Github user tdas commented on a diff in the pull request: https://github.com/apache/spark/pull/20698#discussion_r171750580 --- Diff: external/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/KafkaOffsetRangeCalculator.scala --- @@ -0,0 +1,105 @@ +/* + * 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.kafka010 + +import org.apache.kafka.common.TopicPartition + +import org.apache.spark.sql.sources.v2.DataSourceOptions + + +/** + * Class to calculate offset ranges to process based on the the from and until offsets, and + * the configured `minPartitions`. + */ +private[kafka010] class KafkaOffsetRangeCalculator(val minPartitions: Int) { + require(minPartitions >= 0) + + import KafkaOffsetRangeCalculator._ + /** + * Calculate the offset ranges that we are going to process this batch. If `numPartitions` + * is not set or is set less than or equal the number of `topicPartitions` that we're going to + * consume, then we fall back to a 1-1 mapping of Spark tasks to Kafka partitions. If + * `numPartitions` is set higher than the number of our `topicPartitions`, then we will split up + * the read tasks of the skewed partitions to multiple Spark tasks. + * The number of Spark tasks will be *approximately* `numPartitions`. It can be less or more + * depending on rounding errors or Kafka partitions that didn't receive any new data. + */ + def getRanges( + fromOffsets: PartitionOffsetMap, + untilOffsets: PartitionOffsetMap, + executorLocations: Seq[String] = Seq.empty): Seq[KafkaOffsetRange] = { + val partitionsToRead = untilOffsets.keySet.intersect(fromOffsets.keySet) --- End diff -- `fromOffsets` here will contain the initial offsets of new partitions. See the how fromOffsets is set with `startOffsets + newPartitionInitialOffsets`.
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