KAFKA-6361: Fix log divergence between leader and follower after fast leader fail over (#4882)

Implementation of KIP-279 as described here: https://cwiki.apache.org/confluence/display/KAFKA/KIP-279%3A+Fix+log+divergence+between+leader+and+follower+after+fast+leader+fail+over

In summary:
- Added leader_epoch to OFFSET_FOR_LEADER_EPOCH_RESPONSE
- Leader replies with the pair( largest epoch less than or equal to the requested epoch, the end offset of this epoch)
- If Follower does not know about the leader epoch that leader replies with, it truncates to the end offset of largest leader epoch less than leader epoch that leader replied with, and sends another OffsetForLeaderEpoch request. That request contains the largest leader epoch less than leader epoch that leader replied with.

Reviewers: Dong Lin <lindong28@gmail.com>, Jun Rao <junrao@gmail.com>

clients/src/main/java/org/apache/kafka/common/protocol/CommonFields.java

@@ -26,6 +26,7 @@ public class CommonFields {
     public static final Field.Int32 PARTITION_ID = new Field.Int32("partition", "Topic partition id");
     public static final Field.Int16 ERROR_CODE = new Field.Int16("error_code", "Response error code");
     public static final Field.NullableStr ERROR_MESSAGE = new Field.NullableStr("error_message", "Response error message");
+    public static final Field.Int32 LEADER_EPOCH = new Field.Int32("leader_epoch", "The epoch");
 
     // Group APIs
     public static final Field.Str GROUP_ID = new Field.Str("group_id", "The unique group identifier");

clients/src/main/java/org/apache/kafka/common/requests/EpochEndOffset.java

@@ -20,24 +20,29 @@ import org.apache.kafka.common.protocol.Errors;
 
 import static org.apache.kafka.common.record.RecordBatch.NO_PARTITION_LEADER_EPOCH;
 
+import java.util.Objects;
+
 /**
  * The offset, fetched from a leader, for a particular partition.
  */
 
 public class EpochEndOffset {
     public static final long UNDEFINED_EPOCH_OFFSET = NO_PARTITION_LEADER_EPOCH;
-    public static final int UNDEFINED_EPOCH = -1;
+    public static final int UNDEFINED_EPOCH = NO_PARTITION_LEADER_EPOCH;
 
     private Errors error;
+    private int leaderEpoch;  // introduced in V1
     private long endOffset;
 
-    public EpochEndOffset(Errors error, long endOffset) {
+    public EpochEndOffset(Errors error, int leaderEpoch, long endOffset) {
         this.error = error;
+        this.leaderEpoch = leaderEpoch;
         this.endOffset = endOffset;
     }
 
-    public EpochEndOffset(long endOffset) {
+    public EpochEndOffset(int leaderEpoch, long endOffset) {
         this.error = Errors.NONE;
+        this.leaderEpoch = leaderEpoch;
         this.endOffset = endOffset;
     }
 
@@ -53,10 +58,15 @@ public class EpochEndOffset {
         return endOffset;
     }
 
+    public int leaderEpoch() {
+        return leaderEpoch;
+    }
+
     @Override
     public String toString() {
         return "EpochEndOffset{" +
                 "error=" + error +
+                ", leaderEpoch=" + leaderEpoch +
                 ", endOffset=" + endOffset +
                 '}';
     }
@@ -68,14 +78,13 @@ public class EpochEndOffset {
 
         EpochEndOffset that = (EpochEndOffset) o;
 
-        if (error != that.error) return false;
+        return Objects.equals(error, that.error)
-        return endOffset == that.endOffset;
+               && Objects.equals(leaderEpoch, that.leaderEpoch)
+               && Objects.equals(endOffset, that.endOffset);
     }
 
     @Override
     public int hashCode() {
-        int result = (int) error.code();
+        return Objects.hash(error, leaderEpoch, endOffset);
-        result = 31 * result + (int) (endOffset ^ (endOffset >>> 32));
-        return result;
     }
 }

clients/src/main/java/org/apache/kafka/common/requests/OffsetsForLeaderEpochRequest.java

@@ -50,8 +50,11 @@ public class OffsetsForLeaderEpochRequest extends AbstractRequest {
     private static final Schema OFFSET_FOR_LEADER_EPOCH_REQUEST_V0 = new Schema(
             new Field(TOPICS_KEY_NAME, new ArrayOf(OFFSET_FOR_LEADER_EPOCH_REQUEST_TOPIC_V0), "An array of topics to get epochs for"));
 
+    /* v1 request is the same as v0. Per-partition leader epoch has been added to response */
+    private static final Schema OFFSET_FOR_LEADER_EPOCH_REQUEST_V1 = OFFSET_FOR_LEADER_EPOCH_REQUEST_V0;
+
     public static Schema[] schemaVersions() {
-        return new Schema[]{OFFSET_FOR_LEADER_EPOCH_REQUEST_V0};
+        return new Schema[]{OFFSET_FOR_LEADER_EPOCH_REQUEST_V0, OFFSET_FOR_LEADER_EPOCH_REQUEST_V1};
     }
 
     private Map<TopicPartition, Integer> epochsByPartition;
@@ -63,12 +66,12 @@ public class OffsetsForLeaderEpochRequest extends AbstractRequest {
     public static class Builder extends AbstractRequest.Builder<OffsetsForLeaderEpochRequest> {
         private Map<TopicPartition, Integer> epochsByPartition = new HashMap<>();
 
-        public Builder() {
+        public Builder(short version) {
-            super(ApiKeys.OFFSET_FOR_LEADER_EPOCH);
+            super(ApiKeys.OFFSET_FOR_LEADER_EPOCH, version);
         }
 
-        public Builder(Map<TopicPartition, Integer> epochsByPartition) {
+        public Builder(short version, Map<TopicPartition, Integer> epochsByPartition) {
-            super(ApiKeys.OFFSET_FOR_LEADER_EPOCH);
+            super(ApiKeys.OFFSET_FOR_LEADER_EPOCH, version);
             this.epochsByPartition = epochsByPartition;
         }
 
@@ -150,7 +153,8 @@ public class OffsetsForLeaderEpochRequest extends AbstractRequest {
         Errors error = Errors.forException(e);
         Map<TopicPartition, EpochEndOffset> errorResponse = new HashMap<>();
         for (TopicPartition tp : epochsByPartition.keySet()) {
-            errorResponse.put(tp, new EpochEndOffset(error, EpochEndOffset.UNDEFINED_EPOCH_OFFSET));
+            errorResponse.put(tp, new EpochEndOffset(
+                error, EpochEndOffset.UNDEFINED_EPOCH, EpochEndOffset.UNDEFINED_EPOCH_OFFSET));
         }
         return new OffsetsForLeaderEpochResponse(errorResponse);
     }

clients/src/main/java/org/apache/kafka/common/requests/OffsetsForLeaderEpochResponse.java

@@ -23,6 +23,7 @@ import org.apache.kafka.common.protocol.types.ArrayOf;
 import org.apache.kafka.common.protocol.types.Field;
 import org.apache.kafka.common.protocol.types.Schema;
 import org.apache.kafka.common.protocol.types.Struct;
+import org.apache.kafka.common.record.RecordBatch;
 import org.apache.kafka.common.utils.CollectionUtils;
 
 import java.nio.ByteBuffer;
@@ -34,6 +35,7 @@ import java.util.Map;
 import static org.apache.kafka.common.protocol.CommonFields.ERROR_CODE;
 import static org.apache.kafka.common.protocol.CommonFields.PARTITION_ID;
 import static org.apache.kafka.common.protocol.CommonFields.TOPIC_NAME;
+import static org.apache.kafka.common.protocol.CommonFields.LEADER_EPOCH;
 import static org.apache.kafka.common.protocol.types.Type.INT64;
 
 public class OffsetsForLeaderEpochResponse extends AbstractResponse {
@@ -52,8 +54,23 @@ public class OffsetsForLeaderEpochResponse extends AbstractResponse {
             new Field(TOPICS_KEY_NAME, new ArrayOf(OFFSET_FOR_LEADER_EPOCH_RESPONSE_TOPIC_V0),
                     "An array of topics for which we have leader offsets for some requested Partition Leader Epoch"));
 
+
+    // OFFSET_FOR_LEADER_EPOCH_RESPONSE_PARTITION_V1 added a per-partition leader epoch field,
+    // which specifies which leader epoch the end offset belongs to
+    private static final Schema OFFSET_FOR_LEADER_EPOCH_RESPONSE_PARTITION_V1 = new Schema(
+            ERROR_CODE,
+            PARTITION_ID,
+            LEADER_EPOCH,
+            new Field(END_OFFSET_KEY_NAME, INT64, "The end offset"));
+    private static final Schema OFFSET_FOR_LEADER_EPOCH_RESPONSE_TOPIC_V1 = new Schema(
+            TOPIC_NAME,
+            new Field(PARTITIONS_KEY_NAME, new ArrayOf(OFFSET_FOR_LEADER_EPOCH_RESPONSE_PARTITION_V1)));
+    private static final Schema OFFSET_FOR_LEADER_EPOCH_RESPONSE_V1 = new Schema(
+            new Field(TOPICS_KEY_NAME, new ArrayOf(OFFSET_FOR_LEADER_EPOCH_RESPONSE_TOPIC_V1),
+                  "An array of topics for which we have leader offsets for some requested Partition Leader Epoch"));
+
     public static Schema[] schemaVersions() {
-        return new Schema[]{OFFSET_FOR_LEADER_EPOCH_RESPONSE_V0};
+        return new Schema[]{OFFSET_FOR_LEADER_EPOCH_RESPONSE_V0, OFFSET_FOR_LEADER_EPOCH_RESPONSE_V1};
     }
 
     private Map<TopicPartition, EpochEndOffset> epochEndOffsetsByPartition;
@@ -68,8 +85,9 @@ public class OffsetsForLeaderEpochResponse extends AbstractResponse {
                 Errors error = Errors.forCode(partitionAndEpoch.get(ERROR_CODE));
                 int partitionId = partitionAndEpoch.get(PARTITION_ID);
                 TopicPartition tp = new TopicPartition(topic, partitionId);
+                int leaderEpoch = partitionAndEpoch.getOrElse(LEADER_EPOCH, RecordBatch.NO_PARTITION_LEADER_EPOCH);
                 long endOffset = partitionAndEpoch.getLong(END_OFFSET_KEY_NAME);
-                epochEndOffsetsByPartition.put(tp, new EpochEndOffset(error, endOffset));
+                epochEndOffsetsByPartition.put(tp, new EpochEndOffset(error, leaderEpoch, endOffset));
             }
         }
     }
@@ -110,6 +128,7 @@ public class OffsetsForLeaderEpochResponse extends AbstractResponse {
                 Struct partitionStruct = topicStruct.instance(PARTITIONS_KEY_NAME);
                 partitionStruct.set(ERROR_CODE, partitionEndOffset.getValue().error().code());
                 partitionStruct.set(PARTITION_ID, partitionEndOffset.getKey());
+                partitionStruct.setIfExists(LEADER_EPOCH, partitionEndOffset.getValue().leaderEpoch());
                 partitionStruct.set(END_OFFSET_KEY_NAME, partitionEndOffset.getValue().endOffset());
                 partitions.add(partitionStruct);
             }

clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java

@@ -1020,15 +1020,15 @@ public class RequestResponseTest {
         epochs.put(new TopicPartition("topic1", 1), 1);
         epochs.put(new TopicPartition("topic2", 2), 3);
 
-        return new OffsetsForLeaderEpochRequest.Builder(epochs).build();
+        return new OffsetsForLeaderEpochRequest.Builder(ApiKeys.OFFSET_FOR_LEADER_EPOCH.latestVersion(), epochs).build();
     }
 
     private OffsetsForLeaderEpochResponse createLeaderEpochResponse() {
         Map<TopicPartition, EpochEndOffset> epochs = new HashMap<>();
 
