core/src/main/scala/kafka/log/Log.scala - kafka - Git at Google

 /**
  * 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.{File, IOException}
 import java.lang.{Long => JLong}
 import java.nio.file.{Files, NoSuchFileException}
 import java.text.NumberFormat
 import java.util.Map.{Entry => JEntry}
 import java.util.Optional
 import java.util.concurrent.atomic._
 import java.util.concurrent.{ConcurrentNavigableMap, ConcurrentSkipListMap, TimeUnit}
 import java.util.regex.Pattern

 import com.yammer.metrics.core.Gauge
 import kafka.api.{ApiVersion, KAFKA_0_10_0_IV0}
 import kafka.common.{LogSegmentOffsetOverflowException, LongRef, OffsetsOutOfOrderException, UnexpectedAppendOffsetException}
 import kafka.message.{BrokerCompressionCodec, CompressionCodec, NoCompressionCodec}
 import kafka.metrics.KafkaMetricsGroup
 import kafka.server.checkpoints.LeaderEpochCheckpointFile
 import kafka.server.epoch.LeaderEpochFileCache
 import kafka.server.{BrokerTopicStats, FetchDataInfo, LogDirFailureChannel, LogOffsetMetadata, OffsetAndEpoch}
 import kafka.utils._
 import org.apache.kafka.common.errors._
 import org.apache.kafka.common.record.FileRecords.TimestampAndOffset
 import org.apache.kafka.common.record._
 import org.apache.kafka.common.requests.FetchResponse.AbortedTransaction
 import org.apache.kafka.common.requests.{EpochEndOffset, ListOffsetRequest}
 import org.apache.kafka.common.utils.{Time, Utils}
 import org.apache.kafka.common.{KafkaException, TopicPartition}

 import scala.collection.JavaConverters._
 import scala.collection.mutable.{ArrayBuffer, ListBuffer}
 import scala.collection.{Seq, Set, mutable}

 object LogAppendInfo {
   val UnknownLogAppendInfo = LogAppendInfo(None, -1, RecordBatch.NO_TIMESTAMP, -1L, RecordBatch.NO_TIMESTAMP, -1L,
     RecordConversionStats.EMPTY, NoCompressionCodec, NoCompressionCodec, -1, -1, offsetsMonotonic = false, -1L)

   def unknownLogAppendInfoWithLogStartOffset(logStartOffset: Long): LogAppendInfo =
     LogAppendInfo(None, -1, RecordBatch.NO_TIMESTAMP, -1L, RecordBatch.NO_TIMESTAMP, logStartOffset,
       RecordConversionStats.EMPTY, NoCompressionCodec, NoCompressionCodec, -1, -1, offsetsMonotonic = false, -1L)
 }

 /**
  * Struct to hold various quantities we compute about each message set before appending to the log
  *
  * @param firstOffset The first offset in the message set unless the message format is less than V2 and we are appending
  *                    to the follower.
  * @param lastOffset The last offset in the message set
  * @param maxTimestamp The maximum timestamp of the message set.
  * @param offsetOfMaxTimestamp The offset of the message with the maximum timestamp.
  * @param logAppendTime The log append time (if used) of the message set, otherwise Message.NoTimestamp
  * @param logStartOffset The start offset of the log at the time of this append.
  * @param recordConversionStats Statistics collected during record processing, `null` if `assignOffsets` is `false`
  * @param sourceCodec The source codec used in the message set (send by the producer)
  * @param targetCodec The target codec of the message set(after applying the broker compression configuration if any)
  * @param shallowCount The number of shallow messages
  * @param validBytes The number of valid bytes
  * @param offsetsMonotonic Are the offsets in this message set monotonically increasing
  * @param lastOffsetOfFirstBatch The last offset of the first batch
  */
 case class LogAppendInfo(var firstOffset: Option[Long],
                          var lastOffset: Long,
                          var maxTimestamp: Long,
                          var offsetOfMaxTimestamp: Long,
                          var logAppendTime: Long,
                          var logStartOffset: Long,
                          var recordConversionStats: RecordConversionStats,
                          sourceCodec: CompressionCodec,
                          targetCodec: CompressionCodec,
                          shallowCount: Int,
                          validBytes: Int,
                          offsetsMonotonic: Boolean,
                          lastOffsetOfFirstBatch: Long) {
   /**
    * Get the first offset if it exists, else get the last offset of the first batch
    * For magic versions 2 and newer, this method will return first offset. For magic versions
    * older than 2, we use the last offset of the first batch as an approximation of the first
    * offset to avoid decompressing the data.
    */
   def firstOrLastOffsetOfFirstBatch: Long = firstOffset.getOrElse(lastOffsetOfFirstBatch)

   /**
    * Get the (maximum) number of messages described by LogAppendInfo
    * @return Maximum possible number of messages described by LogAppendInfo
    */
   def numMessages: Long = {
     firstOffset match {
       case Some(firstOffsetVal) if (firstOffsetVal >= 0 && lastOffset >= 0) => (lastOffset - firstOffsetVal + 1)
       case _ => 0
     }
   }
 }

 /**
  * Container class which represents a snapshot of the significant offsets for a partition. This allows fetching
  * of these offsets atomically without the possibility of a leader change affecting their consistency relative
  * to each other. See [[kafka.cluster.Partition.fetchOffsetSnapshot()]].
  */
 case class LogOffsetSnapshot(logStartOffset: Long,
                              logEndOffset: LogOffsetMetadata,
                              highWatermark: LogOffsetMetadata,
                              lastStableOffset: LogOffsetMetadata)

 /**
  * Another container which is used for lower level reads using  [[kafka.cluster.Partition.readRecords()]].
  */
 case class LogReadInfo(fetchedData: FetchDataInfo,
                        highWatermark: Long,
                        logStartOffset: Long,
                        logEndOffset: Long,
                        lastStableOffset: Long)

 /**
  * A class used to hold useful metadata about a completed transaction. This is used to build
  * the transaction index after appending to the log.
  *
  * @param producerId The ID of the producer
  * @param firstOffset The first offset (inclusive) of the transaction
  * @param lastOffset The last offset (inclusive) of the transaction. This is always the offset of the
  *                   COMMIT/ABORT control record which indicates the transaction's completion.
  * @param isAborted Whether or not the transaction was aborted
  */
 case class CompletedTxn(producerId: Long, firstOffset: Long, lastOffset: Long, isAborted: Boolean) {
   override def toString: String = {
     "CompletedTxn(" +
       s"producerId=$producerId, " +
       s"firstOffset=$firstOffset, " +
       s"lastOffset=$lastOffset, " +
       s"isAborted=$isAborted)"
   }
 }

 /**
  * A class used to hold params required to decide to rotate a log segment or not.
  */
 case class RollParams(maxSegmentMs: Long,
                       maxSegmentBytes: Int,
                       maxTimestampInMessages: Long,
                       maxOffsetInMessages: Long,
                       messagesSize: Int,
                       now: Long)

 object RollParams {
   def apply(config: LogConfig, appendInfo: LogAppendInfo, messagesSize: Int, now: Long): RollParams = {
    new RollParams(config.maxSegmentMs,
      config.segmentSize,
      appendInfo.maxTimestamp,
      appendInfo.lastOffset,
      messagesSize, now)
   }
 }

 /**
  * An append-only log for storing messages.
  *
  * The log is a sequence of LogSegments, each with a base offset denoting the first message in the segment.
  *
  * New log segments are created according to a configurable policy that controls the size in bytes or time interval
  * for a given segment.
  *
  * @param dir The directory in which log segments are created.
  * @param config The log configuration settings
  * @param logStartOffset The earliest offset allowed to be exposed to kafka client.
  *                       The logStartOffset can be updated by :
  *                       - user's DeleteRecordsRequest
  *                       - broker's log retention
  *                       - broker's log truncation
  *                       The logStartOffset is used to decide the following:
  *                       - Log deletion. LogSegment whose nextOffset <= log's logStartOffset can be deleted.
  *                         It may trigger log rolling if the active segment is deleted.
  *                       - Earliest offset of the log in response to ListOffsetRequest. To avoid OffsetOutOfRange exception after user seeks to earliest offset,
  *                         we make sure that logStartOffset <= log's highWatermark
  *                       Other activities such as log cleaning are not affected by logStartOffset.
  * @param recoveryPoint The offset at which to begin recovery--i.e. the first offset which has not been flushed to disk
  * @param scheduler The thread pool scheduler used for background actions
  * @param brokerTopicStats Container for Broker Topic Yammer Metrics
  * @param time The time instance used for checking the clock
  * @param maxProducerIdExpirationMs The maximum amount of time to wait before a producer id is considered expired
  * @param producerIdExpirationCheckIntervalMs How often to check for producer ids which need to be expired
  */
 @threadsafe
 class Log(@volatile var dir: File,
           @volatile var config: LogConfig,
           @volatile var logStartOffset: Long,
           @volatile var recoveryPoint: Long,
           scheduler: Scheduler,
           brokerTopicStats: BrokerTopicStats,
           val time: Time,
           val maxProducerIdExpirationMs: Int,
           val producerIdExpirationCheckIntervalMs: Int,
           val topicPartition: TopicPartition,
           val producerStateManager: ProducerStateManager,
           logDirFailureChannel: LogDirFailureChannel) extends Logging with KafkaMetricsGroup {

   import kafka.log.Log._

   this.logIdent = s"[Log partition=$topicPartition, dir=${dir.getParent}] "

   /* A lock that guards all modifications to the log */
   private val lock = new Object
   // The memory mapped buffer for index files of this log will be closed with either delete() or closeHandlers()
   // After memory mapped buffer is closed, no disk IO operation should be performed for this log
   @volatile private var isMemoryMappedBufferClosed = false

