ProducerStateManager.scala

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package kafka.log

import java.io._
import java.nio.ByteBuffer
import java.nio.file.Files

import kafka.common.KafkaException
import kafka.log.Log.offsetFromFilename
import kafka.server.LogOffsetMetadata
import kafka.utils.{Logging, nonthreadsafe, threadsafe}
import org.apache.kafka.common.TopicPartition
import org.apache.kafka.common.errors._
import org.apache.kafka.common.internals.Topic
import org.apache.kafka.common.protocol.types._
import org.apache.kafka.common.record.{ControlRecordType, EndTransactionMarker, RecordBatch}
import org.apache.kafka.common.utils.{ByteUtils, Crc32C}

import scala.collection.mutable.ListBuffer
import scala.collection.{immutable, mutable}

class CorruptSnapshotException(msg: String) extends KafkaException(msg)

private[log] case class TxnMetadata(producerId: Long, var firstOffset: LogOffsetMetadata, var lastOffset: Option[Long] = None) {
  def this(producerId: Long, firstOffset: Long) = this(producerId, LogOffsetMetadata(firstOffset))

  override def toString: String = {
    "TxnMetadata(" +
      s"producerId=$producerId, " +
      s"firstOffset=$firstOffset, " +
      s"lastOffset=$lastOffset)"
  }
}

private[log] object ProducerIdEntry {
  val Empty = ProducerIdEntry(RecordBatch.NO_PRODUCER_ID, RecordBatch.NO_PRODUCER_EPOCH, RecordBatch.NO_SEQUENCE,
    -1, 0, RecordBatch.NO_TIMESTAMP, -1, None)
}

private[log] case class ProducerIdEntry(producerId: Long, producerEpoch: Short, lastSeq: Int, lastOffset: Long,
                                        offsetDelta: Int, timestamp: Long, coordinatorEpoch: Int,
                                        currentTxnFirstOffset: Option[Long]) {
  def firstSeq: Int = lastSeq - offsetDelta
  def firstOffset: Long = lastOffset - offsetDelta

  def isDuplicate(batch: RecordBatch): Boolean = {
    batch.producerEpoch == producerEpoch &&
      batch.baseSequence == firstSeq &&
      batch.lastSequence == lastSeq
  }

  override def toString: String = {
    "ProducerIdEntry(" +
      s"producerId=$producerId, " +
      s"producerEpoch=$producerEpoch, " +
      s"firstSequence=$firstSeq, " +
      s"lastSequence=$lastSeq, " +
      s"firstOffset=$firstOffset, " +
      s"lastOffset=$lastOffset, " +
      s"timestamp=$timestamp, " +
      s"currentTxnFirstOffset=$currentTxnFirstOffset, " +
      s"coordinatorEpoch=$coordinatorEpoch)"
  }
}

/**
 * This class is used to validate the records appended by a given producer before they are written to the log.
 * It is initialized with the producer's state after the last successful append, and transitively validates the
 * sequence numbers and epochs of each new record. Additionally, this class accumulates transaction metadata
 * as the incoming records are validated.
 *
 * @param producerId The id of the producer appending to the log
 * @param initialEntry The last entry associated with the producer id. Validation of the first append will be
 *                     based off of this entry initially
 * @param validateSequenceNumbers Whether or not sequence numbers should be validated. The only current use
 *                                of this is the consumer offsets topic which uses producer ids from incoming
 *                                TxnOffsetCommit, but has no sequence number to validate and does not depend
 *                                on the deduplication which sequence numbers provide.
 * @param loadingFromLog This parameter indicates whether the new append is being loaded directly from the log.
 *                       This is used to repopulate producer state when the broker is initialized. The only
 *                       difference in behavior is that we do not validate the sequence number of the first append
 *                       since we may have lost previous sequence numbers when segments were removed due to log
 *                       retention enforcement.
 */
private[log] class ProducerAppendInfo(val producerId: Long,
                                      initialEntry: ProducerIdEntry,
                                      validateSequenceNumbers: Boolean,
                                      loadingFromLog: Boolean) {
  private var producerEpoch = initialEntry.producerEpoch
  private var firstSeq = initialEntry.firstSeq
  private var lastSeq = initialEntry.lastSeq
  private var lastOffset = initialEntry.lastOffset
  private var maxTimestamp = initialEntry.timestamp
  private var currentTxnFirstOffset = initialEntry.currentTxnFirstOffset
  private var coordinatorEpoch = initialEntry.coordinatorEpoch
  private val transactions = ListBuffer.empty[TxnMetadata]