-        epochs.put(new TopicPartition("topic1", 0), new EpochEndOffset(Errors.NONE, 0));
+        epochs.put(new TopicPartition("topic1", 0), new EpochEndOffset(Errors.NONE, 1, 0));
-        epochs.put(new TopicPartition("topic1", 1), new EpochEndOffset(Errors.NONE, 1));
+        epochs.put(new TopicPartition("topic1", 1), new EpochEndOffset(Errors.NONE, 1, 1));
-        epochs.put(new TopicPartition("topic2", 2), new EpochEndOffset(Errors.NONE, 2));
+        epochs.put(new TopicPartition("topic2", 2), new EpochEndOffset(Errors.NONE, 1, 2));
 
         return new OffsetsForLeaderEpochResponse(epochs);
     }

core/src/main/scala/kafka/api/ApiVersion.scala

@@ -77,6 +77,7 @@ object ApiVersion {
     // and KafkaStorageException for fetch requests.
     "1.1-IV0" -> KAFKA_1_1_IV0,
     "1.1" -> KAFKA_1_1_IV0,
+    // Introduced OffsetsForLeaderEpochRequest V1 via KIP-279
     "2.0-IV0" -> KAFKA_2_0_IV0,
     "2.0" -> KAFKA_2_0_IV0
   )

core/src/main/scala/kafka/cluster/Partition.scala

@@ -647,15 +647,20 @@ class Partition(val topic: String,
 
   /**
     * @param leaderEpoch Requested leader epoch
-    * @return The last offset of messages published under this leader epoch.
+    * @return The requested leader epoch and the end offset of this leader epoch, or if the requested
+    *         leader epoch is unknown, the leader epoch less than the requested leader epoch and the end offset
+    *         of this leader epoch. The end offset of a leader epoch is defined as the start
+    *         offset of the first leader epoch larger than the leader epoch, or else the log end
+    *         offset if the leader epoch is the latest leader epoch.
     */
   def lastOffsetForLeaderEpoch(leaderEpoch: Int): EpochEndOffset = {
     inReadLock(leaderIsrUpdateLock) {
       leaderReplicaIfLocal match {
         case Some(leaderReplica) =>
-          new EpochEndOffset(NONE, leaderReplica.epochs.get.endOffsetFor(leaderEpoch))
+          val (epoch, offset) = leaderReplica.epochs.get.endOffsetFor(leaderEpoch)
+          new EpochEndOffset(NONE, epoch, offset)
         case None =>
-          new EpochEndOffset(NOT_LEADER_FOR_PARTITION, UNDEFINED_EPOCH_OFFSET)
+          new EpochEndOffset(NOT_LEADER_FOR_PARTITION, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
       }
     }
   }

core/src/main/scala/kafka/consumer/ConsumerFetcherThread.scala

@@ -20,7 +20,7 @@ package kafka.consumer
 import kafka.api.{FetchRequestBuilder, FetchResponsePartitionData, OffsetRequest, Request}
 import kafka.cluster.BrokerEndPoint
 import kafka.message.ByteBufferMessageSet
-import kafka.server.{AbstractFetcherThread, PartitionFetchState}
+import kafka.server.{AbstractFetcherThread, PartitionFetchState, OffsetTruncationState}
 import AbstractFetcherThread.ResultWithPartitions
 import kafka.common.{ErrorMapping, TopicAndPartition}
 
@@ -129,7 +129,7 @@ class ConsumerFetcherThread(consumerIdString: String,
 
   override def fetchEpochsFromLeader(partitions: Map[TopicPartition, Int]): Map[TopicPartition, EpochEndOffset] = { Map() }
 
-  override def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, Long]] = {
+  override def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, OffsetTruncationState]] = {
     ResultWithPartitions(Map(), Set())
   }
 }

core/src/main/scala/kafka/server/AbstractFetcherThread.scala

@@ -19,9 +19,10 @@ package kafka.server
 
 import java.util.concurrent.locks.ReentrantLock
 
-import kafka.cluster.BrokerEndPoint
+import kafka.cluster.{Replica, BrokerEndPoint}
 import kafka.utils.{DelayedItem, Pool, ShutdownableThread}
 import org.apache.kafka.common.errors.{CorruptRecordException, KafkaStorageException}
+import org.apache.kafka.common.requests.EpochEndOffset._
 import kafka.common.{ClientIdAndBroker, KafkaException}
 import kafka.metrics.KafkaMetricsGroup
 import kafka.utils.CoreUtils.inLock
@@ -39,6 +40,8 @@ import org.apache.kafka.common.internals.{FatalExitError, PartitionStates}
 import org.apache.kafka.common.record.MemoryRecords
 import org.apache.kafka.common.requests.EpochEndOffset
 
+import scala.math._
+
 /**
  *  Abstract class for fetching data from multiple partitions from the same broker.
  */
@@ -76,7 +79,7 @@ abstract class AbstractFetcherThread(name: String,
 
   protected def fetchEpochsFromLeader(partitions: Map[TopicPartition, Int]): Map[TopicPartition, EpochEndOffset]
 
-  protected def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, Long]]
+  protected def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, OffsetTruncationState]]
 
   protected def buildFetchRequest(partitionMap: Seq[(TopicPartition, PartitionFetchState)]): ResultWithPartitions[REQ]
 
@@ -132,7 +135,7 @@ abstract class AbstractFetcherThread(name: String,
         val leaderEpochs = fetchedEpochs.filter { case (tp, _) => partitionStates.contains(tp) }
         val ResultWithPartitions(fetchOffsets, partitionsWithError) = maybeTruncate(leaderEpochs)
         handlePartitionsWithErrors(partitionsWithError)
-        markTruncationCompleteAndUpdateFetchOffset(fetchOffsets)
+        updateFetchOffsetAndMaybeMarkTruncationComplete(fetchOffsets)
       }
     }
   }
@@ -272,15 +275,16 @@ abstract class AbstractFetcherThread(name: String,
   }
 
   /**
-    * Loop through all partitions, marking them as truncation complete and update the fetch offset
+    * Loop through all partitions, updating their fetch offset and maybe marking them as
+    * truncation completed if their offsetTruncationState indicates truncation completed
     *
-    * @param fetchOffsets the partitions to mark truncation complete
+    * @param fetchOffsets the partitions to update fetch offset and maybe mark truncation complete
     */
-  private def markTruncationCompleteAndUpdateFetchOffset(fetchOffsets: Map[TopicPartition, Long]) {
+  private def updateFetchOffsetAndMaybeMarkTruncationComplete(fetchOffsets: Map[TopicPartition, OffsetTruncationState]) {
     val newStates: Map[TopicPartition, PartitionFetchState] = partitionStates.partitionStates.asScala
       .map { state =>
         val maybeTruncationComplete = fetchOffsets.get(state.topicPartition()) match {
-          case Some(offset) => PartitionFetchState(offset, state.value.delay, truncatingLog = false)
+          case Some(offsetTruncationState) => PartitionFetchState(offsetTruncationState.offset, state.value.delay, truncatingLog = !offsetTruncationState.truncationCompleted)
           case None => state.value()
         }
         (state.topicPartition(), maybeTruncationComplete)
@@ -288,6 +292,79 @@ abstract class AbstractFetcherThread(name: String,
     partitionStates.set(newStates.asJava)
   }
 
+  /**
+   * Called from ReplicaFetcherThread and ReplicaAlterLogDirsThread maybeTruncate for each topic
+   * partition. Returns truncation offset and whether this is the final offset to truncate to
+   *
+   * For each topic partition, the offset to truncate to is calculated based on leader's returned
+   * epoch and offset:
+   *  -- If the leader replied with undefined epoch offset, we must use the high watermark. This can
+   *  happen if 1) the leader is still using message format older than KAFKA_0_11_0; 2) the follower
+   *  requested leader epoch < the first leader epoch known to the leader.
+   *  -- If the leader replied with the valid offset but undefined leader epoch, we truncate to
+   *  leader's offset if it is lower than follower's Log End Offset. This may happen if the
+   *  leader is on the inter-broker protocol version < KAFKA_2_0_IV0
+   *  -- If the leader replied with leader epoch not known to the follower, we truncate to the
+   *  end offset of the largest epoch that is smaller than the epoch the leader replied with, and
+   *  send OffsetsForLeaderEpochRequest with that leader epoch. In a more rare case, where the
+   *  follower was not tracking epochs smaller than the epoch the leader replied with, we
+   *  truncate the leader's offset (and do not send any more leader epoch requests).
+   *  -- Otherwise, truncate to min(leader's offset, end offset on the follower for epoch that
+   *  leader replied with, follower's Log End Offset).
+   *
+   * @param tp                    Topic partition
+   * @param leaderEpochOffset     Epoch end offset received from the leader for this topic partition
+   * @param replica               Follower's replica, which is either local replica
+   *                              (ReplicaFetcherThread) or future replica (ReplicaAlterLogDirsThread)
+   * @param isFutureReplica       true if called from ReplicaAlterLogDirsThread
+   */
+  def getOffsetTruncationState(tp: TopicPartition, leaderEpochOffset: EpochEndOffset, replica: Replica, isFutureReplica: Boolean = false): OffsetTruncationState = {
+    // to make sure we can distinguish log output for fetching from remote leader or local replica
+    val followerName = if (isFutureReplica) "future replica" else "follower"
+
+    if (leaderEpochOffset.endOffset == UNDEFINED_EPOCH_OFFSET) {
+      // truncate to initial offset which is the high watermark for follower replica. For
+      // future replica, it is either high watermark of the future replica or current
+      // replica's truncation offset (when the current replica truncates, it forces future
+      // replica's partition state to 'truncating' and sets initial offset to its truncation offset)
+      warn(s"Based on $followerName's leader epoch, leader replied with an unknown offset in ${replica.topicPartition}. " +
+           s"The initial fetch offset ${partitionStates.stateValue(tp).fetchOffset} will be used for truncation.")
+      OffsetTruncationState(partitionStates.stateValue(tp).fetchOffset, truncationCompleted = true)
+    } else if (leaderEpochOffset.leaderEpoch == UNDEFINED_EPOCH) {
+      // either leader or follower or both use inter-broker protocol version < KAFKA_2_0_IV0
+      // (version 0 of OffsetForLeaderEpoch request/response)
+      warn(s"Leader or $followerName is on protocol version where leader epoch is not considered in the OffsetsForLeaderEpoch response. " +
+           s"The leader's offset ${leaderEpochOffset.endOffset} will be used for truncation in ${replica.topicPartition}.")
+      OffsetTruncationState(min(leaderEpochOffset.endOffset, replica.logEndOffset.messageOffset), truncationCompleted = true)
+    } else {
+      // get (leader epoch, end offset) pair that corresponds to the largest leader epoch
+      // less than or equal to the requested epoch.
+      val (followerEpoch, followerEndOffset) = replica.epochs.get.endOffsetFor(leaderEpochOffset.leaderEpoch)
+      if (followerEndOffset == UNDEFINED_EPOCH_OFFSET) {
+        // This can happen if the follower was not tracking leader epochs at that point (before the
+        // upgrade, or if this broker is new). Since the leader replied with epoch <
+        // requested epoch from follower, so should be safe to truncate to leader's
+        // offset (this is the same behavior as post-KIP-101 and pre-KIP-279)
+        warn(s"Based on $followerName's leader epoch, leader replied with epoch ${leaderEpochOffset.leaderEpoch} " +
+             s"below any $followerName's tracked epochs for ${replica.topicPartition}. " +
+             s"The leader's offset only ${leaderEpochOffset.endOffset} will be used for truncation.")
+        OffsetTruncationState(min(leaderEpochOffset.endOffset, replica.logEndOffset.messageOffset), truncationCompleted = true)
+      } else if (followerEpoch != leaderEpochOffset.leaderEpoch) {
+        // the follower does not know about the epoch that leader replied with
+        // we truncate to the end offset of the largest epoch that is smaller than the
+        // epoch the leader replied with, and send another offset for leader epoch request
+        val intermediateOffsetToTruncateTo = min(followerEndOffset, replica.logEndOffset.messageOffset)
+        info(s"Based on $followerName's leader epoch, leader replied with epoch ${leaderEpochOffset.leaderEpoch} " +
+             s"unknown to the $followerName for ${replica.topicPartition}. " +
+             s"Will truncate to $intermediateOffsetToTruncateTo and send another leader epoch request to the leader.")
+        OffsetTruncationState(intermediateOffsetToTruncateTo, truncationCompleted = false)
+      } else {
+        val offsetToTruncateTo = min(followerEndOffset, leaderEpochOffset.endOffset)
+        OffsetTruncationState(min(offsetToTruncateTo, replica.logEndOffset.messageOffset), truncationCompleted = true)
+      }
+    }
+  }
+
   def delayPartitions(partitions: Iterable[TopicPartition], delay: Long) {
     partitionMapLock.lockInterruptibly()
     try {
@@ -446,3 +523,10 @@ case class PartitionFetchState(fetchOffset: Long, delay: DelayedItem, truncating
 
   override def toString = "offset:%d-isReadyForFetch:%b-isTruncatingLog:%b".format(fetchOffset, isReadyForFetch, truncatingLog)
 }
+
+case class OffsetTruncationState(offset: Long, truncationCompleted: Boolean) {
+
+  def this(offset: Long) = this(offset, true)
+
+  override def toString = "offset:%d-truncationCompleted:%b".format(offset, truncationCompleted)
+}

core/src/main/scala/kafka/server/ReplicaAlterLogDirsThread.scala

@@ -37,7 +37,6 @@ import org.apache.kafka.common.record.{FileRecords, MemoryRecords}
 import scala.collection.JavaConverters._
 import scala.collection.{Map, Seq, Set, mutable}
 
-
 class ReplicaAlterLogDirsThread(name: String,
                                 sourceBroker: BrokerEndPoint,
                                 brokerConfig: KafkaConfig,
@@ -102,7 +101,8 @@ class ReplicaAlterLogDirsThread(name: String,
 