   /* last time it was flushed */
   private val lastFlushedTime = new AtomicLong(time.milliseconds)

   def initFileSize: Int = {
     if (config.preallocate)
       config.segmentSize
     else
       0
   }

   def updateConfig(updatedKeys: Set[String], newConfig: LogConfig): Unit = {
     val oldConfig = this.config
     this.config = newConfig
     if (updatedKeys.contains(LogConfig.MessageFormatVersionProp)) {
       val oldRecordVersion = oldConfig.messageFormatVersion.recordVersion
       val newRecordVersion = newConfig.messageFormatVersion.recordVersion
       if (newRecordVersion.precedes(oldRecordVersion))
         warn(s"Record format version has been downgraded from $oldRecordVersion to $newRecordVersion.")
       initializeLeaderEpochCache()
     }
   }

   private def checkIfMemoryMappedBufferClosed(): Unit = {
     if (isMemoryMappedBufferClosed)
       throw new KafkaStorageException(s"The memory mapped buffer for log of $topicPartition is already closed")
   }

   @volatile private var nextOffsetMetadata: LogOffsetMetadata = _

   /* The earliest offset which is part of an incomplete transaction. This is used to compute the
    * last stable offset (LSO) in ReplicaManager. Note that it is possible that the "true" first unstable offset
    * gets removed from the log (through record or segment deletion). In this case, the first unstable offset
    * will point to the log start offset, which may actually be either part of a completed transaction or not
    * part of a transaction at all. However, since we only use the LSO for the purpose of restricting the
    * read_committed consumer to fetching decided data (i.e. committed, aborted, or non-transactional), this
    * temporary abuse seems justifiable and saves us from scanning the log after deletion to find the first offsets
    * of each ongoing transaction in order to compute a new first unstable offset. It is possible, however,
    * that this could result in disagreement between replicas depending on when they began replicating the log.
    * In the worst case, the LSO could be seen by a consumer to go backwards.
    */
   @volatile var firstUnstableOffset: Option[LogOffsetMetadata] = None

   /* Keep track of the current high watermark in order to ensure that segments containing offsets at or above it are
    * not eligible for deletion. This means that the active segment is only eligible for deletion if the high watermark
    * equals the log end offset (which may never happen for a partition under consistent load). This is needed to
    * prevent the log start offset (which is exposed in fetch responses) from getting ahead of the high watermark.
    */
   @volatile private var replicaHighWatermark: Option[Long] = None

   /* the actual segments of the log */
   private val segments: ConcurrentNavigableMap[java.lang.Long, LogSegment] = new ConcurrentSkipListMap[java.lang.Long, LogSegment]

   // Visible for testing
   @volatile var leaderEpochCache: Option[LeaderEpochFileCache] = None

   locally {
     val startMs = time.milliseconds

     // create the log directory if it doesn't exist
     Files.createDirectories(dir.toPath)

     initializeLeaderEpochCache()

     val nextOffset = loadSegments()

     /* Calculate the offset of the next message */
     nextOffsetMetadata = new LogOffsetMetadata(nextOffset, activeSegment.baseOffset, activeSegment.size)

     leaderEpochCache.foreach(_.truncateFromEnd(nextOffsetMetadata.messageOffset))

     logStartOffset = math.max(logStartOffset, segments.firstEntry.getValue.baseOffset)

     // The earliest leader epoch may not be flushed during a hard failure. Recover it here.
     leaderEpochCache.foreach(_.truncateFromStart(logStartOffset))

     // Any segment loading or recovery code must not use producerStateManager, so that we can build the full state here
     // from scratch.
     if (!producerStateManager.isEmpty)
       throw new IllegalStateException("Producer state must be empty during log initialization")
     loadProducerState(logEndOffset, reloadFromCleanShutdown = hasCleanShutdownFile)

     info(s"Completed load of log with ${segments.size} segments, log start offset $logStartOffset and " +
       s"log end offset $logEndOffset in ${time.milliseconds() - startMs} ms")
   }

   private val tags = {
     val maybeFutureTag = if (isFuture) Map("is-future" -> "true") else Map.empty[String, String]
     Map("topic" -> topicPartition.topic, "partition" -> topicPartition.partition.toString) ++ maybeFutureTag
   }

   newGauge("NumLogSegments",
     new Gauge[Int] {
       def value = numberOfSegments
     },
     tags)

   newGauge("LogStartOffset",
     new Gauge[Long] {
       def value = logStartOffset
     },
     tags)

   newGauge("LogEndOffset",
     new Gauge[Long] {
       def value = logEndOffset
     },
     tags)

   newGauge("Size",
     new Gauge[Long] {
       def value = size
     },
     tags)

   scheduler.schedule(name = "PeriodicProducerExpirationCheck", fun = () => {
     lock synchronized {
       producerStateManager.removeExpiredProducers(time.milliseconds)
     }
   }, period = producerIdExpirationCheckIntervalMs, delay = producerIdExpirationCheckIntervalMs, unit = TimeUnit.MILLISECONDS)

   /** The name of this log */
   def name  = dir.getName()

   def recordVersion: RecordVersion = config.messageFormatVersion.recordVersion

   private def initializeLeaderEpochCache(): Unit = lock synchronized {
     val leaderEpochFile = LeaderEpochCheckpointFile.newFile(dir)

     def newLeaderEpochFileCache(): LeaderEpochFileCache = {
       val checkpointFile = new LeaderEpochCheckpointFile(leaderEpochFile, logDirFailureChannel)
       new LeaderEpochFileCache(topicPartition, logEndOffset _, checkpointFile)
     }

     if (recordVersion.precedes(RecordVersion.V2)) {
       val currentCache = if (leaderEpochFile.exists())
         Some(newLeaderEpochFileCache())
       else
         None

       if (currentCache.exists(_.nonEmpty))
         warn(s"Deleting non-empty leader epoch cache due to incompatible message format $recordVersion")

       Files.deleteIfExists(leaderEpochFile.toPath)
       leaderEpochCache = None
     } else {
       leaderEpochCache = Some(newLeaderEpochFileCache())
     }
   }

   /**
    * Removes any temporary files found in log directory, and creates a list of all .swap files which could be swapped
    * in place of existing segment(s). For log splitting, we know that any .swap file whose base offset is higher than
    * the smallest offset .clean file could be part of an incomplete split operation. Such .swap files are also deleted
    * by this method.
    * @return Set of .swap files that are valid to be swapped in as segment files
    */
   private def removeTempFilesAndCollectSwapFiles(): Set[File] = {

     def deleteIndicesIfExist(baseFile: File, suffix: String = ""): Unit = {
       info(s"Deleting index files with suffix $suffix for baseFile $baseFile")
       val offset = offsetFromFile(baseFile)
       Files.deleteIfExists(Log.offsetIndexFile(dir, offset, suffix).toPath)
       Files.deleteIfExists(Log.timeIndexFile(dir, offset, suffix).toPath)
       Files.deleteIfExists(Log.transactionIndexFile(dir, offset, suffix).toPath)
     }

     var swapFiles = Set[File]()
     var cleanFiles = Set[File]()
     var minCleanedFileOffset = Long.MaxValue

     for (file <- dir.listFiles if file.isFile) {
       if (!file.canRead)
         throw new IOException(s"Could not read file $file")
       val filename = file.getName
       if (filename.endsWith(DeletedFileSuffix)) {
         debug(s"Deleting stray temporary file ${file.getAbsolutePath}")
         Files.deleteIfExists(file.toPath)
       } else if (filename.endsWith(CleanedFileSuffix)) {
         minCleanedFileOffset = Math.min(offsetFromFileName(filename), minCleanedFileOffset)
         cleanFiles += file
       } else if (filename.endsWith(SwapFileSuffix)) {
         // we crashed in the middle of a swap operation, to recover:
         // if a log, delete the index files, complete the swap operation later
         // if an index just delete the index files, they will be rebuilt
         val baseFile = new File(CoreUtils.replaceSuffix(file.getPath, SwapFileSuffix, ""))
         info(s"Found file ${file.getAbsolutePath} from interrupted swap operation.")
         if (isIndexFile(baseFile)) {
           deleteIndicesIfExist(baseFile)
         } else if (isLogFile(baseFile)) {
           deleteIndicesIfExist(baseFile)
           swapFiles += file
         }
       }
     }

     // KAFKA-6264: Delete all .swap files whose base offset is greater than the minimum .cleaned segment offset. Such .swap
     // files could be part of an incomplete split operation that could not complete. See Log#splitOverflowedSegment
     // for more details about the split operation.
     val (invalidSwapFiles, validSwapFiles) = swapFiles.partition(file => offsetFromFile(file) >= minCleanedFileOffset)
     invalidSwapFiles.foreach { file =>
       debug(s"Deleting invalid swap file ${file.getAbsoluteFile} minCleanedFileOffset: $minCleanedFileOffset")
       val baseFile = new File(CoreUtils.replaceSuffix(file.getPath, SwapFileSuffix, ""))
       deleteIndicesIfExist(baseFile, SwapFileSuffix)
       Files.deleteIfExists(file.toPath)
     }

     // Now that we have deleted all .swap files that constitute an incomplete split operation, let's delete all .clean files
     cleanFiles.foreach { file =>
       debug(s"Deleting stray .clean file ${file.getAbsolutePath}")
       Files.deleteIfExists(file.toPath)
     }

     validSwapFiles
   }

   /**
    * This method does not need to convert IOException to KafkaStorageException because it is only called before all logs are loaded
    * It is possible that we encounter a segment with index offset overflow in which case the LogSegmentOffsetOverflowException
    * will be thrown. Note that any segments that were opened before we encountered the exception will remain open and the
    * caller is responsible for closing them appropriately, if needed.
    * @throws LogSegmentOffsetOverflowException if the log directory contains a segment with messages that overflow the index offset
    */
   private def loadSegmentFiles(): Unit = {
     // load segments in ascending order because transactional data from one segment may depend on the
     // segments that come before it
     for (file <- dir.listFiles.sortBy(_.getName) if file.isFile) {
       if (isIndexFile(file)) {
         // if it is an index file, make sure it has a corresponding .log file
         val offset = offsetFromFile(file)
         val logFile = Log.logFile(dir, offset)
         if (!logFile.exists) {
           warn(s"Found an orphaned index file ${file.getAbsolutePath}, with no corresponding log file.")
           Files.deleteIfExists(file.toPath)
         }
       } else if (isLogFile(file)) {
         // if it's a log file, load the corresponding log segment
         val baseOffset = offsetFromFile(file)
         val timeIndexFileNewlyCreated = !Log.timeIndexFile(dir, baseOffset).exists()
         val segment = LogSegment.open(dir = dir,
           baseOffset = baseOffset,
           config,
           time = time,
           fileAlreadyExists = true)

         try segment.sanityCheck(timeIndexFileNewlyCreated)
         catch {
           case _: NoSuchFileException =>
             error(s"Could not find offset index file corresponding to log file ${segment.log.file.getAbsolutePath}, " +
               "recovering segment and rebuilding index files...")
             recoverSegment(segment)
           case e: CorruptIndexException =>
             warn(s"Found a corrupted index file corresponding to log file ${segment.log.file.getAbsolutePath} due " +
               s"to ${e.getMessage}}, recovering segment and rebuilding index files...")
             recoverSegment(segment)
         }
         addSegment(segment)
       }
     }
   }

