Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/16686#discussion_r99332003
--- Diff:
external/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/KafkaTopicPartitionOffsetReader.scala
---
@@ -0,0 +1,300 @@
+/*
+ * 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 java.{util => ju}
+import java.util.concurrent.{Executors, ThreadFactory}
+
+import scala.collection.JavaConverters._
+import scala.concurrent.{ExecutionContext, Future}
+import scala.concurrent.duration.Duration
+import scala.util.control.NonFatal
+
+import org.apache.kafka.clients.consumer.{Consumer, ConsumerConfig,
KafkaConsumer}
+import org.apache.kafka.common.TopicPartition
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.types._
+import org.apache.spark.util.{ThreadUtils, UninterruptibleThread}
+
+/**
+ * This class uses Kafka's own [[KafkaConsumer]] API to read data offsets
from Kafka.
+ * The [[ConsumerStrategy]] class defines which Kafka topics and
partitions should be read
+ * by this source. These strategies directly correspond to the different
consumption options
+ * in. This class is designed to return a configured [[KafkaConsumer]]
that is used by the
+ * [[KafkaSource]] to query for the offsets. See the docs on
+ * [[org.apache.spark.sql.kafka010.ConsumerStrategy]]
+ * for more details.
+ *
+ * Note: This class is not ThreadSafe
+ */
+private[kafka010] class KafkaTopicPartitionOffsetReader(
+ consumerStrategy: ConsumerStrategy,
+ driverKafkaParams: ju.Map[String, Object],
+ readerOptions: Map[String, String],
+ driverGroupIdPrefix: String) extends Logging {
+ /**
+ * Used to ensure execute fetch operations execute in an
UninterruptibleThread
+ */
+ val kafkaReaderThread = Executors.newSingleThreadExecutor(new
ThreadFactory {
+ override def newThread(r: Runnable): Thread = {
+ val t = new UninterruptibleThread("Kafka Offset Reader") {
+ override def run(): Unit = {
+ r.run()
+ }
+ }
+ t.setDaemon(true)
+ t
+ }
+ })
+ val execContext = ExecutionContext.fromExecutorService(kafkaReaderThread)
+
+ /**
+ * A KafkaConsumer used in the driver to query the latest Kafka offsets.
This only queries the
+ * offsets and never commits them.
+ */
+ protected var consumer = createConsumer()
+
+ private val maxOffsetFetchAttempts =
+ readerOptions.getOrElse("fetchOffset.numRetries", "3").toInt
+
+ private val offsetFetchAttemptIntervalMs =
+ readerOptions.getOrElse("fetchOffset.retryIntervalMs", "1000").toLong
+
+ private var groupId: String = null
+
+ private var nextId = 0
+
+ private def nextGroupId(): String = {
+ groupId = driverGroupIdPrefix + "-" + nextId
+ nextId += 1
+ groupId
+ }
+
+ override def toString(): String = consumerStrategy.toString
+
+ /**
+ * Closes the connection to Kafka, and cleans up state.
+ */
+ def close(): Unit = {
+ consumer.close()
+ kafkaReaderThread.shutdownNow()
+ }
+
+ /**
+ * @return The Set of TopicPartitions for a given topic
+ */
+ def fetchTopicPartitions(): Set[TopicPartition] = runUninterruptibly {
+ assert(Thread.currentThread().isInstanceOf[UninterruptibleThread])
+ // Poll to get the latest assigned partitions
+ consumer.poll(0)
+ val partitions = consumer.assignment()
+ consumer.pause(partitions)
+ partitions.asScala.toSet
+ }
+
+ /**
+ * Resolves the specific offsets based on Kafka seek positions.
+ * This method resolves offset value -1 to the latest and -2 to the
+ * earliest Kafka seek position.
+ */
+ def fetchSpecificOffsets(
+ partitionOffsets: Map[TopicPartition, Long]): Map[TopicPartition,
Long] =
+ runUninterruptibly {
+ withRetriesWithoutInterrupt {
+ // Poll to get the latest assigned partitions
+ consumer.poll(0)
+ val partitions = consumer.assignment()
+ consumer.pause(partitions)
+ assert(partitions.asScala == partitionOffsets.keySet,
+ "If startingOffsets contains specific offsets, you must specify
all TopicPartitions.\n" +
+ "Use -1 for latest, -2 for earliest, if you don't care.\n" +
+ s"Specified: ${partitionOffsets.keySet} Assigned:
${partitions.asScala}")
+ logDebug(s"Partitions assigned to consumer: $partitions. Seeking
to $partitionOffsets")
+
+ partitionOffsets.foreach {
+ case (tp, KafkaOffsets.LATEST) =>
consumer.seekToEnd(ju.Arrays.asList(tp))
+ case (tp, KafkaOffsets.EARLIEST) =>
consumer.seekToBeginning(ju.Arrays.asList(tp))
+ case (tp, off) => consumer.seek(tp, off)
+ }
+ partitionOffsets.map {
+ case (tp, _) => tp -> consumer.position(tp)
+ }
+ }
+ }
+
+ /**
+ * Fetch the earliest offsets of partitions.
--- End diff --
can you specify which partitions? maybe "offsets of all partitions to be
consumed according the consumer strategy"
same for docs of other methods that do not take a specific list of
partitions.
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