
+ * Merge partitioned offsets coming from {@link
ContinuousPartitionReader} instances
+ * for each partition to a single global offset.
+ */
+ Offset mergeOffsets(PartitionOffset[] offsets);
+
+ /**
+ * The execution engine will call this method in every epoch to
determine if new input
+ * partitions need to be generated, which may be required if for example
the underlying
+ * source system has had partitions added or removed.
+ *
+ * If true, the query will be shut down and restarted with a new {@link
ContinuousReadSupport}
+ * instance.
+ */
+ default boolean needsReconfiguration() {
--- End diff --
I think of a ReadSupport as something that can be read or scanned and
ContinuousReadSupport as a stream that can be read. In that abstraction, the
"something that can be read" probably isn't the right place to track whether a
particular scan requires reconfiguration: a *scan* requires reconfiguration if
that scan is based on partitions that are out of date.
To me, that indicates that a Kafka `ScanConfig` should keep track of kafka
partitions and then `needsReconfiguration` should return true if the Kafka
topic now has a different set of partitions than the ones in the `ScanConfig`.
Does that make sense?
I think it would also be more consistent in the API to add `ScanConfig`
here.
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