   /**
    * Recover the given segment.
    * @param segment Segment to recover
    * @param leaderEpochCache Optional cache for updating the leader epoch during recovery
    * @return The number of bytes truncated from the segment
    * @throws LogSegmentOffsetOverflowException if the segment contains messages that cause index offset overflow
    */
   private def recoverSegment(segment: LogSegment,
                              leaderEpochCache: Option[LeaderEpochFileCache] = None): Int = lock synchronized {
     val producerStateManager = new ProducerStateManager(topicPartition, dir, maxProducerIdExpirationMs)
     rebuildProducerState(segment.baseOffset, reloadFromCleanShutdown = false, producerStateManager)
     val bytesTruncated = segment.recover(producerStateManager, leaderEpochCache)
     // once we have recovered the segment's data, take a snapshot to ensure that we won't
     // need to reload the same segment again while recovering another segment.
     producerStateManager.takeSnapshot()
     bytesTruncated
   }

   /**
    * This method does not need to convert IOException to KafkaStorageException because it is only called before all logs
    * are loaded.
    * @throws LogSegmentOffsetOverflowException if the swap file contains messages that cause the log segment offset to
    *                                           overflow. Note that this is currently a fatal exception as we do not have
    *                                           a way to deal with it. The exception is propagated all the way up to
    *                                           KafkaServer#startup which will cause the broker to shut down if we are in
    *                                           this situation. This is expected to be an extremely rare scenario in practice,
    *                                           and manual intervention might be required to get out of it.
    */
   private def completeSwapOperations(swapFiles: Set[File]): Unit = {
     for (swapFile <- swapFiles) {
       val logFile = new File(CoreUtils.replaceSuffix(swapFile.getPath, SwapFileSuffix, ""))
       val baseOffset = offsetFromFile(logFile)
       val swapSegment = LogSegment.open(swapFile.getParentFile,
         baseOffset = baseOffset,
         config,
         time = time,
         fileSuffix = SwapFileSuffix)
       info(s"Found log file ${swapFile.getPath} from interrupted swap operation, repairing.")
       recoverSegment(swapSegment)

       // We create swap files for two cases:
       // (1) Log cleaning where multiple segments are merged into one, and
       // (2) Log splitting where one segment is split into multiple.
       //
       // Both of these mean that the resultant swap segments be composed of the original set, i.e. the swap segment
       // must fall within the range of existing segment(s). If we cannot find such a segment, it means the deletion
       // of that segment was successful. In such an event, we should simply rename the .swap to .log without having to
       // do a replace with an existing segment.
       val oldSegments = logSegments(swapSegment.baseOffset, swapSegment.readNextOffset).filter { segment =>
         segment.readNextOffset > swapSegment.baseOffset
       }
       replaceSegments(Seq(swapSegment), oldSegments.toSeq, isRecoveredSwapFile = true)
     }
   }

   /**
    * Load the log segments from the log files on disk and return the next offset.
    * This method does not need to convert IOException to KafkaStorageException because it is only called before all logs
    * are loaded.
    * @throws LogSegmentOffsetOverflowException if we encounter a .swap file with messages that overflow index offset; or when
    *                                           we find an unexpected number of .log files with overflow
    */
   private def loadSegments(): Long = {
     // first do a pass through the files in the log directory and remove any temporary files
     // and find any interrupted swap operations
     val swapFiles = removeTempFilesAndCollectSwapFiles()

     // Now do a second pass and load all the log and index files.
     // We might encounter legacy log segments with offset overflow (KAFKA-6264). We need to split such segments. When
     // this happens, restart loading segment files from scratch.
     retryOnOffsetOverflow {
       // In case we encounter a segment with offset overflow, the retry logic will split it after which we need to retry
       // loading of segments. In that case, we also need to close all segments that could have been left open in previous
       // call to loadSegmentFiles().
       logSegments.foreach(_.close())
       segments.clear()
       loadSegmentFiles()
     }

     // Finally, complete any interrupted swap operations. To be crash-safe,
     // log files that are replaced by the swap segment should be renamed to .deleted
     // before the swap file is restored as the new segment file.
     completeSwapOperations(swapFiles)

     if (!dir.getAbsolutePath.endsWith(Log.DeleteDirSuffix)) {
       val nextOffset = retryOnOffsetOverflow {
         recoverLog()
       }

       // reset the index size of the currently active log segment to allow more entries
       activeSegment.resizeIndexes(config.maxIndexSize)
       nextOffset
     } else {
        if (logSegments.isEmpty) {
           addSegment(LogSegment.open(dir = dir,
             baseOffset = 0,
             config,
             time = time,
             fileAlreadyExists = false,
             initFileSize = this.initFileSize,
             preallocate = false))
        }
       0
     }
   }

   private def updateLogEndOffset(messageOffset: Long) {
     nextOffsetMetadata = new LogOffsetMetadata(messageOffset, activeSegment.baseOffset, activeSegment.size)
   }

   /**
    * Recover the log segments and return the next offset after recovery.
    * This method does not need to convert IOException to KafkaStorageException because it is only called before all
    * logs are loaded.
    * @throws LogSegmentOffsetOverflowException if we encountered a legacy segment with offset overflow
    */
   private def recoverLog(): Long = {
     // if we have the clean shutdown marker, skip recovery
     if (!hasCleanShutdownFile) {
       // okay we need to actually recover this log
       val unflushed = logSegments(this.recoveryPoint, Long.MaxValue).iterator
       while (unflushed.hasNext) {
         val segment = unflushed.next
         info(s"Recovering unflushed segment ${segment.baseOffset}")
         val truncatedBytes =
           try {
             recoverSegment(segment, leaderEpochCache)
           } catch {
             case _: InvalidOffsetException =>
               val startOffset = segment.baseOffset
               warn("Found invalid offset during recovery. Deleting the corrupt segment and " +
                 s"creating an empty one with starting offset $startOffset")
               segment.truncateTo(startOffset)
           }
         if (truncatedBytes > 0) {
           // we had an invalid message, delete all remaining log
           warn(s"Corruption found in segment ${segment.baseOffset}, truncating to offset ${segment.readNextOffset}")
           unflushed.foreach(deleteSegment)
         }
       }
     }

     if (logSegments.nonEmpty) {
       val logEndOffset = activeSegment.readNextOffset
       if (logEndOffset < logStartOffset) {
         warn(s"Deleting all segments because logEndOffset ($logEndOffset) is smaller than logStartOffset ($logStartOffset). " +
           "This could happen if segment files were deleted from the file system.")
         logSegments.foreach(deleteSegment)
       }
     }

     if (logSegments.isEmpty) {
       // no existing segments, create a new mutable segment beginning at logStartOffset
       addSegment(LogSegment.open(dir = dir,
         baseOffset = logStartOffset,
         config,
         time = time,
         fileAlreadyExists = false,
         initFileSize = this.initFileSize,
         preallocate = config.preallocate))
     }

     recoveryPoint = activeSegment.readNextOffset
     recoveryPoint
   }

   // Rebuild producer state until lastOffset. This method may be called from the recovery code path, and thus must be
   // free of all side-effects, i.e. it must not update any log-specific state.
   private def rebuildProducerState(lastOffset: Long,
                                    reloadFromCleanShutdown: Boolean,
                                    producerStateManager: ProducerStateManager): Unit = lock synchronized {
     checkIfMemoryMappedBufferClosed()
     val messageFormatVersion = config.messageFormatVersion.recordVersion.value
     val segments = logSegments
     val offsetsToSnapshot =
       if (segments.nonEmpty) {
         val nextLatestSegmentBaseOffset = lowerSegment(segments.last.baseOffset).map(_.baseOffset)
         Seq(nextLatestSegmentBaseOffset, Some(segments.last.baseOffset), Some(lastOffset))
       } else {
         Seq(Some(lastOffset))
       }
     info(s"Loading producer state till offset $lastOffset with message format version $messageFormatVersion")

     // We want to avoid unnecessary scanning of the log to build the producer state when the broker is being
     // upgraded. The basic idea is to use the absence of producer snapshot files to detect the upgrade case,
     // but we have to be careful not to assume too much in the presence of broker failures. The two most common
     // upgrade cases in which we expect to find no snapshots are the following:
     //
     // 1. The broker has been upgraded, but the topic is still on the old message format.
     // 2. The broker has been upgraded, the topic is on the new message format, and we had a clean shutdown.
     //
     // If we hit either of these cases, we skip producer state loading and write a new snapshot at the log end
     // offset (see below). The next time the log is reloaded, we will load producer state using this snapshot
     // (or later snapshots). Otherwise, if there is no snapshot file, then we have to rebuild producer state
     // from the first segment.
     if (messageFormatVersion < RecordBatch.MAGIC_VALUE_V2 ||
         (producerStateManager.latestSnapshotOffset.isEmpty && reloadFromCleanShutdown)) {
       // To avoid an expensive scan through all of the segments, we take empty snapshots from the start of the
       // last two segments and the last offset. This should avoid the full scan in the case that the log needs
       // truncation.
       offsetsToSnapshot.flatten.foreach { offset =>
         producerStateManager.updateMapEndOffset(offset)
         producerStateManager.takeSnapshot()
       }
     } else {
       val isEmptyBeforeTruncation = producerStateManager.isEmpty && producerStateManager.mapEndOffset >= lastOffset
       producerStateManager.truncateAndReload(logStartOffset, lastOffset, time.milliseconds())