  private def validateAppend(producerEpoch: Short, firstSeq: Int, lastSeq: Int) = {
    if (isFenced(producerEpoch)) {
      throw new ProducerFencedException(s"Producer's epoch is no longer valid. There is probably another producer " +
        s"with a newer epoch. $producerEpoch (request epoch), ${this.producerEpoch} (server epoch)")
    } else if (validateSequenceNumbers) {
      if (producerEpoch != this.producerEpoch) {
        if (firstSeq != 0)
          throw new OutOfOrderSequenceException(s"Invalid sequence number for new epoch: $producerEpoch " +
            s"(request epoch), $firstSeq (seq. number)")
      } else if (this.firstSeq == RecordBatch.NO_SEQUENCE && firstSeq != 0) {
        // the epoch was bumped by a control record, so we expect the sequence number to be reset
        throw new OutOfOrderSequenceException(s"Out of order sequence number for producerId $producerId: found $firstSeq " +
          s"(incoming seq. number), but expected 0")
      } else if (firstSeq == this.firstSeq && lastSeq == this.lastSeq) {
        throw new DuplicateSequenceNumberException(s"Duplicate sequence number for producerId $producerId: (incomingBatch.firstSeq, " +
          s"incomingBatch.lastSeq): ($firstSeq, $lastSeq), (lastEntry.firstSeq, lastEntry.lastSeq): " +
          s"(${this.firstSeq}, ${this.lastSeq}).")
      } else if (!inSequence(firstSeq, lastSeq)) {
        throw new OutOfOrderSequenceException(s"Out of order sequence number for producerId $producerId: $firstSeq " +
          s"(incoming seq. number), ${this.lastSeq} (current end sequence number)")
      }
    }
  }

  private def inSequence(firstSeq: Int, lastSeq: Int): Boolean = {
    firstSeq == this.lastSeq + 1L || (firstSeq == 0 && this.lastSeq == Int.MaxValue)
  }

  private def isFenced(producerEpoch: Short): Boolean = {
    producerEpoch < this.producerEpoch
  }

  def append(batch: RecordBatch): Option[CompletedTxn] = {
    if (batch.isControlBatch) {
      val record = batch.iterator.next()
      val endTxnMarker = EndTransactionMarker.deserialize(record)
      val completedTxn = appendEndTxnMarker(endTxnMarker, batch.producerEpoch, batch.baseOffset, record.timestamp)
      Some(completedTxn)
    } else {
      append(batch.producerEpoch, batch.baseSequence, batch.lastSequence, batch.maxTimestamp, batch.lastOffset,
        batch.isTransactional)
      None
    }
  }

  def append(epoch: Short,
             firstSeq: Int,
             lastSeq: Int,
             lastTimestamp: Long,
             lastOffset: Long,
             isTransactional: Boolean): Unit = {
    if (epoch != RecordBatch.NO_PRODUCER_EPOCH && !loadingFromLog)
      // skip validation if this is the first entry when loading from the log. Log retention
      // will generally have removed the beginning entries from each producer id
      validateAppend(epoch, firstSeq, lastSeq)

    this.producerEpoch = epoch
    this.firstSeq = firstSeq
    this.lastSeq = lastSeq
    this.maxTimestamp = lastTimestamp
    this.lastOffset = lastOffset

    if (currentTxnFirstOffset.isDefined && !isTransactional)
      throw new InvalidTxnStateException(s"Expected transactional write from producer $producerId")

    if (isTransactional && currentTxnFirstOffset.isEmpty) {
      val firstOffset = lastOffset - (lastSeq - firstSeq)
      currentTxnFirstOffset = Some(firstOffset)
      transactions += new TxnMetadata(producerId, firstOffset)
    }
  }

  def appendEndTxnMarker(endTxnMarker: EndTransactionMarker,
                         producerEpoch: Short,
                         offset: Long,
                         timestamp: Long): CompletedTxn = {
    if (isFenced(producerEpoch))
      throw new ProducerFencedException(s"Invalid producer epoch: $producerEpoch (zombie): ${this.producerEpoch} (current)")

