Github user tdas commented on a diff in the pull request: https://github.com/apache/spark/pull/17219#discussion_r106738661 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/OffsetCommitLog.scala --- @@ -0,0 +1,79 @@ +/* + * 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.execution.streaming + +import java.io.{InputStream, OutputStream} +import java.nio.charset.StandardCharsets._ + +import scala.io.{Source => IOSource} + +import org.apache.spark.sql.SparkSession + +/** + * Used to write log files that represent commit points in structured streaming. + * A log file will be written immediately after the successful completion of a + * batch, and before processing the next batch. Here is an execution summary: + * - trigger batch 1 + * - obtain batch 1 offsets and write to offset log + * - process batch 1 + * - write batch 1 to commit log + * - trigger batch 2 + * - obtain bactch 2 offsets and write to offset log + * - process batch 2 + * - write batch 2 to commit log + * .... + * + * The current format of the commit log is: + * line 1: version + * line 2: metadata (optional json string) + */ +class OffsetCommitLog(sparkSession: SparkSession, path: String) + extends HDFSMetadataLog[Option[String]](sparkSession, path) { + + override protected def deserialize(in: InputStream): Option[String] = { + // called inside a try-finally where the underlying stream is closed in the caller + val lines = IOSource.fromInputStream(in, UTF_8.name()).getLines() + if (!lines.hasNext) { + throw new IllegalStateException("Incomplete log file") --- End diff -- can you say "incomplete log file in the offset commit log"
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