       // Only do the potentially expensive reloading if the last snapshot offset is lower than the log end
       // offset (which would be the case on first startup) and there were active producers prior to truncation
       // (which could be the case if truncating after initial loading). If there weren't, then truncating
       // shouldn't change that fact (although it could cause a producerId to expire earlier than expected),
       // and we can skip the loading. This is an optimization for users which are not yet using
       // idempotent/transactional features yet.
       if (lastOffset > producerStateManager.mapEndOffset && !isEmptyBeforeTruncation) {
         logSegments(producerStateManager.mapEndOffset, lastOffset).foreach { segment =>
           val startOffset = Utils.max(segment.baseOffset, producerStateManager.mapEndOffset, logStartOffset)
           producerStateManager.updateMapEndOffset(startOffset)

           if (offsetsToSnapshot.contains(Some(segment.baseOffset)))
             producerStateManager.takeSnapshot()

           val fetchDataInfo = segment.read(startOffset, Some(lastOffset), Int.MaxValue)
           if (fetchDataInfo != null)
             loadProducersFromLog(producerStateManager, fetchDataInfo.records)
         }
       }
       producerStateManager.updateMapEndOffset(lastOffset)
       producerStateManager.takeSnapshot()
     }
   }

   private def loadProducerState(lastOffset: Long, reloadFromCleanShutdown: Boolean): Unit = lock synchronized {
     rebuildProducerState(lastOffset, reloadFromCleanShutdown, producerStateManager)
     updateFirstUnstableOffset()
   }

   private def loadProducersFromLog(producerStateManager: ProducerStateManager, records: Records): Unit = {
     val loadedProducers = mutable.Map.empty[Long, ProducerAppendInfo]
     val completedTxns = ListBuffer.empty[CompletedTxn]
     records.batches.asScala.foreach { batch =>
       if (batch.hasProducerId) {
         val maybeCompletedTxn = updateProducers(batch, loadedProducers, isFromClient = false)
         maybeCompletedTxn.foreach(completedTxns += _)
       }
     }
     loadedProducers.values.foreach(producerStateManager.update)
     completedTxns.foreach(producerStateManager.completeTxn)
   }

   private[log] def activeProducersWithLastSequence: Map[Long, Int] = lock synchronized {
     producerStateManager.activeProducers.map { case (producerId, producerIdEntry) =>
       (producerId, producerIdEntry.lastSeq)
     }
   }

   private[log] def lastRecordsOfActiveProducers: Map[Long, LastRecord] = lock synchronized {
     producerStateManager.activeProducers.map { case (producerId, producerIdEntry) =>
       val lastDataOffset = if (producerIdEntry.lastDataOffset >= 0 ) Some(producerIdEntry.lastDataOffset) else None
       val lastRecord = LastRecord(lastDataOffset, producerIdEntry.producerEpoch)
       producerId -> lastRecord
     }
   }

   /**
    * Check if we have the "clean shutdown" file
    */
   private def hasCleanShutdownFile: Boolean = new File(dir.getParentFile, CleanShutdownFile).exists()

   /**
    * The number of segments in the log.
    * Take care! this is an O(n) operation.
    */
   def numberOfSegments: Int = segments.size

   /**
    * Close this log.
    * The memory mapped buffer for index files of this log will be left open until the log is deleted.
    */
   def close() {
     debug("Closing log")
     lock synchronized {
       checkIfMemoryMappedBufferClosed()
       maybeHandleIOException(s"Error while renaming dir for $topicPartition in dir ${dir.getParent}") {
         // We take a snapshot at the last written offset to hopefully avoid the need to scan the log
         // after restarting and to ensure that we cannot inadvertently hit the upgrade optimization
         // (the clean shutdown file is written after the logs are all closed).
         producerStateManager.takeSnapshot()
         logSegments.foreach(_.close())
       }
     }
   }

   /**
    * Rename the directory of the log
    *
    * @throws KafkaStorageException if rename fails
    */
   def renameDir(name: String) {
     lock synchronized {
       maybeHandleIOException(s"Error while renaming dir for $topicPartition in log dir ${dir.getParent}") {
         val renamedDir = new File(dir.getParent, name)
         Utils.atomicMoveWithFallback(dir.toPath, renamedDir.toPath)
         if (renamedDir != dir) {
           dir = renamedDir
           logSegments.foreach(_.updateDir(renamedDir))
           producerStateManager.logDir = dir
           // re-initialize leader epoch cache so that LeaderEpochCheckpointFile.checkpoint can correctly reference
           // the checkpoint file in renamed log directory
           initializeLeaderEpochCache()
         }
       }
     }
   }

   /**
    * Close file handlers used by log but don't write to disk. This is called if the log directory is offline
    */
   def closeHandlers() {
     debug("Closing handlers")
     lock synchronized {
       logSegments.foreach(_.closeHandlers())
       isMemoryMappedBufferClosed = true
     }
   }

   /**
    * Append this message set to the active segment of the log, assigning offsets and Partition Leader Epochs
    *
    * @param records The records to append
    * @param isFromClient Whether or not this append is from a producer
    * @param interBrokerProtocolVersion Inter-broker message protocol version
    * @throws KafkaStorageException If the append fails due to an I/O error.
    * @return Information about the appended messages including the first and last offset.
    */
   def appendAsLeader(records: MemoryRecords, leaderEpoch: Int, isFromClient: Boolean = true,
                      interBrokerProtocolVersion: ApiVersion = ApiVersion.latestVersion): LogAppendInfo = {
     append(records, isFromClient, interBrokerProtocolVersion, assignOffsets = true, leaderEpoch)
   }

   /**
    * Append this message set to the active segment of the log without assigning offsets or Partition Leader Epochs
    *
    * @param records The records to append
    * @throws KafkaStorageException If the append fails due to an I/O error.
    * @return Information about the appended messages including the first and last offset.
    */
   def appendAsFollower(records: MemoryRecords): LogAppendInfo = {
     append(records, isFromClient = false, interBrokerProtocolVersion = ApiVersion.latestVersion, assignOffsets = false, leaderEpoch = -1)
   }

   /**
    * Append this message set to the active segment of the log, rolling over to a fresh segment if necessary.
    *
    * This method will generally be responsible for assigning offsets to the messages,
    * however if the assignOffsets=false flag is passed we will only check that the existing offsets are valid.
    *
    * @param records The log records to append
    * @param isFromClient Whether or not this append is from a producer
    * @param interBrokerProtocolVersion Inter-broker message protocol version
    * @param assignOffsets Should the log assign offsets to this message set or blindly apply what it is given
    * @param leaderEpoch The partition's leader epoch which will be applied to messages when offsets are assigned on the leader
    * @throws KafkaStorageException If the append fails due to an I/O error.
    * @throws OffsetsOutOfOrderException If out of order offsets found in 'records'
    * @throws UnexpectedAppendOffsetException If the first or last offset in append is less than next offset
    * @return Information about the appended messages including the first and last offset.
    */
   private def append(records: MemoryRecords, isFromClient: Boolean, interBrokerProtocolVersion: ApiVersion, assignOffsets: Boolean, leaderEpoch: Int): LogAppendInfo = {
     maybeHandleIOException(s"Error while appending records to $topicPartition in dir ${dir.getParent}") {
       val appendInfo = analyzeAndValidateRecords(records, isFromClient = isFromClient)

       // return if we have no valid messages or if this is a duplicate of the last appended entry
       if (appendInfo.shallowCount == 0)
         return appendInfo

       // trim any invalid bytes or partial messages before appending it to the on-disk log
       var validRecords = trimInvalidBytes(records, appendInfo)

       // they are valid, insert them in the log
       lock synchronized {
         checkIfMemoryMappedBufferClosed()
         if (assignOffsets) {
           // assign offsets to the message set
           val offset = new LongRef(nextOffsetMetadata.messageOffset)
           appendInfo.firstOffset = Some(offset.value)
           val now = time.milliseconds
           val validateAndOffsetAssignResult = try {
             LogValidator.validateMessagesAndAssignOffsets(validRecords,
               offset,
               time,
               now,
               appendInfo.sourceCodec,
               appendInfo.targetCodec,
               config.compact,
               config.messageFormatVersion.recordVersion.value,
               config.messageTimestampType,
               config.messageTimestampDifferenceMaxMs,
               leaderEpoch,
               isFromClient,
               interBrokerProtocolVersion)
           } catch {
             case e: IOException =>
               throw new KafkaException(s"Error validating messages while appending to log $name", e)
           }
           validRecords = validateAndOffsetAssignResult.validatedRecords
           appendInfo.maxTimestamp = validateAndOffsetAssignResult.maxTimestamp
           appendInfo.offsetOfMaxTimestamp = validateAndOffsetAssignResult.shallowOffsetOfMaxTimestamp
           appendInfo.lastOffset = offset.value - 1
           appendInfo.recordConversionStats = validateAndOffsetAssignResult.recordConversionStats
           if (config.messageTimestampType == TimestampType.LOG_APPEND_TIME)
             appendInfo.logAppendTime = now

           // re-validate message sizes if there's a possibility that they have changed (due to re-compression or message
           // format conversion)
           if (validateAndOffsetAssignResult.messageSizeMaybeChanged) {
             for (batch <- validRecords.batches.asScala) {
               if (batch.sizeInBytes > config.maxMessageSize) {
                 // we record the original message set size instead of the trimmed size
                 // to be consistent with pre-compression bytesRejectedRate recording
                 brokerTopicStats.topicStats(topicPartition.topic).bytesRejectedRate.mark(records.sizeInBytes)
                 brokerTopicStats.allTopicsStats.bytesRejectedRate.mark(records.sizeInBytes)
                 throw new RecordTooLargeException(s"Message batch size is ${batch.sizeInBytes} bytes in append to" +
                   s"partition $topicPartition which exceeds the maximum configured size of ${config.maxMessageSize}.")
               }
             }
           }
         } else {
           // we are taking the offsets we are given
           if (!appendInfo.offsetsMonotonic)
             throw new OffsetsOutOfOrderException(s"Out of order offsets found in append to $topicPartition: " +
                                                  records.records.asScala.map(_.offset))

           if (appendInfo.firstOrLastOffsetOfFirstBatch < nextOffsetMetadata.messageOffset) {
             // we may still be able to recover if the log is empty
             // one example: fetching from log start offset on the leader which is not batch aligned,
             // which may happen as a result of AdminClient#deleteRecords()
             val firstOffset = appendInfo.firstOffset match {
               case Some(offset) => offset
               case None => records.batches.asScala.head.baseOffset()
             }

             val firstOrLast = if (appendInfo.firstOffset.isDefined) "First offset" else "Last offset of the first batch"
             throw new UnexpectedAppendOffsetException(
               s"Unexpected offset in append to $topicPartition. $firstOrLast " +
               s"${appendInfo.firstOrLastOffsetOfFirstBatch} is less than the next offset ${nextOffsetMetadata.messageOffset}. " +
               s"First 10 offsets in append: ${records.records.asScala.take(10).map(_.offset)}, last offset in" +
               s" append: ${appendInfo.lastOffset}. Log start offset = $logStartOffset",
               firstOffset, appendInfo.lastOffset)
           }
         }