    if (this.coordinatorEpoch > endTxnMarker.coordinatorEpoch)
      throw new TransactionCoordinatorFencedException(s"Invalid coordinator epoch: ${endTxnMarker.coordinatorEpoch} " +
        s"(zombie), $coordinatorEpoch (current)")

    if (producerEpoch != this.producerEpoch) {
      // it is possible that this control record is the first record seen from a new epoch (the producer
      // may fail before sending to the partition or the request itself could fail for some reason). In this
      // case, we bump the epoch and reset the sequence numbers
      this.producerEpoch = producerEpoch
      this.firstSeq = RecordBatch.NO_SEQUENCE
      this.lastSeq = RecordBatch.NO_SEQUENCE
    } else {
      // the control record is the last append to the log, so the last offset will be updated to point to it.
      // However, the sequence numbers still point to the previous batch, so the duplicate check would no longer
      // be correct: it would return the wrong offset. To fix this, we treat the control record as a batch
      // of size 1 which uses the last appended sequence number.
      this.firstSeq = this.lastSeq
    }

    val firstOffset = currentTxnFirstOffset match {
      case Some(txnFirstOffset) => txnFirstOffset
      case None =>
        transactions += new TxnMetadata(producerId, offset)
        offset
    }

    this.lastOffset = offset
    this.currentTxnFirstOffset = None
    this.maxTimestamp = timestamp
    this.coordinatorEpoch = endTxnMarker.coordinatorEpoch
    CompletedTxn(producerId, firstOffset, offset, endTxnMarker.controlType == ControlRecordType.ABORT)
  }

  def lastEntry: ProducerIdEntry =
    ProducerIdEntry(producerId, producerEpoch, lastSeq, lastOffset, lastSeq - firstSeq, maxTimestamp,
      coordinatorEpoch, currentTxnFirstOffset)

  def startedTransactions: List[TxnMetadata] = transactions.toList

  def maybeCacheTxnFirstOffsetMetadata(logOffsetMetadata: LogOffsetMetadata): Unit = {
    // we will cache the log offset metadata if it corresponds to the starting offset of
    // the last transaction that was started. This is optimized for leader appends where it
    // is only possible to have one transaction started for each log append, and the log
    // offset metadata will always match in that case since no data from other producers
    // is mixed into the append
    transactions.headOption.foreach { txn =>
      if (txn.firstOffset.messageOffset == logOffsetMetadata.messageOffset)
        txn.firstOffset = logOffsetMetadata
    }
  }

  override def toString: String = {
    "ProducerAppendInfo(" +
      s"producerId=$producerId, " +
      s"producerEpoch=$producerEpoch, " +
      s"firstSequence=$firstSeq, " +
      s"lastSequence=$lastSeq, " +
      s"currentTxnFirstOffset=$currentTxnFirstOffset, " +
      s"coordinatorEpoch=$coordinatorEpoch, " +
      s"startedTransactions=$transactions)"
  }
}

object ProducerStateManager {
  private val ProducerSnapshotVersion: Short = 1
  private val VersionField = "version"
  private val CrcField = "crc"
  private val ProducerIdField = "producer_id"
  private val LastSequenceField = "last_sequence"
  private val ProducerEpochField = "epoch"
  private val LastOffsetField = "last_offset"
  private val OffsetDeltaField = "offset_delta"
  private val TimestampField = "timestamp"
  private val ProducerEntriesField = "producer_entries"
  private val CoordinatorEpochField = "coordinator_epoch"
  private val CurrentTxnFirstOffsetField = "current_txn_first_offset"

  private val VersionOffset = 0
  private val CrcOffset = VersionOffset + 2
  private val ProducerEntriesOffset = CrcOffset + 4