     // Append the leader's messages to the log
     partition.appendRecordsToFutureReplica(records)
-    futureReplica.highWatermark = new LogOffsetMetadata(partitionData.highWatermark)
+    val futureReplicaHighWatermark = futureReplica.logEndOffset.messageOffset.min(partitionData.highWatermark)
+    futureReplica.highWatermark = new LogOffsetMetadata(futureReplicaHighWatermark)
     futureReplica.maybeIncrementLogStartOffset(partitionData.logStartOffset)
 
     if (partition.maybeReplaceCurrentWithFutureReplica())
@@ -164,17 +164,32 @@ class ReplicaAlterLogDirsThread(name: String,
   def fetchEpochsFromLeader(partitions: Map[TopicPartition, Int]): Map[TopicPartition, EpochEndOffset] = {
     partitions.map { case (tp, epoch) =>
       try {
-        tp -> new EpochEndOffset(Errors.NONE, replicaMgr.getReplicaOrException(tp).epochs.get.endOffsetFor(epoch))
+        val (leaderEpoch, leaderOffset) = replicaMgr.getReplicaOrException(tp).epochs.get.endOffsetFor(epoch)
+        tp -> new EpochEndOffset(Errors.NONE, leaderEpoch, leaderOffset)
       } catch {
         case t: Throwable =>
           warn(s"Error when getting EpochEndOffset for $tp", t)
-          tp -> new EpochEndOffset(Errors.forException(t), UNDEFINED_EPOCH_OFFSET)
+          tp -> new EpochEndOffset(Errors.forException(t), UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
       }
     }
   }
 
-  def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, Long]] = {
+  /**
-    val fetchOffsets = scala.collection.mutable.HashMap.empty[TopicPartition, Long]
+   * Truncate the log for each partition based on current replica's returned epoch and offset.
+   *
+   * The logic for finding the truncation offset is the same as in ReplicaFetcherThread
+   * and mainly implemented in AbstractFetcherThread.getOffsetTruncationState. One difference is
+   * that the initial fetch offset for topic partition could be set to the truncation offset of
+   * the current replica if that replica truncates. Otherwise, it is high watermark as in ReplicaFetcherThread.
+   *
+   * The reason we have to follow the leader epoch approach for truncating a future replica is to
+   * cover the case where a future replica is offline when the current replica truncates and
+   * re-replicates offsets that may have already been copied to the future replica. In that case,
+   * the future replica may miss "mark for truncation" event and must use the offset for leader epoch
+   * exchange with the current replica to truncate to the largest common log prefix for the topic partition
+   */
+  def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, OffsetTruncationState]] = {
+    val fetchOffsets = scala.collection.mutable.HashMap.empty[TopicPartition, OffsetTruncationState]
     val partitionsWithError = mutable.Set[TopicPartition]()
 
     fetchedEpochs.foreach { case (topicPartition, epochOffset) =>
@@ -186,16 +201,10 @@ class ReplicaAlterLogDirsThread(name: String,
           info(s"Retrying leaderEpoch request for partition $topicPartition as the current replica reported an error: ${epochOffset.error}")
           partitionsWithError += topicPartition
         } else {
-          val fetchOffset =
+          val offsetTruncationState = getOffsetTruncationState(topicPartition, epochOffset, futureReplica, isFutureReplica = true)
-            if (epochOffset.endOffset == UNDEFINED_EPOCH_OFFSET)
-              partitionStates.stateValue(topicPartition).fetchOffset
-            else if (epochOffset.endOffset >= futureReplica.logEndOffset.messageOffset)
-              futureReplica.logEndOffset.messageOffset
-            else
-              epochOffset.endOffset
 
-          partition.truncateTo(fetchOffset, isFuture = true)
+          partition.truncateTo(offsetTruncationState.offset, isFuture = true)
-          fetchOffsets.put(topicPartition, fetchOffset)
+          fetchOffsets.put(topicPartition, offsetTruncationState)
         }
       } catch {
         case e: KafkaStorageException =>

core/src/main/scala/kafka/server/ReplicaFetcherThread.scala

@@ -21,7 +21,7 @@ import java.util
 
 import AbstractFetcherThread.ResultWithPartitions
 import kafka.api.{FetchRequest => _, _}
-import kafka.cluster.{BrokerEndPoint, Replica}
+import kafka.cluster.BrokerEndPoint
 import kafka.log.LogConfig
 import kafka.server.ReplicaFetcherThread._
 import kafka.server.epoch.LeaderEpochCache
@@ -74,6 +74,9 @@ class ReplicaFetcherThread(name: String,
     else if (brokerConfig.interBrokerProtocolVersion >= KAFKA_0_10_0_IV0) 2
     else if (brokerConfig.interBrokerProtocolVersion >= KAFKA_0_9_0) 1
     else 0
+  private val offsetForLeaderEpochRequestVersion: Short =
+    if (brokerConfig.interBrokerProtocolVersion >= KAFKA_2_0_IV0) 1
+    else 0
   private val fetchMetadataSupported = brokerConfig.interBrokerProtocolVersion >= KAFKA_1_1_IV0
   private val maxWait = brokerConfig.replicaFetchWaitMaxMs
   private val minBytes = brokerConfig.replicaFetchMinBytes
@@ -286,37 +289,31 @@ class ReplicaFetcherThread(name: String,
   }
 
   /**
-    * - Truncate the log to the leader's offset for each partition's epoch.
+   * Truncate the log for each partition's epoch based on leader's returned epoch and offset.
-    * - If the leader's offset is greater, we stick with the Log End Offset
+   * The logic for finding the truncation offset is implemented in AbstractFetcherThread.getOffsetTruncationState
-    *   otherwise we truncate to the leaders offset.
-    * - If the leader replied with undefined epoch offset we must use the high watermark
    */
-  override def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, Long]] = {
+  override def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, OffsetTruncationState]] = {
-    val fetchOffsets = scala.collection.mutable.HashMap.empty[TopicPartition, Long]
+    val fetchOffsets = scala.collection.mutable.HashMap.empty[TopicPartition, OffsetTruncationState]
     val partitionsWithError = mutable.Set[TopicPartition]()
 
-    fetchedEpochs.foreach { case (tp, epochOffset) =>
+    fetchedEpochs.foreach { case (tp, leaderEpochOffset) =>
       try {
         val replica = replicaMgr.getReplicaOrException(tp)
         val partition = replicaMgr.getPartition(tp).get
 
-        if (epochOffset.hasError) {
+        if (leaderEpochOffset.hasError) {
-          info(s"Retrying leaderEpoch request for partition ${replica.topicPartition} as the leader reported an error: ${epochOffset.error}")
+          info(s"Retrying leaderEpoch request for partition ${replica.topicPartition} as the leader reported an error: ${leaderEpochOffset.error}")
           partitionsWithError += tp
         } else {
-          val fetchOffset =
+          val offsetTruncationState = getOffsetTruncationState(tp, leaderEpochOffset, replica)
-            if (epochOffset.endOffset == UNDEFINED_EPOCH_OFFSET) {
+          if (offsetTruncationState.offset < replica.highWatermark.messageOffset)
-              warn(s"Based on follower's leader epoch, leader replied with an unknown offset in ${replica.topicPartition}. " +
+            warn(s"Truncating $tp to offset ${offsetTruncationState.offset} below high watermark ${replica.highWatermark.messageOffset}")
-                s"The initial fetch offset ${partitionStates.stateValue(tp).fetchOffset} will be used for truncation.")
-              partitionStates.stateValue(tp).fetchOffset
-            } else if (epochOffset.endOffset >= replica.logEndOffset.messageOffset)
-              logEndOffset(replica, epochOffset)
-            else
-              epochOffset.endOffset
 
-          partition.truncateTo(fetchOffset, isFuture = false)
+          partition.truncateTo(offsetTruncationState.offset, isFuture = false)
-          replicaMgr.replicaAlterLogDirsManager.markPartitionsForTruncation(brokerConfig.brokerId, tp, fetchOffset)
+          // mark the future replica for truncation only when we do last truncation
-          fetchOffsets.put(tp, fetchOffset)
+          if (offsetTruncationState.truncationCompleted)
+            replicaMgr.replicaAlterLogDirsManager.markPartitionsForTruncation(brokerConfig.brokerId, tp, offsetTruncationState.offset)
+          fetchOffsets.put(tp, offsetTruncationState)
         }
       } catch {
         case e: KafkaStorageException =>
@@ -344,7 +341,7 @@ class ReplicaFetcherThread(name: String,
     var result: Map[TopicPartition, EpochEndOffset] = null
     if (shouldSendLeaderEpochRequest) {
       val partitionsAsJava = partitions.map { case (tp, epoch) => tp -> epoch.asInstanceOf[Integer] }.toMap.asJava
-      val epochRequest = new OffsetsForLeaderEpochRequest.Builder(partitionsAsJava)
+      val epochRequest = new OffsetsForLeaderEpochRequest.Builder(offsetForLeaderEpochRequestVersion, partitionsAsJava)
       try {
         val response = leaderEndpoint.sendRequest(epochRequest)
         result = response.responseBody.asInstanceOf[OffsetsForLeaderEpochResponse].responses.asScala
@@ -355,26 +352,19 @@ class ReplicaFetcherThread(name: String,
 
           // if we get any unexpected exception, mark all partitions with an error
           result = partitions.map { case (tp, _) =>
-            tp -> new EpochEndOffset(Errors.forException(t), UNDEFINED_EPOCH_OFFSET)
+            tp -> new EpochEndOffset(Errors.forException(t), UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
           }
       }
     } else {
       // just generate a response with no error but UNDEFINED_OFFSET so that we can fall back to truncating using
       // high watermark in maybeTruncate()
       result = partitions.map { case (tp, _) =>
-        tp -> new EpochEndOffset(Errors.NONE, UNDEFINED_EPOCH_OFFSET)
+        tp -> new EpochEndOffset(Errors.NONE, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
       }
     }
     result
   }
 
-  private def logEndOffset(replica: Replica, epochOffset: EpochEndOffset): Long = {
-    val logEndOffset = replica.logEndOffset.messageOffset
-    info(s"Based on follower's leader epoch, leader replied with an offset ${epochOffset.endOffset} >= the " +
-      s"follower's log end offset $logEndOffset in ${replica.topicPartition}. No truncation needed.")
-    logEndOffset
-  }
-
   /**
    *  To avoid ISR thrashing, we only throttle a replica on the follower if it's in the throttled replica list,
    *  the quota is exceeded and the replica is not in sync.

core/src/main/scala/kafka/server/ReplicaManager.scala

@@ -1475,11 +1475,11 @@ class ReplicaManager(val config: KafkaConfig,
       val epochEndOffset = getPartition(tp) match {
         case Some(partition) =>
           if (partition eq ReplicaManager.OfflinePartition)
-            new EpochEndOffset(KAFKA_STORAGE_ERROR, UNDEFINED_EPOCH_OFFSET)
+            new EpochEndOffset(KAFKA_STORAGE_ERROR, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
           else
             partition.lastOffsetForLeaderEpoch(leaderEpoch)
         case None =>
-          new EpochEndOffset(UNKNOWN_TOPIC_OR_PARTITION, UNDEFINED_EPOCH_OFFSET)
+          new EpochEndOffset(UNKNOWN_TOPIC_OR_PARTITION, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
       }
       tp -> epochEndOffset
     }

core/src/main/scala/kafka/server/epoch/LeaderEpochFileCache.scala

@@ -20,7 +20,7 @@ import java.util.concurrent.locks.ReentrantReadWriteLock
 
 import kafka.server.LogOffsetMetadata
 import kafka.server.checkpoints.LeaderEpochCheckpoint
-import org.apache.kafka.common.requests.EpochEndOffset.{UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET}
+import org.apache.kafka.common.requests.EpochEndOffset._
 import kafka.utils.CoreUtils._
 import kafka.utils.Logging
 import org.apache.kafka.common.TopicPartition
@@ -29,7 +29,7 @@ import scala.collection.mutable.ListBuffer
 trait LeaderEpochCache {
   def assign(leaderEpoch: Int, offset: Long)
   def latestEpoch(): Int
-  def endOffsetFor(epoch: Int): Long
+  def endOffsetFor(epoch: Int): (Int, Long)
   def clearAndFlushLatest(offset: Long)
   def clearAndFlushEarliest(offset: Long)
   def clearAndFlush()
@@ -81,36 +81,42 @@ class LeaderEpochFileCache(topicPartition: TopicPartition, leo: () => LogOffsetM
   }
 