         // update the epoch cache with the epoch stamped onto the message by the leader
         validRecords.batches.asScala.foreach { batch =>
           if (batch.magic >= RecordBatch.MAGIC_VALUE_V2) {
             maybeAssignEpochStartOffset(batch.partitionLeaderEpoch, batch.baseOffset)
           } else {
             // In partial upgrade scenarios, we may get a temporary regression to the message format. In
             // order to ensure the safety of leader election, we clear the epoch cache so that we revert
             // to truncation by high watermark after the next leader election.
             leaderEpochCache.filter(_.nonEmpty).foreach { cache =>
               warn(s"Clearing leader epoch cache after unexpected append with message format v${batch.magic}")
               cache.clearAndFlush()
             }
           }
         }

         // check messages set size may be exceed config.segmentSize
         if (validRecords.sizeInBytes > config.segmentSize) {
           throw new RecordBatchTooLargeException(s"Message batch size is ${validRecords.sizeInBytes} bytes in append " +
             s"to partition $topicPartition, which exceeds the maximum configured segment size of ${config.segmentSize}.")
         }

         // now that we have valid records, offsets assigned, and timestamps updated, we need to
         // validate the idempotent/transactional state of the producers and collect some metadata
         val (updatedProducers, completedTxns, maybeDuplicate) = analyzeAndValidateProducerState(validRecords, isFromClient)
         maybeDuplicate.foreach { duplicate =>
           appendInfo.firstOffset = Some(duplicate.firstOffset)
           appendInfo.lastOffset = duplicate.lastOffset
           appendInfo.logAppendTime = duplicate.timestamp
           appendInfo.logStartOffset = logStartOffset
           return appendInfo
         }

         // maybe roll the log if this segment is full
         val segment = maybeRoll(validRecords.sizeInBytes, appendInfo)

         val logOffsetMetadata = LogOffsetMetadata(
           messageOffset = appendInfo.firstOrLastOffsetOfFirstBatch,
           segmentBaseOffset = segment.baseOffset,
           relativePositionInSegment = segment.size)

         segment.append(largestOffset = appendInfo.lastOffset,
           largestTimestamp = appendInfo.maxTimestamp,
           shallowOffsetOfMaxTimestamp = appendInfo.offsetOfMaxTimestamp,
           records = validRecords)

         // Increment the log end offset. We do this immediately after the append because a
         // write to the transaction index below may fail and we want to ensure that the offsets
         // of future appends still grow monotonically. The resulting transaction index inconsistency
         // will be cleaned up after the log directory is recovered. Note that the end offset of the
         // ProducerStateManager will not be updated and the last stable offset will not advance
         // if the append to the transaction index fails.
         updateLogEndOffset(appendInfo.lastOffset + 1)

         // update the producer state
         for ((_, producerAppendInfo) <- updatedProducers) {
           producerAppendInfo.maybeCacheTxnFirstOffsetMetadata(logOffsetMetadata)
           producerStateManager.update(producerAppendInfo)
         }

         // update the transaction index with the true last stable offset. The last offset visible
         // to consumers using READ_COMMITTED will be limited by this value and the high watermark.
         for (completedTxn <- completedTxns) {
           val lastStableOffset = producerStateManager.lastStableOffset(completedTxn)
           segment.updateTxnIndex(completedTxn, lastStableOffset)
           producerStateManager.completeTxn(completedTxn)
         }

         // always update the last producer id map offset so that the snapshot reflects the current offset
         // even if there isn't any idempotent data being written
         producerStateManager.updateMapEndOffset(appendInfo.lastOffset + 1)

         // update the first unstable offset (which is used to compute LSO)
         updateFirstUnstableOffset()

         trace(s"Appended message set with last offset: ${appendInfo.lastOffset}, " +
           s"first offset: ${appendInfo.firstOffset}, " +
           s"next offset: ${nextOffsetMetadata.messageOffset}, " +
           s"and messages: $validRecords")

         if (unflushedMessages >= config.flushInterval)
           flush()

         appendInfo
       }
     }
   }

   def maybeAssignEpochStartOffset(leaderEpoch: Int, startOffset: Long): Unit = {
     leaderEpochCache.foreach { cache =>
       cache.assign(leaderEpoch, startOffset)
     }
   }

   def latestEpoch: Option[Int] = leaderEpochCache.flatMap(_.latestEpoch)

   def endOffsetForEpoch(leaderEpoch: Int): Option[OffsetAndEpoch] = {
     leaderEpochCache.flatMap { cache =>
       val (foundEpoch, foundOffset) = cache.endOffsetFor(leaderEpoch)
       if (foundOffset == EpochEndOffset.UNDEFINED_EPOCH_OFFSET)
         None
       else
         Some(OffsetAndEpoch(foundOffset, foundEpoch))
     }
   }

   def onHighWatermarkIncremented(highWatermark: Long): Unit = {
     lock synchronized {
       replicaHighWatermark = Some(highWatermark)
       producerStateManager.onHighWatermarkUpdated(highWatermark)
       updateFirstUnstableOffset()
     }
   }

   private def updateFirstUnstableOffset(): Unit = lock synchronized {
     checkIfMemoryMappedBufferClosed()
     val updatedFirstStableOffset = producerStateManager.firstUnstableOffset match {
       case Some(logOffsetMetadata) if logOffsetMetadata.messageOffsetOnly || logOffsetMetadata.messageOffset < logStartOffset =>
         val offset = math.max(logOffsetMetadata.messageOffset, logStartOffset)
         val segment = segments.floorEntry(offset).getValue
         val position  = segment.translateOffset(offset)
         Some(LogOffsetMetadata(offset, segment.baseOffset, position.position))
       case other => other
     }

     if (updatedFirstStableOffset != this.firstUnstableOffset) {
       debug(s"First unstable offset updated to $updatedFirstStableOffset")
       this.firstUnstableOffset = updatedFirstStableOffset
     }
   }

   /**
    * Increment the log start offset if the provided offset is larger.
    */
   def maybeIncrementLogStartOffset(newLogStartOffset: Long) {
     // We don't have to write the log start offset to log-start-offset-checkpoint immediately.
     // The deleteRecordsOffset may be lost only if all in-sync replicas of this broker are shutdown
     // in an unclean manner within log.flush.start.offset.checkpoint.interval.ms. The chance of this happening is low.
     maybeHandleIOException(s"Exception while increasing log start offset for $topicPartition to $newLogStartOffset in dir ${dir.getParent}") {
       lock synchronized {
         checkIfMemoryMappedBufferClosed()
         if (newLogStartOffset > logStartOffset) {
           info(s"Incrementing log start offset to $newLogStartOffset")
           logStartOffset = newLogStartOffset
           leaderEpochCache.foreach(_.truncateFromStart(logStartOffset))
           producerStateManager.truncateHead(logStartOffset)
           updateFirstUnstableOffset()
         }
       }
     }
   }

   private def analyzeAndValidateProducerState(records: MemoryRecords, isFromClient: Boolean):
   (mutable.Map[Long, ProducerAppendInfo], List[CompletedTxn], Option[BatchMetadata]) = {
     val updatedProducers = mutable.Map.empty[Long, ProducerAppendInfo]
     val completedTxns = ListBuffer.empty[CompletedTxn]
     for (batch <- records.batches.asScala if batch.hasProducerId) {
       val maybeLastEntry = producerStateManager.lastEntry(batch.producerId)

       // if this is a client produce request, there will be up to 5 batches which could have been duplicated.
       // If we find a duplicate, we return the metadata of the appended batch to the client.
       if (isFromClient) {
         maybeLastEntry.flatMap(_.findDuplicateBatch(batch)).foreach { duplicate =>
           return (updatedProducers, completedTxns.toList, Some(duplicate))
         }
       }

       val maybeCompletedTxn = updateProducers(batch, updatedProducers, isFromClient = isFromClient)
       maybeCompletedTxn.foreach(completedTxns += _)
     }
     (updatedProducers, completedTxns.toList, None)
   }

   /**
    * Validate the following:
    * <ol>
    * <li> each message matches its CRC
    * <li> each message size is valid
    * <li> that the sequence numbers of the incoming record batches are consistent with the existing state and with each other.
    * </ol>
    *
    * Also compute the following quantities:
    * <ol>
    * <li> First offset in the message set
    * <li> Last offset in the message set
    * <li> Number of messages
    * <li> Number of valid bytes
    * <li> Whether the offsets are monotonically increasing
    * <li> Whether any compression codec is used (if many are used, then the last one is given)
    * </ol>
    */
   private def analyzeAndValidateRecords(records: MemoryRecords, isFromClient: Boolean): LogAppendInfo = {
     var shallowMessageCount = 0
     var validBytesCount = 0
     var firstOffset: Option[Long] = None
     var lastOffset = -1L
     var sourceCodec: CompressionCodec = NoCompressionCodec
     var monotonic = true
     var maxTimestamp = RecordBatch.NO_TIMESTAMP
     var offsetOfMaxTimestamp = -1L
     var readFirstMessage = false
     var lastOffsetOfFirstBatch = -1L

     for (batch <- records.batches.asScala) {
       // we only validate V2 and higher to avoid potential compatibility issues with older clients
       if (batch.magic >= RecordBatch.MAGIC_VALUE_V2 && isFromClient && batch.baseOffset != 0)
         throw new InvalidRecordException(s"The baseOffset of the record batch in the append to $topicPartition should " +
           s"be 0, but it is ${batch.baseOffset}")