  val ProducerSnapshotEntrySchema = new Schema(
    new Field(ProducerIdField, Type.INT64, "The producer ID"),
    new Field(ProducerEpochField, Type.INT16, "Current epoch of the producer"),
    new Field(LastSequenceField, Type.INT32, "Last written sequence of the producer"),
    new Field(LastOffsetField, Type.INT64, "Last written offset of the producer"),
    new Field(OffsetDeltaField, Type.INT32, "The difference of the last sequence and first sequence in the last written batch"),
    new Field(TimestampField, Type.INT64, "Max timestamp from the last written entry"),
    new Field(CoordinatorEpochField, Type.INT32, "The epoch of the last transaction coordinator to send an end transaction marker"),
    new Field(CurrentTxnFirstOffsetField, Type.INT64, "The first offset of the on-going transaction (-1 if there is none)"))
  val PidSnapshotMapSchema = new Schema(
    new Field(VersionField, Type.INT16, "Version of the snapshot file"),
    new Field(CrcField, Type.UNSIGNED_INT32, "CRC of the snapshot data"),
    new Field(ProducerEntriesField, new ArrayOf(ProducerSnapshotEntrySchema), "The entries in the producer table"))

  def readSnapshot(file: File): Iterable[ProducerIdEntry] = {
    try {
      val buffer = Files.readAllBytes(file.toPath)
      val struct = PidSnapshotMapSchema.read(ByteBuffer.wrap(buffer))

      val version = struct.getShort(VersionField)
      if (version != ProducerSnapshotVersion)
        throw new CorruptSnapshotException(s"Snapshot contained an unknown file version $version")

      val crc = struct.getUnsignedInt(CrcField)
      val computedCrc =  Crc32C.compute(buffer, ProducerEntriesOffset, buffer.length - ProducerEntriesOffset)
      if (crc != computedCrc)
        throw new CorruptSnapshotException(s"Snapshot is corrupt (CRC is no longer valid). " +
          s"Stored crc: $crc. Computed crc: $computedCrc")

      struct.getArray(ProducerEntriesField).map { producerEntryObj =>
        val producerEntryStruct = producerEntryObj.asInstanceOf[Struct]
        val producerId: Long = producerEntryStruct.getLong(ProducerIdField)
        val producerEpoch = producerEntryStruct.getShort(ProducerEpochField)
        val seq = producerEntryStruct.getInt(LastSequenceField)
        val offset = producerEntryStruct.getLong(LastOffsetField)
        val timestamp = producerEntryStruct.getLong(TimestampField)
        val offsetDelta = producerEntryStruct.getInt(OffsetDeltaField)
        val coordinatorEpoch = producerEntryStruct.getInt(CoordinatorEpochField)
        val currentTxnFirstOffset = producerEntryStruct.getLong(CurrentTxnFirstOffsetField)
        val newEntry = ProducerIdEntry(producerId, producerEpoch, seq, offset, offsetDelta, timestamp,
          coordinatorEpoch, if (currentTxnFirstOffset >= 0) Some(currentTxnFirstOffset) else None)
        newEntry
      }
    } catch {
      case e: SchemaException =>
        throw new CorruptSnapshotException(s"Snapshot failed schema validation: ${e.getMessage}")
    }
  }

  private def writeSnapshot(file: File, entries: mutable.Map[Long, ProducerIdEntry]) {
    val struct = new Struct(PidSnapshotMapSchema)
    struct.set(VersionField, ProducerSnapshotVersion)
    struct.set(CrcField, 0L) // we'll fill this after writing the entries
    val entriesArray = entries.map {
      case (producerId, entry) =>
        val producerEntryStruct = struct.instance(ProducerEntriesField)
        producerEntryStruct.set(ProducerIdField, producerId)
          .set(ProducerEpochField, entry.producerEpoch)
          .set(LastSequenceField, entry.lastSeq)
          .set(LastOffsetField, entry.lastOffset)
          .set(OffsetDeltaField, entry.offsetDelta)
          .set(TimestampField, entry.timestamp)
          .set(CoordinatorEpochField, entry.coordinatorEpoch)
          .set(CurrentTxnFirstOffsetField, entry.currentTxnFirstOffset.getOrElse(-1L))
        producerEntryStruct
    }.toArray
    struct.set(ProducerEntriesField, entriesArray)

    val buffer = ByteBuffer.allocate(struct.sizeOf)
    struct.writeTo(buffer)
    buffer.flip()