   /**
-    * Returns the End Offset for a requested Leader Epoch.
+    * Returns the Leader Epoch and the End Offset for a requested Leader Epoch.
     *
-    * This is defined as the start offset of the first Leader Epoch larger than the
+    * The Leader Epoch returned is the largest epoch less than or equal to the requested Leader
-    * Leader Epoch requested, or else the Log End Offset if the latest epoch was requested.
+    * Epoch. The End Offset is the end offset of this epoch, which is defined as the start offset
+    * of the first Leader Epoch larger than the Leader Epoch requested, or else the Log End
+    * Offset if the latest epoch was requested.
     *
     * During the upgrade phase, where there are existing messages may not have a leader epoch,
     * if requestedEpoch is < the first epoch cached, UNSUPPORTED_EPOCH_OFFSET will be returned
     * so that the follower falls back to High Water Mark.
     *
-    * @param requestedEpoch
+    * @param requestedEpoch requested leader epoch
-    * @return offset
+    * @return leader epoch and offset
     */
-  override def endOffsetFor(requestedEpoch: Int): Long = {
+  override def endOffsetFor(requestedEpoch: Int): (Int, Long) = {
     inReadLock(lock) {
-      val offset =
+      val epochAndOffset =
         if (requestedEpoch == UNDEFINED_EPOCH) {
           // this may happen if a bootstrapping follower sends a request with undefined epoch or
           // a follower is on the older message format where leader epochs are not recorded
-          UNDEFINED_EPOCH_OFFSET
+          (UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
         } else if (requestedEpoch == latestEpoch) {
-          leo().messageOffset
+          (requestedEpoch, leo().messageOffset)
         } else {
-          val subsequentEpochs = epochs.filter(e => e.epoch > requestedEpoch)
+          val (subsequentEpochs, previousEpochs) = epochs.partition { e => e.epoch > requestedEpoch}
           if (subsequentEpochs.isEmpty || requestedEpoch < epochs.head.epoch)
-            UNDEFINED_EPOCH_OFFSET
+            // no epochs recorded or requested epoch < the first epoch cached
-          else
+            (UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
-            subsequentEpochs.head.startOffset
+          else {
+            // we must get at least one element in previous epochs list, because if we are here,
+            // it means that requestedEpoch >= epochs.head.epoch -- so at least the first epoch is
+            (previousEpochs.last.epoch, subsequentEpochs.head.startOffset)
           }
-      debug(s"Processed offset for epoch request for partition ${topicPartition} epoch:$requestedEpoch and returning offset $offset from epoch list of size ${epochs.size}")
+        }
-      offset
+      debug(s"Processed offset for epoch request for partition ${topicPartition} epoch:$requestedEpoch and returning epoch ${epochAndOffset._1} and offset ${epochAndOffset._2} from epoch list of size ${epochs.size}")
+      epochAndOffset
     }
   }
 

core/src/test/scala/integration/kafka/api/AuthorizerIntegrationTest.scala

@@ -290,7 +290,7 @@ class AuthorizerIntegrationTest extends BaseRequestTest {
   }
 
   private def offsetsForLeaderEpochRequest = {
-    new OffsetsForLeaderEpochRequest.Builder().add(tp, 7).build()
+    new OffsetsForLeaderEpochRequest.Builder(ApiKeys.OFFSET_FOR_LEADER_EPOCH.latestVersion()).add(tp, 7).build()
   }
 
   private def createOffsetFetchRequest = {

core/src/test/scala/unit/kafka/server/AbstractFetcherThreadTest.scala

@@ -21,6 +21,7 @@ import AbstractFetcherThread._
 import com.yammer.metrics.Metrics
 import kafka.cluster.BrokerEndPoint
 import kafka.server.AbstractFetcherThread.{FetchRequest, PartitionData}
+import kafka.server.OffsetTruncationState
 import kafka.utils.TestUtils
 import org.apache.kafka.common.TopicPartition
 import org.apache.kafka.common.protocol.Errors
@@ -131,7 +132,7 @@ class AbstractFetcherThreadTest {
 
     override def fetchEpochsFromLeader(partitions: Map[TopicPartition, Int]): Map[TopicPartition, EpochEndOffset] = { Map() }
 
-    override def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, Long]] = {
+    override def maybeTruncate(fetchedEpochs: Map[TopicPartition, EpochEndOffset]): ResultWithPartitions[Map[TopicPartition, OffsetTruncationState]] = {
       ResultWithPartitions(Map(), Set())
     }
   }

core/src/test/scala/unit/kafka/server/ReplicaAlterLogDirsThreadTest.scala

@@ -61,7 +61,7 @@ class ReplicaAlterLogDirsThreadTest {
 
     //Stubs
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
-    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn(leo).anyTimes()
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, leo)).anyTimes()
     stub(replica, replica, futureReplica, partition, replicaManager)
 
     replay(leaderEpochs, replicaManager, replica)
@@ -78,8 +78,8 @@ class ReplicaAlterLogDirsThreadTest {
     val result = thread.fetchEpochsFromLeader(Map(t1p0 -> leaderEpoch, t1p1 -> leaderEpoch))
 
     val expected = Map(
-      t1p0 -> new EpochEndOffset(Errors.NONE, leo),
+      t1p0 -> new EpochEndOffset(Errors.NONE, leaderEpoch, leo),
-      t1p1 -> new EpochEndOffset(Errors.NONE, leo)
+      t1p1 -> new EpochEndOffset(Errors.NONE, leaderEpoch, leo)
     )
 
     assertEquals("results from leader epoch request should have offset from local replica",
@@ -101,7 +101,7 @@ class ReplicaAlterLogDirsThreadTest {
 
     //Stubs
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
-    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn(leo).anyTimes()
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, leo)).anyTimes()
     expect(replicaManager.getReplicaOrException(t1p0)).andReturn(replica).anyTimes()
     expect(replicaManager.getPartition(t1p0)).andReturn(Some(partition)).anyTimes()
     expect(replicaManager.getReplicaOrException(t1p1)).andThrow(new KafkaStorageException).once()
@@ -121,8 +121,8 @@ class ReplicaAlterLogDirsThreadTest {
     val result = thread.fetchEpochsFromLeader(Map(t1p0 -> leaderEpoch, t1p1 -> leaderEpoch))
 
     val expected = Map(
-      t1p0 -> new EpochEndOffset(Errors.NONE, leo),
+      t1p0 -> new EpochEndOffset(Errors.NONE, leaderEpoch, leo),
-      t1p1 -> new EpochEndOffset(Errors.KAFKA_STORAGE_ERROR, UNDEFINED_EPOCH_OFFSET)
+      t1p1 -> new EpochEndOffset(Errors.KAFKA_STORAGE_ERROR, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
     )
 
     assertEquals(expected, result)
@@ -161,8 +161,10 @@ class ReplicaAlterLogDirsThreadTest {
     expect(futureReplica.epochs).andReturn(Some(futureReplicaLeaderEpochs)).anyTimes()
     expect(futureReplica.logEndOffset).andReturn(new LogOffsetMetadata(futureReplicaLEO)).anyTimes()
     expect(futureReplicaLeaderEpochs.latestEpoch).andReturn(leaderEpoch).anyTimes()
-    expect(leaderEpochsT1p0.endOffsetFor(leaderEpoch)).andReturn(replicaT1p0LEO).anyTimes()
+    expect(leaderEpochsT1p0.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, replicaT1p0LEO)).anyTimes()
-    expect(leaderEpochsT1p1.endOffsetFor(leaderEpoch)).andReturn(replicaT1p1LEO).anyTimes()
+    expect(leaderEpochsT1p1.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, replicaT1p1LEO)).anyTimes()
+    expect(futureReplicaLeaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, futureReplicaLEO)).anyTimes()
+
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     stubWithFetchMessages(replicaT1p0, replicaT1p1, futureReplica, partition, replicaManager, responseCallback)
 
@@ -188,6 +190,73 @@ class ReplicaAlterLogDirsThreadTest {
     assertTrue(truncateToCapture.getValues.asScala.contains(futureReplicaLEO))
   }
 
+  @Test
+  def shouldTruncateToEndOffsetOfLargestCommonEpoch(): Unit = {
+
+    //Create a capture to track what partitions/offsets are truncated
+    val truncateToCapture: Capture[Long] = newCapture(CaptureType.ALL)
+
+    // Setup all the dependencies
+    val config = KafkaConfig.fromProps(TestUtils.createBrokerConfig(1, "localhost:1234"))
+    val quotaManager = createNiceMock(classOf[ReplicationQuotaManager])
+    val leaderEpochs = createMock(classOf[LeaderEpochCache])
+    val futureReplicaLeaderEpochs = createMock(classOf[LeaderEpochCache])
+    val logManager = createMock(classOf[LogManager])
+    val replica = createNiceMock(classOf[Replica])
+    // one future replica mock because our mocking methods return same values for both future replicas
+    val futureReplica = createNiceMock(classOf[Replica])
+    val partition = createMock(classOf[Partition])
+    val replicaManager = createMock(classOf[ReplicaManager])
+    val responseCallback: Capture[Seq[(TopicPartition, FetchPartitionData)] => Unit]  = EasyMock.newCapture()
+
+    val leaderEpoch = 5
+    val futureReplicaLEO = 195
+    val replicaLEO = 200
+    val replicaEpochEndOffset = 190
+    val futureReplicaEpochEndOffset = 191
+
+    //Stubs
+    expect(partition.truncateTo(capture(truncateToCapture), anyBoolean())).anyTimes()
+    expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
+    expect(futureReplica.epochs).andReturn(Some(futureReplicaLeaderEpochs)).anyTimes()
+    expect(futureReplica.logEndOffset).andReturn(new LogOffsetMetadata(futureReplicaLEO)).anyTimes()
+    expect(futureReplicaLeaderEpochs.latestEpoch).andReturn(leaderEpoch).once()
+    expect(futureReplicaLeaderEpochs.latestEpoch).andReturn(leaderEpoch - 2).once()
+
+    // leader replica truncated and fetched new offsets with new leader epoch
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch - 1, replicaLEO)).anyTimes()
+    // but future replica does not know about this leader epoch, so returns a smaller leader epoch
+    expect(futureReplicaLeaderEpochs.endOffsetFor(leaderEpoch - 1)).andReturn((leaderEpoch - 2, futureReplicaLEO)).anyTimes()
+    // finally, the leader replica knows about the leader epoch and returns end offset
+    expect(leaderEpochs.endOffsetFor(leaderEpoch - 2)).andReturn((leaderEpoch - 2, replicaEpochEndOffset)).anyTimes()
+    expect(futureReplicaLeaderEpochs.endOffsetFor(leaderEpoch - 2)).andReturn((leaderEpoch - 2, futureReplicaEpochEndOffset)).anyTimes()
+
+    expect(replicaManager.logManager).andReturn(logManager).anyTimes()
+    stubWithFetchMessages(replica, replica, futureReplica, partition, replicaManager, responseCallback)
+
+    replay(leaderEpochs, futureReplicaLeaderEpochs, replicaManager, logManager, quotaManager, replica, futureReplica, partition)
+
+    //Create the thread
+    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
+    val thread = new ReplicaAlterLogDirsThread(
+      "alter-logs-dirs-thread-test1",
+      sourceBroker = endPoint,
+      brokerConfig = config,
+      replicaMgr = replicaManager,
+      quota = quotaManager,
+      brokerTopicStats = null)
+    thread.addPartitions(Map(t1p0 -> 0))
+
+    // First run will result in another offset for leader epoch request
+    thread.doWork()
+    // Second run should actually truncate
+    thread.doWork()
+
+    //We should have truncated to the offsets in the response
+    assertTrue("Expected offset " + replicaEpochEndOffset + " in captured truncation offsets " + truncateToCapture.getValues,
+               truncateToCapture.getValues.asScala.contains(replicaEpochEndOffset))
+  }
+
   @Test
   def shouldTruncateToInitialFetchOffsetIfReplicaReturnsUndefinedOffset(): Unit = {
 
@@ -219,9 +288,9 @@ class ReplicaAlterLogDirsThreadTest {
     // pretend this is a completely new future replica, with no leader epochs recorded
     expect(futureReplicaLeaderEpochs.latestEpoch).andReturn(UNDEFINED_EPOCH).anyTimes()
 