       // update the first offset if on the first message. For magic versions older than 2, we use the last offset
       // to avoid the need to decompress the data (the last offset can be obtained directly from the wrapper message).
       // For magic version 2, we can get the first offset directly from the batch header.
       // When appending to the leader, we will update LogAppendInfo.baseOffset with the correct value. In the follower
       // case, validation will be more lenient.
       // Also indicate whether we have the accurate first offset or not
       if (!readFirstMessage) {
         if (batch.magic >= RecordBatch.MAGIC_VALUE_V2)
           firstOffset = Some(batch.baseOffset)
         lastOffsetOfFirstBatch = batch.lastOffset
         readFirstMessage = true
       }

       // check that offsets are monotonically increasing
       if (lastOffset >= batch.lastOffset)
         monotonic = false

       // update the last offset seen
       lastOffset = batch.lastOffset

       // Check if the message sizes are valid.
       val batchSize = batch.sizeInBytes
       if (batchSize > config.maxMessageSize) {
         brokerTopicStats.topicStats(topicPartition.topic).bytesRejectedRate.mark(records.sizeInBytes)
         brokerTopicStats.allTopicsStats.bytesRejectedRate.mark(records.sizeInBytes)
         throw new RecordTooLargeException(s"The record batch size in the append to $topicPartition is $batchSize bytes " +
           s"which exceeds the maximum configured value of ${config.maxMessageSize}.")
       }

       // check the validity of the message by checking CRC
       batch.ensureValid()

       if (batch.maxTimestamp > maxTimestamp) {
         maxTimestamp = batch.maxTimestamp
         offsetOfMaxTimestamp = lastOffset
       }

       shallowMessageCount += 1
       validBytesCount += batchSize

       val messageCodec = CompressionCodec.getCompressionCodec(batch.compressionType.id)
       if (messageCodec != NoCompressionCodec)
         sourceCodec = messageCodec
     }

     // Apply broker-side compression if any
     val targetCodec = BrokerCompressionCodec.getTargetCompressionCodec(config.compressionType, sourceCodec)
     LogAppendInfo(firstOffset, lastOffset, maxTimestamp, offsetOfMaxTimestamp, RecordBatch.NO_TIMESTAMP, logStartOffset,
       RecordConversionStats.EMPTY, sourceCodec, targetCodec, shallowMessageCount, validBytesCount, monotonic, lastOffsetOfFirstBatch)
   }

   private def updateProducers(batch: RecordBatch,
                               producers: mutable.Map[Long, ProducerAppendInfo],
                               isFromClient: Boolean): Option[CompletedTxn] = {
     val producerId = batch.producerId
     val appendInfo = producers.getOrElseUpdate(producerId, producerStateManager.prepareUpdate(producerId, isFromClient))
     appendInfo.append(batch)
   }

   /**
    * Trim any invalid bytes from the end of this message set (if there are any)
    *
    * @param records The records to trim
    * @param info The general information of the message set
    * @return A trimmed message set. This may be the same as what was passed in or it may not.
    */
   private def trimInvalidBytes(records: MemoryRecords, info: LogAppendInfo): MemoryRecords = {
     val validBytes = info.validBytes
     if (validBytes < 0)
       throw new CorruptRecordException(s"Cannot append record batch with illegal length $validBytes to " +
         s"log for $topicPartition. A possible cause is a corrupted produce request.")
     if (validBytes == records.sizeInBytes) {
       records
     } else {
       // trim invalid bytes
       val validByteBuffer = records.buffer.duplicate()
       validByteBuffer.limit(validBytes)
       MemoryRecords.readableRecords(validByteBuffer)
     }
   }

   /**
    * Read messages from the log.
    *
    * @param startOffset The offset to begin reading at
    * @param maxLength The maximum number of bytes to read
    * @param maxOffset The offset to read up to, exclusive. (i.e. this offset NOT included in the resulting message set)
    * @param minOneMessage If this is true, the first message will be returned even if it exceeds `maxLength` (if one exists)
    * @param includeAbortedTxns Whether or not to lookup aborted transactions for fetched data
    * @throws OffsetOutOfRangeException If startOffset is beyond the log end offset or before the log start offset
    * @return The fetch data information including fetch starting offset metadata and messages read.
    */
   def read(startOffset: Long,
            maxLength: Int,
            maxOffset: Option[Long],
            minOneMessage: Boolean,
            includeAbortedTxns: Boolean): FetchDataInfo = {
     maybeHandleIOException(s"Exception while reading from $topicPartition in dir ${dir.getParent}") {
       trace(s"Reading $maxLength bytes from offset $startOffset of length $size bytes")

       // Because we don't use lock for reading, the synchronization is a little bit tricky.
       // We create the local variables to avoid race conditions with updates to the log.
       val currentNextOffsetMetadata = nextOffsetMetadata
       val next = currentNextOffsetMetadata.messageOffset
       if (startOffset == next) {
         val abortedTransactions =
           if (includeAbortedTxns) Some(List.empty[AbortedTransaction])
           else None
         return FetchDataInfo(currentNextOffsetMetadata, MemoryRecords.EMPTY, firstEntryIncomplete = false,
           abortedTransactions = abortedTransactions)
       }

       var segmentEntry = segments.floorEntry(startOffset)

       // return error on attempt to read beyond the log end offset or read below log start offset
       if (startOffset > next || segmentEntry == null || startOffset < logStartOffset)
         throw new OffsetOutOfRangeException(s"Received request for offset $startOffset for partition $topicPartition, " +
           s"but we only have log segments in the range $logStartOffset to $next.")

       // Do the read on the segment with a base offset less than the target offset
       // but if that segment doesn't contain any messages with an offset greater than that
       // continue to read from successive segments until we get some messages or we reach the end of the log
       while (segmentEntry != null) {
         val segment = segmentEntry.getValue

         // If the fetch occurs on the active segment, there might be a race condition where two fetch requests occur after
         // the message is appended but before the nextOffsetMetadata is updated. In that case the second fetch may
         // cause OffsetOutOfRangeException. To solve that, we cap the reading up to exposed position instead of the log
         // end of the active segment.
         val maxPosition = {
           if (segmentEntry == segments.lastEntry) {
             val exposedPos = nextOffsetMetadata.relativePositionInSegment.toLong
             // Check the segment again in case a new segment has just rolled out.
             if (segmentEntry != segments.lastEntry)
             // New log segment has rolled out, we can read up to the file end.
               segment.size
             else
               exposedPos
           } else {
             segment.size
           }
         }
         val fetchInfo = segment.read(startOffset, maxOffset, maxLength, maxPosition, minOneMessage)
         if (fetchInfo == null) {
           segmentEntry = segments.higherEntry(segmentEntry.getKey)
         } else {
           return if (includeAbortedTxns)
             addAbortedTransactions(startOffset, segmentEntry, fetchInfo)
           else
             fetchInfo
         }
       }

       // okay we are beyond the end of the last segment with no data fetched although the start offset is in range,
       // this can happen when all messages with offset larger than start offsets have been deleted.
       // In this case, we will return the empty set with log end offset metadata
       FetchDataInfo(nextOffsetMetadata, MemoryRecords.EMPTY)
     }
   }

   private[log] def collectAbortedTransactions(startOffset: Long, upperBoundOffset: Long): List[AbortedTxn] = {
     val segmentEntry = segments.floorEntry(startOffset)
     val allAbortedTxns = ListBuffer.empty[AbortedTxn]
     def accumulator(abortedTxns: List[AbortedTxn]): Unit = allAbortedTxns ++= abortedTxns
     collectAbortedTransactions(logStartOffset, upperBoundOffset, segmentEntry, accumulator)
     allAbortedTxns.toList
   }

   private def addAbortedTransactions(startOffset: Long, segmentEntry: JEntry[JLong, LogSegment],
                                      fetchInfo: FetchDataInfo): FetchDataInfo = {
     val fetchSize = fetchInfo.records.sizeInBytes
     val startOffsetPosition = OffsetPosition(fetchInfo.fetchOffsetMetadata.messageOffset,
       fetchInfo.fetchOffsetMetadata.relativePositionInSegment)
     val upperBoundOffset = segmentEntry.getValue.fetchUpperBoundOffset(startOffsetPosition, fetchSize).getOrElse {
       val nextSegmentEntry = segments.higherEntry(segmentEntry.getKey)
       if (nextSegmentEntry != null)
         nextSegmentEntry.getValue.baseOffset
       else
         logEndOffset
     }

     val abortedTransactions = ListBuffer.empty[AbortedTransaction]
     def accumulator(abortedTxns: List[AbortedTxn]): Unit = abortedTransactions ++= abortedTxns.map(_.asAbortedTransaction)
     collectAbortedTransactions(startOffset, upperBoundOffset, segmentEntry, accumulator)

     FetchDataInfo(fetchOffsetMetadata = fetchInfo.fetchOffsetMetadata,
       records = fetchInfo.records,
       firstEntryIncomplete = fetchInfo.firstEntryIncomplete,
       abortedTransactions = Some(abortedTransactions.toList))
   }

   private def collectAbortedTransactions(startOffset: Long, upperBoundOffset: Long,
                                          startingSegmentEntry: JEntry[JLong, LogSegment],
                                          accumulator: List[AbortedTxn] => Unit): Unit = {
     var segmentEntry = startingSegmentEntry
     while (segmentEntry != null) {
       val searchResult = segmentEntry.getValue.collectAbortedTxns(startOffset, upperBoundOffset)
       accumulator(searchResult.abortedTransactions)
       if (searchResult.isComplete)
         return
       segmentEntry = segments.higherEntry(segmentEntry.getKey)
     }
   }

