Github user jose-torres commented on a diff in the pull request: https://github.com/apache/spark/pull/22009#discussion_r208372469 --- Diff: sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/streaming/StreamingReadSupport.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.sql.sources.v2.reader.ReadSupport; + +/** + * A base interface for streaming read support. This is package private and is invisible to data + * sources. Data sources should implement concrete streaming read support interfaces: + * {@link MicroBatchReadSupport} or {@link ContinuousReadSupport}. + */ +interface StreamingReadSupport extends ReadSupport { + + /** + * Returns the initial offset for a streaming query to start reading from. Note that the + * streaming data source should not assume that it will start reading from its + * {@link #initialOffset()} value: if Spark is restarting an existing query, it will restart from + * the check-pointed offset rather than the initial one. + */ + Offset initialOffset(); + + /** + * Deserialize a JSON string into an Offset of the implementation-defined offset type. + * + * @throws IllegalArgumentException if the JSON does not encode a valid offset for this reader + */ + Offset deserializeOffset(String json); --- End diff -- The offsets are ultimately exposed as JSON inside the JSON representation of StreamingQueryProgress. It's important for visibility and debuggability that progress events contain human-readable representations of offsets.
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