    // now fill in the CRC
    val crc = Crc32C.compute(buffer, ProducerEntriesOffset, buffer.limit - ProducerEntriesOffset)
    ByteUtils.writeUnsignedInt(buffer, CrcOffset, crc)

    val fos = new FileOutputStream(file)
    try {
      fos.write(buffer.array, buffer.arrayOffset, buffer.limit)
    } finally {
      fos.close()
    }
  }

  private def isSnapshotFile(name: String): Boolean = name.endsWith(Log.PidSnapshotFileSuffix)

}

/**
 * Maintains a mapping from ProducerIds to metadata about the last appended entries (e.g.
 * epoch, sequence number, last offset, etc.)
 *
 * The sequence number is the last number successfully appended to the partition for the given identifier.
 * The epoch is used for fencing against zombie writers. The offset is the one of the last successful message
 * appended to the partition.
 *
 * As long as a producer id is contained in the map, the corresponding producer can continue to write data.
 * However, producer ids can be expired due to lack of recent use or if the last written entry has been deleted from
 * the log (e.g. if the retention policy is "delete"). For compacted topics, the log cleaner will ensure
 * that the most recent entry from a given producer id is retained in the log provided it hasn't expired due to
 * age. This ensures that producer ids will not be expired until either the max expiration time has been reached,
 * or if the topic also is configured for deletion, the segment containing the last written offset has
 * been deleted.
 */
@nonthreadsafe
class ProducerStateManager(val topicPartition: TopicPartition,
                           val logDir: File,
                           val maxProducerIdExpirationMs: Int = 60 * 60 * 1000) extends Logging {
  import ProducerStateManager._
  import java.util

  private val validateSequenceNumbers = topicPartition.topic != Topic.GROUP_METADATA_TOPIC_NAME
  private val producers = mutable.Map.empty[Long, ProducerIdEntry]
  private var lastMapOffset = 0L
  private var lastSnapOffset = 0L

  // ongoing transactions sorted by the first offset of the transaction
  private val ongoingTxns = new util.TreeMap[Long, TxnMetadata]

  // completed transactions whose markers are at offsets above the high watermark
  private val unreplicatedTxns = new util.TreeMap[Long, TxnMetadata]

  /**
   * An unstable offset is one which is either undecided (i.e. its ultimate outcome is not yet known),
   * or one that is decided, but may not have been replicated (i.e. any transaction which has a COMMIT/ABORT
   * marker written at a higher offset than the current high watermark).
   */
  def firstUnstableOffset: Option[LogOffsetMetadata] = {
    val unreplicatedFirstOffset = Option(unreplicatedTxns.firstEntry).map(_.getValue.firstOffset)
    val undecidedFirstOffset = Option(ongoingTxns.firstEntry).map(_.getValue.firstOffset)
    if (unreplicatedFirstOffset.isEmpty)
      undecidedFirstOffset
    else if (undecidedFirstOffset.isEmpty)
      unreplicatedFirstOffset
    else if (undecidedFirstOffset.get.messageOffset < unreplicatedFirstOffset.get.messageOffset)
      undecidedFirstOffset
    else
      unreplicatedFirstOffset
  }

  /**
   * Acknowledge all transactions which have been completed before a given offset. This allows the LSO
   * to advance to the next unstable offset.
   */
  def onHighWatermarkUpdated(highWatermark: Long): Unit = {
    removeUnreplicatedTransactions(highWatermark)
  }

  /**
   * The first undecided offset is the earliest transactional message which has not yet been committed
   * or aborted.
   */
  def firstUndecidedOffset: Option[Long] = Option(ongoingTxns.firstEntry).map(_.getValue.firstOffset.messageOffset)

  /**
   * Returns the last offset of this map
   */
  def mapEndOffset = lastMapOffset

  /**
   * Get a copy of the active producers
   */
  def activeProducers: immutable.Map[Long, ProducerIdEntry] = producers.toMap

  def isEmpty: Boolean = producers.isEmpty && unreplicatedTxns.isEmpty

  private def loadFromSnapshot(logStartOffset: Long, currentTime: Long) {
    while (true) {
      latestSnapshotFile match {
        case Some(file) =>
          try {
            info(s"Loading producer state from snapshot file '$file' for partition $topicPartition")
            val loadedProducers = readSnapshot(file).filter { producerEntry =>
              isProducerRetained(producerEntry, logStartOffset) && !isProducerExpired(currentTime, producerEntry)
            }
            loadedProducers.foreach(loadProducerEntry)
            lastSnapOffset = offsetFromFilename(file.getName)
            lastMapOffset = lastSnapOffset
            return
          } catch {
            case e: CorruptSnapshotException =>
              warn(s"Failed to load producer snapshot from '$file': ${e.getMessage}")
              Files.deleteIfExists(file.toPath)
          }
        case None =>
          lastSnapOffset = logStartOffset
          lastMapOffset = logStartOffset
          return
      }
    }
  }