   /**
    * Get an offset based on the given timestamp
    * The offset returned is the offset of the first message whose timestamp is greater than or equals to the
    * given timestamp.
    *
    * If no such message is found, the log end offset is returned.
    *
    * `NOTE:` OffsetRequest V0 does not use this method, the behavior of OffsetRequest V0 remains the same as before
    * , i.e. it only gives back the timestamp based on the last modification time of the log segments.
    *
    * @param targetTimestamp The given timestamp for offset fetching.
    * @return The offset of the first message whose timestamp is greater than or equals to the given timestamp.
    *         None if no such message is found.
    */
   def fetchOffsetByTimestamp(targetTimestamp: Long): Option[TimestampAndOffset] = {
     maybeHandleIOException(s"Error while fetching offset by timestamp for $topicPartition in dir ${dir.getParent}") {
       debug(s"Searching offset for timestamp $targetTimestamp")

       if (config.messageFormatVersion < KAFKA_0_10_0_IV0 &&
         targetTimestamp != ListOffsetRequest.EARLIEST_TIMESTAMP &&
         targetTimestamp != ListOffsetRequest.LATEST_TIMESTAMP)
         throw new UnsupportedForMessageFormatException(s"Cannot search offsets based on timestamp because message format version " +
           s"for partition $topicPartition is ${config.messageFormatVersion} which is earlier than the minimum " +
           s"required version $KAFKA_0_10_0_IV0")

       // Cache to avoid race conditions. `toBuffer` is faster than most alternatives and provides
       // constant time access while being safe to use with concurrent collections unlike `toArray`.
       val segmentsCopy = logSegments.toBuffer
       // For the earliest and latest, we do not need to return the timestamp.
       if (targetTimestamp == ListOffsetRequest.EARLIEST_TIMESTAMP) {
         // The first cached epoch usually corresponds to the log start offset, but we have to verify this since
         // it may not be true following a message format version bump as the epoch will not be available for
         // log entries written in the older format.
         val earliestEpochEntry = leaderEpochCache.flatMap(_.earliestEntry)
         val epochOpt = earliestEpochEntry match {
           case Some(entry) if entry.startOffset <= logStartOffset => Optional.of[Integer](entry.epoch)
           case _ => Optional.empty[Integer]()
         }
         return Some(new TimestampAndOffset(RecordBatch.NO_TIMESTAMP, logStartOffset, epochOpt))
       } else if (targetTimestamp == ListOffsetRequest.LATEST_TIMESTAMP) {
         val latestEpochOpt = leaderEpochCache.flatMap(_.latestEpoch).map(_.asInstanceOf[Integer])
         val epochOptional = Optional.ofNullable(latestEpochOpt.orNull)
         return Some(new TimestampAndOffset(RecordBatch.NO_TIMESTAMP, logEndOffset, epochOptional))
       }

       val targetSeg = {
         // Get all the segments whose largest timestamp is smaller than target timestamp
         val earlierSegs = segmentsCopy.takeWhile(_.largestTimestamp < targetTimestamp)
         // We need to search the first segment whose largest timestamp is greater than the target timestamp if there is one.
         if (earlierSegs.length < segmentsCopy.length)
           Some(segmentsCopy(earlierSegs.length))
         else
           None
       }

       targetSeg.flatMap(_.findOffsetByTimestamp(targetTimestamp, logStartOffset))
     }
   }

   def legacyFetchOffsetsBefore(timestamp: Long, maxNumOffsets: Int): Seq[Long] = {
     // Cache to avoid race conditions. `toBuffer` is faster than most alternatives and provides
     // constant time access while being safe to use with concurrent collections unlike `toArray`.
     val segments = logSegments.toBuffer
     val lastSegmentHasSize = segments.last.size > 0

     val offsetTimeArray =
       if (lastSegmentHasSize)
         new Array[(Long, Long)](segments.length + 1)
       else
         new Array[(Long, Long)](segments.length)

     for (i <- segments.indices)
       offsetTimeArray(i) = (math.max(segments(i).baseOffset, logStartOffset), segments(i).lastModified)
     if (lastSegmentHasSize)
       offsetTimeArray(segments.length) = (logEndOffset, time.milliseconds)

     var startIndex = -1
     timestamp match {
       case ListOffsetRequest.LATEST_TIMESTAMP =>
         startIndex = offsetTimeArray.length - 1
       case ListOffsetRequest.EARLIEST_TIMESTAMP =>
         startIndex = 0
       case _ =>
         var isFound = false
         debug("Offset time array = " + offsetTimeArray.foreach(o => "%d, %d".format(o._1, o._2)))
         startIndex = offsetTimeArray.length - 1
         while (startIndex >= 0 && !isFound) {
           if (offsetTimeArray(startIndex)._2 <= timestamp)
             isFound = true
           else
             startIndex -= 1
         }
     }

     val retSize = maxNumOffsets.min(startIndex + 1)
     val ret = new Array[Long](retSize)
     for (j <- 0 until retSize) {
       ret(j) = offsetTimeArray(startIndex)._1
       startIndex -= 1
     }
     // ensure that the returned seq is in descending order of offsets
     ret.toSeq.sortBy(-_)
   }

   /**
    * Given a message offset, find its corresponding offset metadata in the log.
    * If the message offset is out of range, return None to the caller.
    */
   def convertToOffsetMetadata(offset: Long): Option[LogOffsetMetadata] = {
     try {
       val fetchDataInfo = read(offset,
         maxLength = 1,
         maxOffset = None,
         minOneMessage = false,
         includeAbortedTxns = false)
       Some(fetchDataInfo.fetchOffsetMetadata)
     } catch {
       case _: OffsetOutOfRangeException => None
     }
   }

   /**
    * Delete any log segments matching the given predicate function,
    * starting with the oldest segment and moving forward until a segment doesn't match.
    *
    * @param predicate A function that takes in a candidate log segment and the next higher segment
    *                  (if there is one) and returns true iff it is deletable
    * @return The number of segments deleted
    */
   private def deleteOldSegments(predicate: (LogSegment, Option[LogSegment]) => Boolean, reason: String): Int = {
     lock synchronized {
       val deletable = deletableSegments(predicate)
       if (deletable.nonEmpty)
         info(s"Found deletable segments with base offsets [${deletable.map(_.baseOffset).mkString(",")}] due to $reason")
       deleteSegments(deletable)
     }
   }

   private def deleteSegments(deletable: Iterable[LogSegment]): Int = {
     maybeHandleIOException(s"Error while deleting segments for $topicPartition in dir ${dir.getParent}") {
       val numToDelete = deletable.size
       if (numToDelete > 0) {
         // we must always have at least one segment, so if we are going to delete all the segments, create a new one first
         if (segments.size == numToDelete)
           roll()
         lock synchronized {
           checkIfMemoryMappedBufferClosed()
           // remove the segments for lookups
           deletable.foreach(deleteSegment)
           maybeIncrementLogStartOffset(segments.firstEntry.getValue.baseOffset)
         }
       }
       numToDelete
     }
   }

   /**
    * Find segments starting from the oldest until the user-supplied predicate is false or the segment
    * containing the current high watermark is reached. We do not delete segments with offsets at or beyond
    * the high watermark to ensure that the log start offset can never exceed it. If the high watermark
    * has not yet been initialized, no segments are eligible for deletion.
    *
    * A final segment that is empty will never be returned (since we would just end up re-creating it).
    *
    * @param predicate A function that takes in a candidate log segment and the next higher segment
    *                  (if there is one) and returns true iff it is deletable
    * @return the segments ready to be deleted
    */
   private def deletableSegments(predicate: (LogSegment, Option[LogSegment]) => Boolean): Iterable[LogSegment] = {
     if (segments.isEmpty || replicaHighWatermark.isEmpty) {
       Seq.empty
     } else {
       val highWatermark = replicaHighWatermark.get
       val deletable = ArrayBuffer.empty[LogSegment]
       var segmentEntry = segments.firstEntry
       while (segmentEntry != null) {
         val segment = segmentEntry.getValue
         val nextSegmentEntry = segments.higherEntry(segmentEntry.getKey)
         val (nextSegment, upperBoundOffset, isLastSegmentAndEmpty) = if (nextSegmentEntry != null)
           (nextSegmentEntry.getValue, nextSegmentEntry.getValue.baseOffset, false)
         else
           (null, logEndOffset, segment.size == 0)

         if (highWatermark >= upperBoundOffset && predicate(segment, Option(nextSegment)) && !isLastSegmentAndEmpty) {
           deletable += segment
           segmentEntry = nextSegmentEntry
         } else {
           segmentEntry = null
         }
       }
       deletable
     }
   }

   /**
    * If topic deletion is enabled, delete any log segments that have either expired due to time based retention
    * or because the log size is > retentionSize.
    *
    * Whether or not deletion is enabled, delete any log segments that are before the log start offset
    */
   def deleteOldSegments(): Int = {
     if (config.delete) {
       deleteRetentionMsBreachedSegments() + deleteRetentionSizeBreachedSegments() + deleteLogStartOffsetBreachedSegments()
     } else {
       deleteLogStartOffsetBreachedSegments()
     }
   }

   private def deleteRetentionMsBreachedSegments(): Int = {
     if (config.retentionMs < 0) return 0
     val startMs = time.milliseconds
     deleteOldSegments((segment, _) => startMs - segment.largestTimestamp > config.retentionMs,
       reason = s"retention time ${config.retentionMs}ms breach")
   }

   private def deleteRetentionSizeBreachedSegments(): Int = {
     if (config.retentionSize < 0 || size < config.retentionSize) return 0
     var diff = size - config.retentionSize
     def shouldDelete(segment: LogSegment, nextSegmentOpt: Option[LogSegment]) = {
       if (diff - segment.size >= 0) {
         diff -= segment.size
         true
       } else {
         false
       }
     }

     deleteOldSegments(shouldDelete, reason = s"retention size in bytes ${config.retentionSize} breach")
   }

   private def deleteLogStartOffsetBreachedSegments(): Int = {
     def shouldDelete(segment: LogSegment, nextSegmentOpt: Option[LogSegment]) =
       nextSegmentOpt.exists(_.baseOffset <= logStartOffset)

     deleteOldSegments(shouldDelete, reason = s"log start offset $logStartOffset breach")
   }

   def isFuture: Boolean = dir.getName.endsWith(Log.FutureDirSuffix)