-    // since UNDEFINED_EPOCH is -1 wich will be lower than any valid leader epoch, the method
+    // since UNDEFINED_EPOCH is -1 which will be lower than any valid leader epoch, the method
     // will return UNDEFINED_EPOCH_OFFSET if requested epoch is lower than the first epoch cached
-    expect(leaderEpochs.endOffsetFor(UNDEFINED_EPOCH)).andReturn(UNDEFINED_EPOCH_OFFSET).anyTimes()
+    expect(leaderEpochs.endOffsetFor(UNDEFINED_EPOCH)).andReturn((UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)).anyTimes()
     stubWithFetchMessages(replica, replica, futureReplica, partition, replicaManager, responseCallback)
     replay(replicaManager, logManager, quotaManager, leaderEpochs, futureReplicaLeaderEpochs,
            replica, futureReplica, partition)
@@ -273,7 +342,8 @@ class ReplicaAlterLogDirsThreadTest {
     expect(futureReplica.epochs).andReturn(Some(futureReplicaLeaderEpochs)).anyTimes()
 
     expect(futureReplicaLeaderEpochs.latestEpoch).andReturn(futureReplicaLeaderEpoch).anyTimes()
-    expect(leaderEpochs.endOffsetFor(futureReplicaLeaderEpoch)).andReturn(replicaLEO).anyTimes()
+    expect(leaderEpochs.endOffsetFor(futureReplicaLeaderEpoch)).andReturn((futureReplicaLeaderEpoch, replicaLEO)).anyTimes()
+    expect(futureReplicaLeaderEpochs.endOffsetFor(futureReplicaLeaderEpoch)).andReturn((futureReplicaLeaderEpoch, futureReplicaLEO)).anyTimes()
 
     expect(futureReplica.logEndOffset).andReturn(new LogOffsetMetadata(futureReplicaLEO)).anyTimes()
     expect(replicaManager.getReplica(t1p0)).andReturn(Some(replica)).anyTimes()
@@ -355,7 +425,8 @@ class ReplicaAlterLogDirsThreadTest {
 
     expect(futureReplica.logEndOffset).andReturn(new LogOffsetMetadata(futureReplicaLEO)).anyTimes()
     expect(futureReplicaLeaderEpochs.latestEpoch).andReturn(leaderEpoch)
-    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn(replicaLEO)
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, replicaLEO))
+    expect(futureReplicaLeaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, futureReplicaLEO))
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     stubWithFetchMessages(replica, replica, futureReplica, partition, replicaManager, responseCallback)
 

core/src/test/scala/unit/kafka/server/ReplicaFetcherThreadTest.scala

@@ -20,7 +20,6 @@ import kafka.cluster.{BrokerEndPoint, Replica}
 import kafka.log.LogManager
 import kafka.cluster.Partition
 import kafka.server.epoch.LeaderEpochCache
-import org.apache.kafka.common.requests.EpochEndOffset._
 import kafka.server.epoch.util.ReplicaFetcherMockBlockingSend
 import kafka.utils.TestUtils
 import org.apache.kafka.common.TopicPartition
@@ -28,6 +27,7 @@ import org.apache.kafka.common.metrics.Metrics
 import org.apache.kafka.common.protocol.Errors
 import org.apache.kafka.common.protocol.Errors._
 import org.apache.kafka.common.requests.EpochEndOffset
+import org.apache.kafka.common.requests.EpochEndOffset._
 import org.apache.kafka.common.utils.SystemTime
 import org.easymock.EasyMock._
 import org.easymock.{Capture, CaptureType}
@@ -43,17 +43,18 @@ class ReplicaFetcherThreadTest {
   private val t1p1 = new TopicPartition("topic1", 1)
   private val t2p1 = new TopicPartition("topic2", 1)
 
+  private val brokerEndPoint = new BrokerEndPoint(0, "localhost", 1000)
+
   @Test
   def shouldNotIssueLeaderEpochRequestIfInterbrokerVersionBelow11(): Unit = {
     val props = TestUtils.createBrokerConfig(1, "localhost:1234")
     props.put(KafkaConfig.InterBrokerProtocolVersionProp, "0.10.2")
     props.put(KafkaConfig.LogMessageFormatVersionProp, "0.10.2")
     val config = KafkaConfig.fromProps(props)
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
     val thread = new ReplicaFetcherThread(
       name = "bob",
       fetcherId = 0,
-      sourceBroker = endPoint,
+      sourceBroker = brokerEndPoint,
       brokerConfig = config,
       replicaMgr = null,
       metrics =  new Metrics(),
@@ -64,8 +65,8 @@ class ReplicaFetcherThreadTest {
     val result = thread.fetchEpochsFromLeader(Map(t1p0 -> 0, t1p1 -> 0))
 
     val expected = Map(
-      t1p0 -> new EpochEndOffset(Errors.NONE, UNDEFINED_EPOCH_OFFSET),
+      t1p0 -> new EpochEndOffset(Errors.NONE, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET),
-      t1p1 -> new EpochEndOffset(Errors.NONE, UNDEFINED_EPOCH_OFFSET)
+      t1p1 -> new EpochEndOffset(Errors.NONE, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
     )
 
     assertEquals("results from leader epoch request should have undefined offset", expected, result)
@@ -75,7 +76,6 @@ class ReplicaFetcherThreadTest {
   def shouldHandleExceptionFromBlockingSend(): Unit = {
     val props = TestUtils.createBrokerConfig(1, "localhost:1234")
     val config = KafkaConfig.fromProps(props)
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
     val mockBlockingSend = createMock(classOf[BlockingSend])
 
     expect(mockBlockingSend.sendRequest(anyObject())).andThrow(new NullPointerException).once()
@@ -84,7 +84,7 @@ class ReplicaFetcherThreadTest {
     val thread = new ReplicaFetcherThread(
       name = "bob",
       fetcherId = 0,
-      sourceBroker = endPoint,
+      sourceBroker = brokerEndPoint,
       brokerConfig = config,
       replicaMgr = null,
       metrics =  new Metrics(),
@@ -95,8 +95,8 @@ class ReplicaFetcherThreadTest {
     val result = thread.fetchEpochsFromLeader(Map(t1p0 -> 0, t1p1 -> 0))
 
     val expected = Map(
-      t1p0 -> new EpochEndOffset(Errors.UNKNOWN_SERVER_ERROR, UNDEFINED_EPOCH_OFFSET),
+      t1p0 -> new EpochEndOffset(Errors.UNKNOWN_SERVER_ERROR, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET),
-      t1p1 -> new EpochEndOffset(Errors.UNKNOWN_SERVER_ERROR, UNDEFINED_EPOCH_OFFSET)
+      t1p1 -> new EpochEndOffset(Errors.UNKNOWN_SERVER_ERROR, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
     )
 
     assertEquals("results from leader epoch request should have undefined offset", expected, result)
@@ -104,7 +104,7 @@ class ReplicaFetcherThreadTest {
   }
 
   @Test
-  def shouldFetchLeaderEpochOnFirstFetchOnly(): Unit = {
+  def shouldFetchLeaderEpochOnFirstFetchOnlyIfLeaderEpochKnownToBoth(): Unit = {
     val config = KafkaConfig.fromProps(TestUtils.createBrokerConfig(1, "localhost:1234"))
 
     //Setup all dependencies
@@ -116,27 +116,29 @@ class ReplicaFetcherThreadTest {
     val partition = createMock(classOf[Partition])
     val replicaManager = createMock(classOf[ReplicaManager])
 
+    val leaderEpoch = 5
+
     //Stubs
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
     expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(0)).anyTimes()
-    expect(leaderEpochs.latestEpoch).andReturn(5)
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(0)).anyTimes()
+    expect(leaderEpochs.latestEpoch).andReturn(leaderEpoch)
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, 0)).anyTimes()
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
     stub(replica, partition, replicaManager)
 
-
     //Expectations
     expect(partition.truncateTo(anyLong(), anyBoolean())).once
 
     replay(leaderEpochs, replicaManager, logManager, quota, replica)
 
     //Define the offsets for the OffsetsForLeaderEpochResponse
-    val offsets = Map(t1p0 -> new EpochEndOffset(1), t1p1 -> new EpochEndOffset(1)).asJava
+    val offsets = Map(t1p0 -> new EpochEndOffset(leaderEpoch, 1), t1p1 -> new EpochEndOffset(leaderEpoch, 1)).asJava
 
     //Create the fetcher thread
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsets, brokerEndPoint, new SystemTime())
-    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsets, endPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
-    val thread = new ReplicaFetcherThread("bob", 0, endPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
     thread.addPartitions(Map(t1p0 -> 0, t1p1 -> 0))
 
     //Loop 1
@@ -174,13 +176,16 @@ class ReplicaFetcherThreadTest {
     val partition = createMock(classOf[Partition])
     val replicaManager = createMock(classOf[ReplicaManager])
 
+    val leaderEpoch = 5
     val initialLEO = 200
 
     //Stubs
     expect(partition.truncateTo(capture(truncateToCapture), anyBoolean())).anyTimes()
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
     expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(initialLEO)).anyTimes()
-    expect(leaderEpochs.latestEpoch).andReturn(5).anyTimes()
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(initialLEO - 1)).anyTimes()
+    expect(leaderEpochs.latestEpoch).andReturn(leaderEpoch).anyTimes()
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, initialLEO)).anyTimes()
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
     stub(replica, partition, replicaManager)
@@ -188,20 +193,208 @@ class ReplicaFetcherThreadTest {
     replay(leaderEpochs, replicaManager, logManager, quota, replica, partition)
 
     //Define the offsets for the OffsetsForLeaderEpochResponse, these are used for truncation
-    val offsetsReply = Map(t1p0 -> new EpochEndOffset(156), t2p1 -> new EpochEndOffset(172)).asJava
+    val offsetsReply = Map(t1p0 -> new EpochEndOffset(leaderEpoch, 156), t2p1 -> new EpochEndOffset(leaderEpoch, 172)).asJava
 
     //Create the thread
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, brokerEndPoint, new SystemTime())
-    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, endPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, configs(0), replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
-    val thread = new ReplicaFetcherThread("bob", 0, endPoint, configs(0), replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
     thread.addPartitions(Map(t1p0 -> 0, t2p1 -> 0))
 
     //Run it
     thread.doWork()
 