  // visible for testing
  private[log] def loadProducerEntry(entry: ProducerIdEntry): Unit = {
    val producerId = entry.producerId
    producers.put(producerId, entry)
    entry.currentTxnFirstOffset.foreach { offset =>
      ongoingTxns.put(offset, new TxnMetadata(producerId, offset))
    }
  }

  private def isProducerExpired(currentTimeMs: Long, producerIdEntry: ProducerIdEntry): Boolean =
    producerIdEntry.currentTxnFirstOffset.isEmpty && currentTimeMs - producerIdEntry.timestamp >= maxProducerIdExpirationMs

  /**
   * Expire any producer ids which have been idle longer than the configured maximum expiration timeout.
   */
  def removeExpiredProducers(currentTimeMs: Long) {
    producers.retain { case (producerId, lastEntry) =>
      !isProducerExpired(currentTimeMs, lastEntry)
    }
  }

  /**
   * Truncate the producer id mapping to the given offset range and reload the entries from the most recent
   * snapshot in range (if there is one). Note that the log end offset is assumed to be less than
   * or equal to the high watermark.
   */
  def truncateAndReload(logStartOffset: Long, logEndOffset: Long, currentTimeMs: Long) {
    // remove all out of range snapshots
    deleteSnapshotFiles { snapOffset =>
      snapOffset > logEndOffset || snapOffset <= logStartOffset
    }

    if (logEndOffset != mapEndOffset) {
      producers.clear()
      ongoingTxns.clear()

      // since we assume that the offset is less than or equal to the high watermark, it is
      // safe to clear the unreplicated transactions
      unreplicatedTxns.clear()
      loadFromSnapshot(logStartOffset, currentTimeMs)
    } else {
      truncateHead(logStartOffset)
    }
  }

  def prepareUpdate(producerId: Long, loadingFromLog: Boolean): ProducerAppendInfo =
    new ProducerAppendInfo(producerId, lastEntry(producerId).getOrElse(ProducerIdEntry.Empty), validateSequenceNumbers,
      loadingFromLog)

  /**
   * Update the mapping with the given append information
   */
  def update(appendInfo: ProducerAppendInfo): Unit = {
    if (appendInfo.producerId == RecordBatch.NO_PRODUCER_ID)
      throw new IllegalArgumentException(s"Invalid producer id ${appendInfo.producerId} passed to update")

    trace(s"Updated producer ${appendInfo.producerId} state to $appendInfo")

    val entry = appendInfo.lastEntry
    producers.put(appendInfo.producerId, entry)
    appendInfo.startedTransactions.foreach { txn =>
      ongoingTxns.put(txn.firstOffset.messageOffset, txn)
    }
  }

  def updateMapEndOffset(lastOffset: Long): Unit = {
    lastMapOffset = lastOffset
  }

  /**
   * Get the last written entry for the given producer id.
   */
  def lastEntry(producerId: Long): Option[ProducerIdEntry] = producers.get(producerId)

  /**
   * Take a snapshot at the current end offset if one does not already exist.
   */
  def takeSnapshot(): Unit = {
    // If not a new offset, then it is not worth taking another snapshot
    if (lastMapOffset > lastSnapOffset) {
      val snapshotFile = Log.producerSnapshotFile(logDir, lastMapOffset)
      debug(s"Writing producer snapshot for partition $topicPartition at offset $lastMapOffset")
      writeSnapshot(snapshotFile, producers)

      // Update the last snap offset according to the serialized map
      lastSnapOffset = lastMapOffset
    }
  }

  /**
   * Get the last offset (exclusive) of the latest snapshot file.
   */
  def latestSnapshotOffset: Option[Long] = latestSnapshotFile.map(file => offsetFromFilename(file.getName))