     //We should have truncated to the offsets in the response
-    assertTrue(truncateToCapture.getValues.asScala.contains(156))
+    assertTrue("Expected " + t1p0 + " to truncate to offset 156 (truncation offsets: " + truncateToCapture.getValues + ")",
-    assertTrue(truncateToCapture.getValues.asScala.contains(172))
+               truncateToCapture.getValues.asScala.contains(156))
+    assertTrue("Expected " + t2p1 + " to truncate to offset 172 (truncation offsets: " + truncateToCapture.getValues + ")",
+               truncateToCapture.getValues.asScala.contains(172))
+  }
+
+  @Test
+  def shouldTruncateToOffsetSpecifiedInEpochOffsetResponseIfFollowerHasNoMoreEpochs(): Unit = {
+    // Create a capture to track what partitions/offsets are truncated
+    val truncateToCapture: Capture[Long] = newCapture(CaptureType.ALL)
+
+    val config = KafkaConfig.fromProps(TestUtils.createBrokerConfig(1, "localhost:1234"))
+
+    // Setup all the dependencies
+    val configs = TestUtils.createBrokerConfigs(1, "localhost:1234").map(KafkaConfig.fromProps)
+    val quota = createNiceMock(classOf[ReplicationQuotaManager])
+    val leaderEpochs = createMock(classOf[LeaderEpochCache])
+    val logManager = createMock(classOf[LogManager])
+    val replicaAlterLogDirsManager = createMock(classOf[ReplicaAlterLogDirsManager])
+    val replica = createNiceMock(classOf[Replica])
+    val partition = createMock(classOf[Partition])
+    val replicaManager = createMock(classOf[ReplicaManager])
+
+    val leaderEpochAtFollower = 5
+    val leaderEpochAtLeader = 4
+    val initialLEO = 200
+
+    //Stubs
+    expect(partition.truncateTo(capture(truncateToCapture), anyBoolean())).anyTimes()
+    expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
+    expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(initialLEO)).anyTimes()
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(initialLEO - 3)).anyTimes()
+    expect(leaderEpochs.latestEpoch).andReturn(leaderEpochAtFollower).anyTimes()
+    expect(leaderEpochs.endOffsetFor(leaderEpochAtLeader)).andReturn((UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)).anyTimes()
+    expect(replicaManager.logManager).andReturn(logManager).anyTimes()
+    expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
+    stub(replica, partition, replicaManager)
+
+    replay(leaderEpochs, replicaManager, logManager, quota, replica, partition)
+
+    //Define the offsets for the OffsetsForLeaderEpochResponse, these are used for truncation
+    val offsetsReply = Map(t1p0 -> new EpochEndOffset(leaderEpochAtLeader, 156),
+                           t2p1 -> new EpochEndOffset(leaderEpochAtLeader, 202)).asJava
+
+    //Create the thread
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, brokerEndPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, configs(0), replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
+    thread.addPartitions(Map(t1p0 -> 0, t2p1 -> 0))
+
+    //Run it
+    thread.doWork()
+
+    //We should have truncated to the offsets in the response
+    assertTrue("Expected " + t1p0 + " to truncate to offset 156 (truncation offsets: " + truncateToCapture.getValues + ")",
+               truncateToCapture.getValues.asScala.contains(156))
+    assertTrue("Expected " + t2p1 + " to truncate to offset " + initialLEO +
+               " (truncation offsets: " + truncateToCapture.getValues + ")",
+               truncateToCapture.getValues.asScala.contains(initialLEO))
+  }
+
+  @Test
+  def shouldFetchLeaderEpochSecondTimeIfLeaderRepliesWithEpochNotKnownToFollower(): Unit = {
+
+    // Create a capture to track what partitions/offsets are truncated
+    val truncateToCapture: Capture[Long] = newCapture(CaptureType.ALL)
+
+    val config = KafkaConfig.fromProps(TestUtils.createBrokerConfig(1, "localhost:1234"))
+
+    // Setup all dependencies
+    val quota = createNiceMock(classOf[ReplicationQuotaManager])
+    val leaderEpochs = createNiceMock(classOf[LeaderEpochCache])
+    val logManager = createMock(classOf[LogManager])
+    val replicaAlterLogDirsManager = createMock(classOf[ReplicaAlterLogDirsManager])
+    val replica = createNiceMock(classOf[Replica])
+    val partition = createMock(classOf[Partition])
+    val replicaManager = createMock(classOf[ReplicaManager])
+
+    val initialLEO = 200
+
+    // Stubs
+    expect(partition.truncateTo(capture(truncateToCapture), anyBoolean())).anyTimes()
+    expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
+    expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(initialLEO)).anyTimes()
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(initialLEO - 2)).anyTimes()
+    expect(leaderEpochs.latestEpoch).andReturn(5)
+    expect(leaderEpochs.endOffsetFor(4)).andReturn((3, 120)).anyTimes()
+    expect(leaderEpochs.endOffsetFor(3)).andReturn((3, 120)).anyTimes()
+    expect(replicaManager.logManager).andReturn(logManager).anyTimes()
+    expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
+    stub(replica, partition, replicaManager)
+
+    replay(leaderEpochs, replicaManager, logManager, quota, replica, partition)
+
+    // Define the offsets for the OffsetsForLeaderEpochResponse
+    val offsets = Map(t1p0 -> new EpochEndOffset(4, 155), t1p1 -> new EpochEndOffset(4, 143)).asJava
+
+    // Create the fetcher thread
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsets, brokerEndPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
+    thread.addPartitions(Map(t1p0 -> 0, t1p1 -> 0))
+
+    // Loop 1 -- both topic partitions will need to fetch another leader epoch
+    thread.doWork()
+    assertEquals(1, mockNetwork.epochFetchCount)
+    assertEquals(0, mockNetwork.fetchCount)
+
+    // Loop 2 should do the second fetch for both topic partitions because the leader replied with
+    // epoch 4 while follower knows only about epoch 3
+    val nextOffsets = Map(t1p0 -> new EpochEndOffset(3, 101), t1p1 -> new EpochEndOffset(3, 102)).asJava
+    mockNetwork.setOffsetsForNextResponse(nextOffsets)
+    thread.doWork()
+    assertEquals(2, mockNetwork.epochFetchCount)
+    assertEquals(1, mockNetwork.fetchCount)
+    assertEquals("OffsetsForLeaderEpochRequest version.",
+                 1, mockNetwork.lastUsedOffsetForLeaderEpochVersion)
+
+    //Loop 3 we should not fetch epochs
+    thread.doWork()
+    assertEquals(2, mockNetwork.epochFetchCount)
+    assertEquals(2, mockNetwork.fetchCount)
+
+
+    //We should have truncated to the offsets in the second response
+    assertTrue("Expected " + t1p1 + " to truncate to offset 102 (truncation offsets: " + truncateToCapture.getValues + ")",
+               truncateToCapture.getValues.asScala.contains(102))
+    assertTrue("Expected " + t1p0 + " to truncate to offset 101 (truncation offsets: " + truncateToCapture.getValues + ")",
+               truncateToCapture.getValues.asScala.contains(101))
+  }
+
+  @Test
+  def shouldUseLeaderEndOffsetIfInterBrokerVersionBelow20(): Unit = {
+
+    // Create a capture to track what partitions/offsets are truncated
+    val truncateToCapture: Capture[Long] = newCapture(CaptureType.ALL)
+
+    val props = TestUtils.createBrokerConfig(1, "localhost:1234")
+    props.put(KafkaConfig.InterBrokerProtocolVersionProp, "0.11.0")
+    val config = KafkaConfig.fromProps(props)
+
+    // Setup all dependencies
+    val quota = createNiceMock(classOf[ReplicationQuotaManager])
+    val leaderEpochs = createNiceMock(classOf[LeaderEpochCache])
+    val logManager = createMock(classOf[LogManager])
+    val replicaAlterLogDirsManager = createMock(classOf[ReplicaAlterLogDirsManager])
+    val replica = createNiceMock(classOf[Replica])
+    val partition = createMock(classOf[Partition])
+    val replicaManager = createMock(classOf[ReplicaManager])
+
+    val initialLEO = 200
+
+    // Stubs
+    expect(partition.truncateTo(capture(truncateToCapture), anyBoolean())).anyTimes()
+    expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
+    expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(initialLEO)).anyTimes()
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(initialLEO - 2)).anyTimes()
+    expect(leaderEpochs.latestEpoch).andReturn(5)
+    expect(leaderEpochs.endOffsetFor(4)).andReturn((3, 120)).anyTimes()
+    expect(leaderEpochs.endOffsetFor(3)).andReturn((3, 120)).anyTimes()
+    expect(replicaManager.logManager).andReturn(logManager).anyTimes()
+    expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
+    stub(replica, partition, replicaManager)
+
+    replay(leaderEpochs, replicaManager, logManager, quota, replica, partition)
+
+    // Define the offsets for the OffsetsForLeaderEpochResponse with undefined epoch to simulate
+    // older protocol version
+    val offsets = Map(t1p0 -> new EpochEndOffset(EpochEndOffset.UNDEFINED_EPOCH, 155), t1p1 -> new EpochEndOffset(EpochEndOffset.UNDEFINED_EPOCH, 143)).asJava
+
+    // Create the fetcher thread
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsets, brokerEndPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
+    thread.addPartitions(Map(t1p0 -> 0, t1p1 -> 0))
+
+    // Loop 1 -- both topic partitions will truncate to leader offset even though they don't know
+    // about leader epoch
+    thread.doWork()
+    assertEquals(1, mockNetwork.epochFetchCount)
+    assertEquals(1, mockNetwork.fetchCount)
+    assertEquals("OffsetsForLeaderEpochRequest version.",
+                 0, mockNetwork.lastUsedOffsetForLeaderEpochVersion)
+
+    //Loop 2 we should not fetch epochs
+    thread.doWork()
+    assertEquals(1, mockNetwork.epochFetchCount)
+    assertEquals(2, mockNetwork.fetchCount)
+
+    //We should have truncated to the offsets in the first response
+    assertTrue("Expected " + t1p0 + " to truncate to offset 155 (truncation offsets: " + truncateToCapture.getValues + ")",
+               truncateToCapture.getValues.asScala.contains(155))
+    assertTrue("Expected " + t1p1 + " to truncate to offset 143 (truncation offsets: " + truncateToCapture.getValues + ")",
+               truncateToCapture.getValues.asScala.contains(143))
   }
 
   @Test
@@ -227,6 +420,7 @@ class ReplicaFetcherThreadTest {
     expect(partition.truncateTo(capture(truncated), anyBoolean())).anyTimes()
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
     expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(initialLeo)).anyTimes()
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(initialFetchOffset)).anyTimes()
     expect(leaderEpochs.latestEpoch).andReturn(5)
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
@@ -234,18 +428,17 @@ class ReplicaFetcherThreadTest {
     replay(leaderEpochs, replicaManager, logManager, quota, replica, partition)
 
     //Define the offsets for the OffsetsForLeaderEpochResponse, these are used for truncation
-    val offsetsReply = Map(t1p0 -> new EpochEndOffset(EpochEndOffset.UNDEFINED_EPOCH_OFFSET)).asJava
+    val offsetsReply = Map(t1p0 -> new EpochEndOffset(EpochEndOffset.UNDEFINED_EPOCH, EpochEndOffset.UNDEFINED_EPOCH_OFFSET)).asJava
 
     //Create the thread
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, brokerEndPoint, new SystemTime())
-    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, endPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, configs(0), replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
-    val thread = new ReplicaFetcherThread("bob", 0, endPoint, configs(0), replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
     thread.addPartitions(Map(t1p0 -> initialFetchOffset))
 
     //Run it
     thread.doWork()
 
-    //We should have truncated to the highwatermark for partitino 2 only
+    //We should have truncated to initial fetch offset
     assertEquals(initialFetchOffset, truncated.getValue)
   }
 
@@ -265,6 +458,7 @@ class ReplicaFetcherThreadTest {
     val partition = createMock(classOf[Partition])
     val replicaManager = createMock(classOf[kafka.server.ReplicaManager])
 
+    val leaderEpoch = 5
     val highWaterMark = 100
     val initialLeo = 300
 
@@ -273,7 +467,9 @@ class ReplicaFetcherThreadTest {
     expect(partition.truncateTo(capture(truncated), anyBoolean())).anyTimes()
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
     expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(initialLeo)).anyTimes()
-    expect(leaderEpochs.latestEpoch).andReturn(5)
+    expect(leaderEpochs.latestEpoch).andReturn(leaderEpoch)
+    // this is for the last reply with EpochEndOffset(5, 156)
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, initialLeo)).anyTimes()
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
     stub(replica, partition, replicaManager)
@@ -281,14 +477,13 @@ class ReplicaFetcherThreadTest {
 
     //Define the offsets for the OffsetsForLeaderEpochResponse, these are used for truncation
     val offsetsReply = mutable.Map(
-      t1p0 -> new EpochEndOffset(NOT_LEADER_FOR_PARTITION, EpochEndOffset.UNDEFINED_EPOCH_OFFSET),
+      t1p0 -> new EpochEndOffset(NOT_LEADER_FOR_PARTITION, EpochEndOffset.UNDEFINED_EPOCH, EpochEndOffset.UNDEFINED_EPOCH_OFFSET),
-      t1p1 -> new EpochEndOffset(UNKNOWN_SERVER_ERROR, EpochEndOffset.UNDEFINED_EPOCH_OFFSET)
+      t1p1 -> new EpochEndOffset(UNKNOWN_SERVER_ERROR, EpochEndOffset.UNDEFINED_EPOCH, EpochEndOffset.UNDEFINED_EPOCH_OFFSET)
     ).asJava
 
     //Create the thread
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, brokerEndPoint, new SystemTime())
-    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, endPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, configs(0), replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
-    val thread = new ReplicaFetcherThread("bob", 0, endPoint, configs(0), replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
     thread.addPartitions(Map(t1p0 -> 0, t2p1 -> 0))
 
     //Run thread 3 times
@@ -300,7 +495,7 @@ class ReplicaFetcherThreadTest {
     assertEquals(0, truncated.getValues.size())
 
     //New leader elected and replies
-    offsetsReply.put(t1p0, new EpochEndOffset(156))
+    offsetsReply.put(t1p0, new EpochEndOffset(leaderEpoch, 156))
 
     thread.doWork()
 
@@ -321,10 +516,14 @@ class ReplicaFetcherThreadTest {
     val partition = createMock(classOf[Partition])
     val replicaManager = createNiceMock(classOf[ReplicaManager])
 
+    val leaderEpoch = 4
+
     //Stub return values
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
     expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(0)).anyTimes()
-    expect(leaderEpochs.latestEpoch).andReturn(5)
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(0)).anyTimes()
+    expect(leaderEpochs.latestEpoch).andReturn(leaderEpoch)
+    expect(leaderEpochs.endOffsetFor(leaderEpoch)).andReturn((leaderEpoch, 0)).anyTimes()
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
     stub(replica, partition, replicaManager)
@@ -333,13 +532,12 @@ class ReplicaFetcherThreadTest {
 
     //Define the offsets for the OffsetsForLeaderEpochResponse
     val offsetsReply = Map(
-      t1p0 -> new EpochEndOffset(1), t1p1 -> new EpochEndOffset(1)
+      t1p0 -> new EpochEndOffset(leaderEpoch, 1), t1p1 -> new EpochEndOffset(leaderEpoch, 1)
     ).asJava
 
     //Create the fetcher thread
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, brokerEndPoint, new SystemTime())
-    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, endPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
-    val thread = new ReplicaFetcherThread("bob", 0, endPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
 
     //When
     thread.addPartitions(Map(t1p0 -> 0, t1p1 -> 0))
@@ -373,7 +571,9 @@ class ReplicaFetcherThreadTest {
     expect(partition.truncateTo(capture(truncateToCapture), anyBoolean())).once
     expect(replica.epochs).andReturn(Some(leaderEpochs)).anyTimes()
     expect(replica.logEndOffset).andReturn(new LogOffsetMetadata(initialLEO)).anyTimes()
+    expect(replica.highWatermark).andReturn(new LogOffsetMetadata(initialLEO - 2)).anyTimes()
     expect(leaderEpochs.latestEpoch).andReturn(5)
+    expect(leaderEpochs.endOffsetFor(5)).andReturn((5, initialLEO)).anyTimes()
     expect(replicaManager.logManager).andReturn(logManager).anyTimes()
     expect(replicaManager.replicaAlterLogDirsManager).andReturn(replicaAlterLogDirsManager).anyTimes()
     stub(replica, partition, replicaManager)
@@ -382,13 +582,12 @@ class ReplicaFetcherThreadTest {
 
     //Define the offsets for the OffsetsForLeaderEpochResponse
     val offsetsReply = Map(
-      t1p0 -> new EpochEndOffset(52), t1p1 -> new EpochEndOffset(49)
+      t1p0 -> new EpochEndOffset(5, 52), t1p1 -> new EpochEndOffset(5, 49)
     ).asJava
 
     //Create the fetcher thread
-    val endPoint = new BrokerEndPoint(0, "localhost", 1000)
+    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, brokerEndPoint, new SystemTime())
-    val mockNetwork = new ReplicaFetcherMockBlockingSend(offsetsReply, endPoint, new SystemTime())
+    val thread = new ReplicaFetcherThread("bob", 0, brokerEndPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
-    val thread = new ReplicaFetcherThread("bob", 0, endPoint, config, replicaManager, new Metrics(), new SystemTime(), quota, Some(mockNetwork))
 
     //When
     thread.addPartitions(Map(t1p0 -> 0, t1p1 -> 0))

core/src/test/scala/unit/kafka/server/RequestQuotaTest.scala

@@ -258,7 +258,7 @@ class RequestQuotaTest extends BaseRequestTest {
           new InitProducerIdRequest.Builder("abc")
 
         case ApiKeys.OFFSET_FOR_LEADER_EPOCH =>
-          new OffsetsForLeaderEpochRequest.Builder().add(tp, 0)
+          new OffsetsForLeaderEpochRequest.Builder(ApiKeys.OFFSET_FOR_LEADER_EPOCH.latestVersion()).add(tp, 0)
 
         case ApiKeys.ADD_PARTITIONS_TO_TXN =>
           new AddPartitionsToTxnRequest.Builder("test-transactional-id", 1, 0, List(tp).asJava)

core/src/test/scala/unit/kafka/server/epoch/EpochDrivenReplicationProtocolAcceptanceTest.scala

@@ -38,6 +38,7 @@ import org.junit.{After, Before, Test}
 
 import scala.collection.JavaConverters._
 import scala.collection.mutable.{ListBuffer => Buffer}
+import scala.collection.Seq
 
 /**
   * These tests were written to assert the addition of leader epochs to the replication protocol fix the problems
@@ -298,6 +299,86 @@ class EpochDrivenReplicationProtocolAcceptanceTest extends ZooKeeperTestHarness
     }
   }
 
+  @Test
+  def logsShouldNotDivergeOnUncleanLeaderElections(): Unit = {
+
+    // Given two brokers, unclean leader election is enabled
+    brokers = (100 to 101).map(createBroker(_, enableUncleanLeaderElection = true))
+
+    // A single partition topic with 2 replicas, min.isr = 1
+    adminZkClient.createOrUpdateTopicPartitionAssignmentPathInZK(
+      topic, Map(0 -> Seq(100, 101)), config = CoreUtils.propsWith((KafkaConfig.MinInSyncReplicasProp, "1"))
+    )
+    producer = createNewProducer(getBrokerListStrFromServers(brokers), retries = 5, acks = 1)
+
+    // Write one message while both brokers are up
+    (0 until 1).foreach { i =>
+      producer.send(new ProducerRecord(topic, 0, null, msg))
+      producer.flush()}
+
+    // Since we use producer with acks = 1, make sure that logs match for the first epoch
+    waitForLogsToMatch(brokers(0), brokers(1))
+
+    // shutdown broker 100
+    brokers(0).shutdown()
+
+    //Write 1 message
+    (0 until 1).foreach { i =>
+      producer.send(new ProducerRecord(topic, 0, null, msg))
+      producer.flush()}
+
+    brokers(1).shutdown()
+    brokers(0).startup()
+
+    //Bounce the producer (this is required, probably because the broker port changes on restart?)
+    producer.close()
+    producer = createNewProducer(getBrokerListStrFromServers(brokers), retries = 5, acks = 1)
+
+    //Write 3 messages
+    (0 until 3).foreach { i =>
+      producer.send(new ProducerRecord(topic, 0, null, msgBigger))
+      producer.flush()}
+
+    brokers(0).shutdown()
+    brokers(1).startup()
+
+    //Bounce the producer (this is required, probably because the broker port changes on restart?)
+    producer.close()
+    producer = createNewProducer(getBrokerListStrFromServers(brokers), retries = 5, acks = 1)
+
+    //Write 1 message
+    (0 until 1).foreach { i =>
+      producer.send(new ProducerRecord(topic, 0, null, msg))
+      producer.flush()}
+
+    brokers(1).shutdown()
+    brokers(0).startup()
+
+    //Bounce the producer (this is required, probably because the broker port changes on restart?)
+    producer.close()
+    producer = createNewProducer(getBrokerListStrFromServers(brokers), retries = 5, acks = 1)
+
+    //Write 2 messages
+    (0 until 2).foreach { i =>
+      producer.send(new ProducerRecord(topic, 0, null, msgBigger))
+      producer.flush()}
+
+    printSegments()
+
+    brokers(1).startup()
+
+    waitForLogsToMatch(brokers(0), brokers(1))
+    printSegments()
+
+    def crcSeq(broker: KafkaServer, partition: Int = 0): Seq[Long] = {
+      val batches = getLog(broker, partition).activeSegment.read(0, None, Integer.MAX_VALUE)
+        .records.batches().asScala.toSeq
+      batches.map(_.checksum)
+    }
+    assertTrue(s"Logs on Broker 100 and Broker 101 should match",
+               crcSeq(brokers(0)) == crcSeq(brokers(1)))
+  }
+
   private def log(leader: KafkaServer, follower: KafkaServer): Unit = {
     info(s"Bounce complete for follower ${follower.config.brokerId}")
     info(s"Leader: leo${leader.config.brokerId}: " + getLog(leader, 0).logEndOffset + " cache: " + epochCache(leader).epochEntries())
@@ -389,12 +470,13 @@ class EpochDrivenReplicationProtocolAcceptanceTest extends ZooKeeperTestHarness
     brokers.filter(_.config.brokerId != leader)(0)
   }
 
-  private def createBroker(id: Int): KafkaServer = {
+  private def createBroker(id: Int, enableUncleanLeaderElection: Boolean = false): KafkaServer = {
     val config = createBrokerConfig(id, zkConnect)
     if(!KIP_101_ENABLED) {
       config.setProperty(KafkaConfig.InterBrokerProtocolVersionProp, KAFKA_0_11_0_IV1.version)
       config.setProperty(KafkaConfig.LogMessageFormatVersionProp, KAFKA_0_11_0_IV1.version)
     }
+    config.setProperty(KafkaConfig.UncleanLeaderElectionEnableProp, enableUncleanLeaderElection.toString)
     createServer(fromProps(config))
   }
 

core/src/test/scala/unit/kafka/server/epoch/LeaderEpochFileCacheTest.scala

@@ -50,7 +50,7 @@ class LeaderEpochFileCacheTest {
     //Then
     assertEquals(2, cache.latestEpoch())
     assertEquals(EpochEntry(2, 10), cache.epochEntries()(0))
-    assertEquals(11, cache.endOffsetFor(2)) //should match leo
+    assertEquals((2, leo), cache.endOffsetFor(2)) //should match leo
   }
 
   @Test
@@ -67,23 +67,27 @@ class LeaderEpochFileCacheTest {
     leo = 14
 
     //Then
-    assertEquals(14, cache.endOffsetFor(2))
+    assertEquals((2, leo), cache.endOffsetFor(2))
   }
 
   @Test
   def shouldReturnUndefinedOffsetIfUndefinedEpochRequested() = {
     def leoFinder() = new LogOffsetMetadata(0)
+    val expectedEpochEndOffset = (UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET)
 
     //Given cache with some data on leader
     val cache = new LeaderEpochFileCache(tp, () => leoFinder, checkpoint)
+
+    // assign couple of epochs
     cache.assign(epoch = 2, offset = 11)
     cache.assign(epoch = 3, offset = 12)
 
     //When (say a bootstraping follower) sends request for UNDEFINED_EPOCH
-    val offsetFor = cache.endOffsetFor(UNDEFINED_EPOCH)
+    val epochAndOffsetFor = cache.endOffsetFor(UNDEFINED_EPOCH)
 
     //Then
-    assertEquals(UNDEFINED_EPOCH_OFFSET, offsetFor)
+    assertEquals("Expected undefined epoch and offset if undefined epoch requested. Cache not empty.",
+                 expectedEpochEndOffset, epochAndOffsetFor)
   }
 
   @Test
@@ -140,7 +144,7 @@ class LeaderEpochFileCacheTest {
     val cache = new LeaderEpochFileCache(tp, () => leoFinder, checkpoint)
 
     //Then
-    assertEquals(UNDEFINED_EPOCH_OFFSET, cache.endOffsetFor(0))
+    assertEquals((UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET), cache.endOffsetFor(0))
   }
 
   @Test
@@ -155,7 +159,8 @@ class LeaderEpochFileCacheTest {
     val offsetFor = cache.endOffsetFor(UNDEFINED_EPOCH)
 
     //Then
-    assertEquals(UNDEFINED_EPOCH_OFFSET, offsetFor)
+    assertEquals("Expected undefined epoch and offset if undefined epoch requested. Empty cache.",
+                 (UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET), offsetFor)
   }
 
   @Test
@@ -170,10 +175,10 @@ class LeaderEpochFileCacheTest {
     cache.assign(epoch = 7, offset = 13)
 
     //When
-    val offset = cache.endOffsetFor(5 - 1)
+    val epochAndOffset = cache.endOffsetFor(5 - 1)
 
     //Then
-    assertEquals(UNDEFINED_EPOCH_OFFSET, offset)
+    assertEquals((UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET), epochAndOffset)
   }
 
   @Test
@@ -194,7 +199,7 @@ class LeaderEpochFileCacheTest {
     leo = 17
 
     //Then get the start offset of the next epoch
-    assertEquals(15, cache.endOffsetFor(2))
+    assertEquals((2, 15), cache.endOffsetFor(2))
   }
 
   @Test
@@ -210,8 +215,9 @@ class LeaderEpochFileCacheTest {
     cache.assign(epoch = 4, offset = 17)
 
     //Then
-    assertEquals(13, cache.endOffsetFor(requestedEpoch = 1))
+    assertEquals((0, 13), cache.endOffsetFor(requestedEpoch = 1))
-    assertEquals(17, cache.endOffsetFor(requestedEpoch = 2))
+    assertEquals((2, 17), cache.endOffsetFor(requestedEpoch = 2))
+    assertEquals((2, 17), cache.endOffsetFor(requestedEpoch = 3))
   }
 
   @Test
@@ -242,7 +248,7 @@ class LeaderEpochFileCacheTest {
     cache.assign(epoch = 2, offset = 100)
 
     //Then
-    assertEquals(UNDEFINED_EPOCH_OFFSET, cache.endOffsetFor(3))
+    assertEquals((UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET), cache.endOffsetFor(3))
   }
 
   @Test
@@ -258,7 +264,7 @@ class LeaderEpochFileCacheTest {
     leo = 7
 
     //Then
-    assertEquals(leo, cache.endOffsetFor(2))
+    assertEquals((2, leo), cache.endOffsetFor(2))
     assertEquals(1, cache.epochEntries.size)
     assertEquals(EpochEntry(2, 6), cache.epochEntries()(0))
   }
@@ -300,10 +306,10 @@ class LeaderEpochFileCacheTest {
     assertEquals(2, cache.latestEpoch())
 
     //Then end offset for epoch 1 shouldn't have changed
-    assertEquals(6, cache.endOffsetFor(1))
+    assertEquals((1, 6), cache.endOffsetFor(1))
 
-    //Then end offset for epoch 2 has to be the offset of the epoch 1 message (I can't thing of a better option)
+    //Then end offset for epoch 2 has to be the offset of the epoch 1 message (I can't think of a better option)
-    assertEquals(8, cache.endOffsetFor(2))
+    assertEquals((2, 8), cache.endOffsetFor(2))
 
     //Epoch history shouldn't have changed
     assertEquals(EpochEntry(1, 5), cache.epochEntries()(0))
@@ -340,17 +346,17 @@ class LeaderEpochFileCacheTest {
     //Then epoch should go up
     assertEquals(1, cache.latestEpoch())
     //offset for 1 should still be 0
-    assertEquals(0, cache.endOffsetFor(1))
+    assertEquals((1, 0), cache.endOffsetFor(1))
     //offset for epoch 0 should still be 0
-    assertEquals(0, cache.endOffsetFor(0))
+    assertEquals((0, 0), cache.endOffsetFor(0))
 
     //When we write 5 messages as epoch 1
     leo = 5
 
     //Then end offset for epoch(1) should be leo => 5
-    assertEquals(5, cache.endOffsetFor(1))
+    assertEquals((1, 5), cache.endOffsetFor(1))
     //Epoch 0 should still be at offset 0
-    assertEquals(0, cache.endOffsetFor(0))
+    assertEquals((0, 0), cache.endOffsetFor(0))
 
     //When
     cache.assign(epoch = 2, offset = 5) //leo=5
@@ -358,13 +364,13 @@ class LeaderEpochFileCacheTest {
     leo = 10 //write another 5 messages
 