  /**
   * Get the last offset (exclusive) of the oldest snapshot file.
   */
  def oldestSnapshotOffset: Option[Long] = oldestSnapshotFile.map(file => offsetFromFilename(file.getName))

  private def isProducerRetained(producerIdEntry: ProducerIdEntry, logStartOffset: Long): Boolean = {
    producerIdEntry.lastOffset >= logStartOffset
  }

  /**
   * When we remove the head of the log due to retention, we need to clean up the id map. This method takes
   * the new start offset and removes all producerIds which have a smaller last written offset. Additionally,
   * we remove snapshots older than the new log start offset.
   *
   * Note that snapshots from offsets greater than the log start offset may have producers included which
   * should no longer be retained: these producers will be removed if and when we need to load state from
   * the snapshot.
   */
  def truncateHead(logStartOffset: Long) {
    val evictedProducerEntries = producers.filter { case (_, producerIdEntry) =>
      !isProducerRetained(producerIdEntry, logStartOffset)
    }
    val evictedProducerIds = evictedProducerEntries.keySet

    producers --= evictedProducerIds
    removeEvictedOngoingTransactions(evictedProducerIds)
    removeUnreplicatedTransactions(logStartOffset)

    if (lastMapOffset < logStartOffset)
      lastMapOffset = logStartOffset

    deleteSnapshotsBefore(logStartOffset)
    lastSnapOffset = latestSnapshotOffset.getOrElse(logStartOffset)
  }

  private def removeEvictedOngoingTransactions(expiredProducerIds: collection.Set[Long]): Unit = {
    val iterator = ongoingTxns.entrySet.iterator
    while (iterator.hasNext) {
      val txnEntry = iterator.next()
      if (expiredProducerIds.contains(txnEntry.getValue.producerId))
        iterator.remove()
    }
  }

  private def removeUnreplicatedTransactions(offset: Long): Unit = {
    val iterator = unreplicatedTxns.entrySet.iterator
    while (iterator.hasNext) {
      val txnEntry = iterator.next()
      val lastOffset = txnEntry.getValue.lastOffset
      if (lastOffset.exists(_ < offset))
        iterator.remove()
    }
  }

  /**
   * Truncate the producer id mapping and remove all snapshots. This resets the state of the mapping.
   */
  def truncate() {
    producers.clear()
    ongoingTxns.clear()
    unreplicatedTxns.clear()
    deleteSnapshotFiles()
    lastSnapOffset = 0L
    lastMapOffset = 0L
  }

  /**
   * Complete the transaction and return the last stable offset.
   */
  def completeTxn(completedTxn: CompletedTxn): Long = {
    val txnMetadata = ongoingTxns.remove(completedTxn.firstOffset)
    if (txnMetadata == null)
      throw new IllegalArgumentException("Attempted to complete a transaction which was not started")

    txnMetadata.lastOffset = Some(completedTxn.lastOffset)
    unreplicatedTxns.put(completedTxn.firstOffset, txnMetadata)

    val lastStableOffset = firstUndecidedOffset.getOrElse(completedTxn.lastOffset + 1)
    lastStableOffset
  }

  @threadsafe
  def deleteSnapshotsBefore(offset: Long): Unit = {
    deleteSnapshotFiles(_ < offset)
  }

  private def listSnapshotFiles: List[File] = {
    if (logDir.exists && logDir.isDirectory)
      logDir.listFiles.filter(f => f.isFile && isSnapshotFile(f.getName)).toList
    else
      List.empty[File]
  }

  private def oldestSnapshotFile: Option[File] = {
    val files = listSnapshotFiles
    if (files.nonEmpty)
      Some(files.minBy(file => offsetFromFilename(file.getName)))
    else
      None
  }

  private def latestSnapshotFile: Option[File] = {
    val files = listSnapshotFiles
    if (files.nonEmpty)
      Some(files.maxBy(file => offsetFromFilename(file.getName)))
    else
      None
  }

  private def deleteSnapshotFiles(predicate: Long => Boolean = _ => true) {
    listSnapshotFiles.filter(file => predicate(offsetFromFilename(file.getName)))
      .foreach(file => Files.deleteIfExists(file.toPath))
  }

}