     //Then end offset for epoch(2) should be leo => 10
-    assertEquals(10, cache.endOffsetFor(2))
+    assertEquals((2, 10), cache.endOffsetFor(2))
 
     //end offset for epoch(1) should be the start offset of epoch(2) => 5
-    assertEquals(5, cache.endOffsetFor(1))
+    assertEquals((1, 5), cache.endOffsetFor(1))
 
     //epoch (0) should still be 0
-    assertEquals(0, cache.endOffsetFor(0))
+    assertEquals((0, 0), cache.endOffsetFor(0))
   }
 
   @Test
@@ -382,7 +388,7 @@ class LeaderEpochFileCacheTest {
 
     //Then epoch should stay, offsets should grow
     assertEquals(0, cache.latestEpoch())
-    assertEquals(leo, cache.endOffsetFor(0))
+    assertEquals((0, leo), cache.endOffsetFor(0))
 
     //When messages arrive with greater epoch
     cache.assign(epoch = 1, offset = 3); leo = 4
@@ -390,7 +396,7 @@ class LeaderEpochFileCacheTest {
     cache.assign(epoch = 1, offset = 5); leo = 6
 
     assertEquals(1, cache.latestEpoch())
-    assertEquals(leo, cache.endOffsetFor(1))
+    assertEquals((1, leo), cache.endOffsetFor(1))
 
     //When
     cache.assign(epoch = 2, offset = 6); leo = 7
@@ -398,11 +404,11 @@ class LeaderEpochFileCacheTest {
     cache.assign(epoch = 2, offset = 8); leo = 9
 
     assertEquals(2, cache.latestEpoch())
-    assertEquals(leo, cache.endOffsetFor(2))
+    assertEquals((2, leo), cache.endOffsetFor(2))
 
     //Older epochs should return the start offset of the first message in the subsequent epoch.
-    assertEquals(3, cache.endOffsetFor(0))
+    assertEquals((0, 3), cache.endOffsetFor(0))
-    assertEquals(6, cache.endOffsetFor(1))
+    assertEquals((1, 6), cache.endOffsetFor(1))
   }
 
   @Test
@@ -648,7 +654,7 @@ class LeaderEpochFileCacheTest {
     val cache = new LeaderEpochFileCache(tp, () => leoFinder, checkpoint)
 
     //Then
-    assertEquals(-1, cache.endOffsetFor(7))
+    assertEquals((UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET), cache.endOffsetFor(7))
   }
 
   @Test

core/src/test/scala/unit/kafka/server/epoch/LeaderEpochIntegrationTest.scala

@@ -30,6 +30,7 @@ import org.apache.kafka.common.requests.EpochEndOffset._
 import org.apache.kafka.common.serialization.StringSerializer
 import org.apache.kafka.common.utils.{LogContext, SystemTime}
 import org.apache.kafka.common.TopicPartition
+import org.apache.kafka.common.protocol.ApiKeys
 
 import org.junit.Assert._
 import org.junit.{After, Test}
@@ -265,7 +266,7 @@ class LeaderEpochIntegrationTest extends ZooKeeperTestHarness with Logging {
   private[epoch] class TestFetcherThread(sender: BlockingSend) extends Logging {
 
     def leaderOffsetsFor(partitions: Map[TopicPartition, Int]): Map[TopicPartition, EpochEndOffset] = {
-      val request = new OffsetsForLeaderEpochRequest.Builder(toJavaFormat(partitions))
+      val request = new OffsetsForLeaderEpochRequest.Builder(ApiKeys.OFFSET_FOR_LEADER_EPOCH.latestVersion(), toJavaFormat(partitions))
       val response = sender.sendRequest(request)
       response.responseBody.asInstanceOf[OffsetsForLeaderEpochResponse].responses.asScala
     }

core/src/test/scala/unit/kafka/server/epoch/OffsetsForLeaderEpochTest.scala

@@ -41,7 +41,7 @@ class OffsetsForLeaderEpochTest {
   @Test
   def shouldGetEpochsFromReplica(): Unit = {
     //Given
-    val offset = 42
+    val epochAndOffset = (5, 42L)
     val epochRequested: Integer = 5
     val request = Map(tp -> epochRequested)
 
@@ -49,7 +49,7 @@ class OffsetsForLeaderEpochTest {
     val mockLog = createNiceMock(classOf[kafka.log.Log])
     val mockCache = createNiceMock(classOf[kafka.server.epoch.LeaderEpochCache])
     val logManager = createNiceMock(classOf[kafka.log.LogManager])
-    expect(mockCache.endOffsetFor(epochRequested)).andReturn(offset)
+    expect(mockCache.endOffsetFor(epochRequested)).andReturn(epochAndOffset)
     expect(mockLog.leaderEpochCache).andReturn(mockCache).anyTimes()
     expect(logManager.liveLogDirs).andReturn(Array.empty[File]).anyTimes()
     replay(mockCache, mockLog, logManager)
@@ -67,7 +67,7 @@ class OffsetsForLeaderEpochTest {
     val response = replicaManager.lastOffsetForLeaderEpoch(request)
 
     //Then
-    assertEquals(new EpochEndOffset(Errors.NONE, offset), response(tp))
+    assertEquals(new EpochEndOffset(Errors.NONE, epochAndOffset._1, epochAndOffset._2), response(tp))
   }
 
   @Test
@@ -90,7 +90,7 @@ class OffsetsForLeaderEpochTest {
     val response = replicaManager.lastOffsetForLeaderEpoch(request)
 
     //Then
-    assertEquals(new EpochEndOffset(Errors.NOT_LEADER_FOR_PARTITION, UNDEFINED_EPOCH_OFFSET), response(tp))
+    assertEquals(new EpochEndOffset(Errors.NOT_LEADER_FOR_PARTITION, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET), response(tp))
   }
 
   @Test
@@ -112,6 +112,6 @@ class OffsetsForLeaderEpochTest {
     val response = replicaManager.lastOffsetForLeaderEpoch(request)
 
     //Then
-    assertEquals(new EpochEndOffset(Errors.UNKNOWN_TOPIC_OR_PARTITION, UNDEFINED_EPOCH_OFFSET), response(tp))
+    assertEquals(new EpochEndOffset(Errors.UNKNOWN_TOPIC_OR_PARTITION, UNDEFINED_EPOCH, UNDEFINED_EPOCH_OFFSET), response(tp))
   }
 }

core/src/test/scala/unit/kafka/server/epoch/util/ReplicaFetcherMockBlockingSend.scala

@@ -28,17 +28,28 @@ import org.apache.kafka.common.utils.{SystemTime, Time}
 
 /**
   * Stub network client used for testing the ReplicaFetcher, wraps the MockClient used for consumer testing
+  *
+  * The common case is that there is only one OFFSET_FOR_LEADER_EPOCH request/response. So, the
+  * response to OFFSET_FOR_LEADER_EPOCH is 'offsets' map. If the test needs to set another round of
+  * OFFSET_FOR_LEADER_EPOCH with different offsets in response, it should update offsets using
+  * setOffsetsForNextResponse
   */
 class ReplicaFetcherMockBlockingSend(offsets: java.util.Map[TopicPartition, EpochEndOffset], destination: BrokerEndPoint, time: Time) extends BlockingSend {
   private val client = new MockClient(new SystemTime)
   var fetchCount = 0
   var epochFetchCount = 0
+  var lastUsedOffsetForLeaderEpochVersion = -1
   var callback: Option[() => Unit] = None
+  var currentOffsets: java.util.Map[TopicPartition, EpochEndOffset] = offsets
 
   def setEpochRequestCallback(postEpochFunction: () => Unit){
     callback = Some(postEpochFunction)
   }
 
+  def setOffsetsForNextResponse(newOffsets: java.util.Map[TopicPartition, EpochEndOffset]): Unit = {
+    currentOffsets = newOffsets
+  }
+
   override def sendRequest(requestBuilder: Builder[_ <: AbstractRequest]): ClientResponse = {
 
     //Send the request to the mock client
@@ -50,7 +61,8 @@ class ReplicaFetcherMockBlockingSend(offsets: java.util.Map[TopicPartition, Epoc
       case ApiKeys.OFFSET_FOR_LEADER_EPOCH =>
         callback.foreach(_.apply())
         epochFetchCount += 1
-        new OffsetsForLeaderEpochResponse(offsets)
+        lastUsedOffsetForLeaderEpochVersion = requestBuilder.latestAllowedVersion()
+        new OffsetsForLeaderEpochResponse(currentOffsets)
 
       case ApiKeys.FETCH =>
         fetchCount += 1

docs/upgrade.html

@@ -19,6 +19,58 @@
 
 <script id="upgrade-template" type="text/x-handlebars-template">
 
+<h4><a id="upgrade_2_0_0" href="#upgrade_2_0_0">Upgrading from 0.8.x, 0.9.x, 0.10.0.x, 0.10.1.x, 0.10.2.x, 0.11.0.x, 1.0.x, 1.1.x, or 1.2.x to 2.0.0</a></h4>
+<p>Kafka 2.0.0 introduces wire protocol changes. By following the recommended rolling upgrade plan below,
+    you guarantee no downtime during the upgrade. However, please review the <a href="#upgrade_200_notable">notable changes in 2.0.0</a> before upgrading.
+</p>
+
+<p><b>For a rolling upgrade:</b></p>
+
+<ol>
+    <li> Update server.properties on all brokers and add the following properties. CURRENT_KAFKA_VERSION refers to the version you
+        are upgrading from. CURRENT_MESSAGE_FORMAT_VERSION refers to the message format version currently in use. If you have previously
+        overridden the message format version, you should keep its current value. Alternatively, if you are upgrading from a version prior
+        to 0.11.0.x, then CURRENT_MESSAGE_FORMAT_VERSION should be set to match CURRENT_KAFKA_VERSION.
+        <ul>
+            <li>inter.broker.protocol.version=CURRENT_KAFKA_VERSION (e.g. 0.8.2, 0.9.0, 0.10.0, 0.10.1, 0.10.2, 0.11.0, 1.0, 1.1, 1.2).</li>
+            <li>log.message.format.version=CURRENT_MESSAGE_FORMAT_VERSION  (See <a href="#upgrade_10_performance_impact">potential performance impact
+                following the upgrade</a> for the details on what this configuration does.)</li>
+        </ul>
+        If you are upgrading from 0.11.0.x, 1.0.x, 1.1.x or 1.2.x and you have not overridden the message format, then you only need to override
+        the inter-broker protocol format.
+        <ul>
+            <li>inter.broker.protocol.version=CURRENT_KAFKA_VERSION (0.11.0, 1.0, 1.1, 1.2).</li>
+        </ul>
+    </li>
+    <li> Upgrade the brokers one at a time: shut down the broker, update the code, and restart it. </li>
+    <li> Once the entire cluster is upgraded, bump the protocol version by editing <code>inter.broker.protocol.version</code> and setting it to 2.0.
+    <li> Restart the brokers one by one for the new protocol version to take effect.</li>
+    <li> If you have overridden the message format version as instructed above, then you need to do one more rolling restart to
+        upgrade it to its latest version. Once all (or most) consumers have been upgraded to 0.11.0 or later,
+        change log.message.format.version to 2.0 on each broker and restart them one by one. Note that the older Scala consumer
+        does not support the new message format introduced in 0.11, so to avoid the performance cost of down-conversion (or to
+        take advantage of <a href="#upgrade_11_exactly_once_semantics">exactly once semantics</a>), the newer Java consumer must be used.</li>
+</ol>
+
+<p><b>Additional Upgrade Notes:</b></p>
+
+<ol>
+    <li>If you are willing to accept downtime, you can simply take all the brokers down, update the code and start them back up. They will start
+        with the new protocol by default.</li>
+    <li>Bumping the protocol version and restarting can be done any time after the brokers are upgraded. It does not have to be immediately after.
+        Similarly for the message format version.</li>
+    <li>If you are using Java8 method references in your Kafka Streams code you might need to update your code to resolve method ambiguties.
+        Hot-swaping the jar-file only might not work.</li>
+</ol>
+
+<h5><a id="upgrade_200_notable" href="#upgrade_200_notable">Notable changes in 2.0.0</a></h5>
+<ul>
+</ul>
+
+<h5><a id="upgrade_200_new_protocols" href="#upgrade_200_new_protocols">New Protocol Versions</a></h5>
+<ul>
+    <li> <a href="https://cwiki.apache.org/confluence/display/KAFKA/KIP-279%3A+Fix+log+divergence+between+leader+and+follower+after+fast+leader+fail+over">KIP-279</a>: OffsetsForLeaderEpochResponse v1 introduces a partition-level <code>leader_epoch</code> field. </li>
+</ul>
 
 <h4><a id="upgrade_2_0_0" href="#upgrade_2_0_0">Upgrading from 0.8.x, 0.9.x, 0.10.0.x, 0.10.1.x, 0.10.2.x, 0.11.0.x, 1.0.x, or 1.1.x to 2.0.x</a></h4>
 <p>Kafka 2.0.0 introduces wire protocol changes. By following the recommended rolling upgrade plan below,