   /**
    * The size of the log in bytes
    */
   def size: Long = Log.sizeInBytes(logSegments)

   /**
    * The offset metadata of the next message that will be appended to the log
    */
   def logEndOffsetMetadata: LogOffsetMetadata = nextOffsetMetadata

   /**
    * The offset of the next message that will be appended to the log
    */
   def logEndOffset: Long = nextOffsetMetadata.messageOffset

   /**
    * Roll the log over to a new empty log segment if necessary.
    *
    * @param messagesSize The messages set size in bytes.
    * @param appendInfo log append information
    * logSegment will be rolled if one of the following conditions met
    * <ol>
    * <li> The logSegment is full
    * <li> The maxTime has elapsed since the timestamp of first message in the segment (or since the create time if
    * the first message does not have a timestamp)
    * <li> The index is full
    * </ol>
    * @return The currently active segment after (perhaps) rolling to a new segment
    */
   private def maybeRoll(messagesSize: Int, appendInfo: LogAppendInfo): LogSegment = {
     val segment = activeSegment
     val now = time.milliseconds

     val maxTimestampInMessages = appendInfo.maxTimestamp
     val maxOffsetInMessages = appendInfo.lastOffset

     if (segment.shouldRoll(RollParams(config, appendInfo, messagesSize, now))) {
       debug(s"Rolling new log segment (log_size = ${segment.size}/${config.segmentSize}}, " +
         s"offset_index_size = ${segment.offsetIndex.entries}/${segment.offsetIndex.maxEntries}, " +
         s"time_index_size = ${segment.timeIndex.entries}/${segment.timeIndex.maxEntries}, " +
         s"inactive_time_ms = ${segment.timeWaitedForRoll(now, maxTimestampInMessages)}/${config.segmentMs - segment.rollJitterMs}).")

       /*
         maxOffsetInMessages - Integer.MAX_VALUE is a heuristic value for the first offset in the set of messages.
         Since the offset in messages will not differ by more than Integer.MAX_VALUE, this is guaranteed <= the real
         first offset in the set. Determining the true first offset in the set requires decompression, which the follower
         is trying to avoid during log append. Prior behavior assigned new baseOffset = logEndOffset from old segment.
         This was problematic in the case that two consecutive messages differed in offset by
         Integer.MAX_VALUE.toLong + 2 or more.  In this case, the prior behavior would roll a new log segment whose
         base offset was too low to contain the next message.  This edge case is possible when a replica is recovering a
         highly compacted topic from scratch.
         Note that this is only required for pre-V2 message formats because these do not store the first message offset
         in the header.
       */
       appendInfo.firstOffset match {
         case Some(firstOffset) => roll(Some(firstOffset))
         case None => roll(Some(maxOffsetInMessages - Integer.MAX_VALUE))
       }
     } else {
       segment
     }
   }

   /**
    * Roll the log over to a new active segment starting with the current logEndOffset.
    * This will trim the index to the exact size of the number of entries it currently contains.
    *
    * @return The newly rolled segment
    */
   def roll(expectedNextOffset: Option[Long] = None): LogSegment = {
     maybeHandleIOException(s"Error while rolling log segment for $topicPartition in dir ${dir.getParent}") {
       val start = time.hiResClockMs()
       lock synchronized {
         checkIfMemoryMappedBufferClosed()
         val newOffset = math.max(expectedNextOffset.getOrElse(0L), logEndOffset)
         val logFile = Log.logFile(dir, newOffset)

         if (segments.containsKey(newOffset)) {
           // segment with the same base offset already exists and loaded
           if (activeSegment.baseOffset == newOffset && activeSegment.size == 0) {
             // We have seen this happen (see KAFKA-6388) after shouldRoll() returns true for an
             // active segment of size zero because of one of the indexes is "full" (due to _maxEntries == 0).
             warn(s"Trying to roll a new log segment with start offset $newOffset " +
                  s"=max(provided offset = $expectedNextOffset, LEO = $logEndOffset) while it already " +
                  s"exists and is active with size 0. Size of time index: ${activeSegment.timeIndex.entries}," +
                  s" size of offset index: ${activeSegment.offsetIndex.entries}.")
             deleteSegment(activeSegment)
           } else {
             throw new KafkaException(s"Trying to roll a new log segment for topic partition $topicPartition with start offset $newOffset" +
                                      s" =max(provided offset = $expectedNextOffset, LEO = $logEndOffset) while it already exists. Existing " +
                                      s"segment is ${segments.get(newOffset)}.")
           }
         } else if (!segments.isEmpty && newOffset < activeSegment.baseOffset) {
           throw new KafkaException(
             s"Trying to roll a new log segment for topic partition $topicPartition with " +
             s"start offset $newOffset =max(provided offset = $expectedNextOffset, LEO = $logEndOffset) lower than start offset of the active segment $activeSegment")
         } else {
           val offsetIdxFile = offsetIndexFile(dir, newOffset)
           val timeIdxFile = timeIndexFile(dir, newOffset)
           val txnIdxFile = transactionIndexFile(dir, newOffset)

           for (file <- List(logFile, offsetIdxFile, timeIdxFile, txnIdxFile) if file.exists) {
             warn(s"Newly rolled segment file ${file.getAbsolutePath} already exists; deleting it first")
             Files.delete(file.toPath)
           }

           Option(segments.lastEntry).foreach(_.getValue.onBecomeInactiveSegment())
         }

         // take a snapshot of the producer state to facilitate recovery. It is useful to have the snapshot
         // offset align with the new segment offset since this ensures we can recover the segment by beginning
         // with the corresponding snapshot file and scanning the segment data. Because the segment base offset
         // may actually be ahead of the current producer state end offset (which corresponds to the log end offset),
         // we manually override the state offset here prior to taking the snapshot.
         producerStateManager.updateMapEndOffset(newOffset)
         producerStateManager.takeSnapshot()

         val segment = LogSegment.open(dir,
           baseOffset = newOffset,
           config,
           time = time,
           fileAlreadyExists = false,
           initFileSize = initFileSize,
           preallocate = config.preallocate)
         addSegment(segment)
         // We need to update the segment base offset and append position data of the metadata when log rolls.
         // The next offset should not change.
         updateLogEndOffset(nextOffsetMetadata.messageOffset)
         // schedule an asynchronous flush of the old segment
         scheduler.schedule("flush-log", () => flush(newOffset), delay = 0L)

         info(s"Rolled new log segment at offset $newOffset in ${time.hiResClockMs() - start} ms.")

         segment
       }
     }
   }

   /**
    * The number of messages appended to the log since the last flush
    */
   def unflushedMessages: Long = this.logEndOffset - this.recoveryPoint

   /**
    * Flush all log segments
    */
   def flush(): Unit = flush(this.logEndOffset)

   /**
    * Flush log segments for all offsets up to offset-1
    *
    * @param offset The offset to flush up to (non-inclusive); the new recovery point
    */
   def flush(offset: Long) : Unit = {
     maybeHandleIOException(s"Error while flushing log for $topicPartition in dir ${dir.getParent} with offset $offset") {
       if (offset <= this.recoveryPoint)
         return
       debug(s"Flushing log up to offset $offset, last flushed: $lastFlushTime,  current time: ${time.milliseconds()}, " +
         s"unflushed: $unflushedMessages")
       for (segment <- logSegments(this.recoveryPoint, offset))
         segment.flush()

       lock synchronized {
         checkIfMemoryMappedBufferClosed()
         if (offset > this.recoveryPoint) {
           this.recoveryPoint = offset
           lastFlushedTime.set(time.milliseconds)
         }
       }
     }
   }

   /**
    * Cleanup old producer snapshots after the recovery point is checkpointed. It is useful to retain
    * the snapshots from the recent segments in case we need to truncate and rebuild the producer state.
    * Otherwise, we would always need to rebuild from the earliest segment.
    *
    * More specifically:
    *
    * 1. We always retain the producer snapshot from the last two segments. This solves the common case
    * of truncating to an offset within the active segment, and the rarer case of truncating to the previous segment.
    *
    * 2. We only delete snapshots for offsets less than the recovery point. The recovery point is checkpointed
    * periodically and it can be behind after a hard shutdown. Since recovery starts from the recovery point, the logic
    * of rebuilding the producer snapshots in one pass and without loading older segments is simpler if we always
    * have a producer snapshot for all segments being recovered.
    *
    * Return the minimum snapshots offset that was retained.
    */
   def deleteSnapshotsAfterRecoveryPointCheckpoint(): Long = {
     val minOffsetToRetain = minSnapshotsOffsetToRetain
     producerStateManager.deleteSnapshotsBefore(minOffsetToRetain)
     minOffsetToRetain
   }

   // Visible for testing, see `deleteSnapshotsAfterRecoveryPointCheckpoint()` for details
   private[log] def minSnapshotsOffsetToRetain: Long = {
     lock synchronized {
       val twoSegmentsMinOffset = lowerSegment(activeSegment.baseOffset).getOrElse(activeSegment).baseOffset
       // Prefer segment base offset
       val recoveryPointOffset = lowerSegment(recoveryPoint).map(_.baseOffset).getOrElse(recoveryPoint)
       math.min(recoveryPointOffset, twoSegmentsMinOffset)
     }
   }

   private def lowerSegment(offset: Long): Option[LogSegment] =
     Option(segments.lowerEntry(offset)).map(_.getValue)

   /**
    * Completely delete this log directory and all contents from the file system with no delay
    */
   private[log] def delete() {
     maybeHandleIOException(s"Error while deleting log for $topicPartition in dir ${dir.getParent}") {
       lock synchronized {
         checkIfMemoryMappedBufferClosed()
         removeLogMetrics()
         logSegments.foreach(_.deleteIfExists())
         segments.clear()
         leaderEpochCache.foreach(_.clear())
         Utils.delete(dir)
         // File handlers will be closed if this log is deleted
         isMemoryMappedBufferClosed = true
       }
     }
   }

   // visible for testing
   private[log] def takeProducerSnapshot(): Unit = lock synchronized {
     checkIfMemoryMappedBufferClosed()
     producerStateManager.takeSnapshot()
   }

   // visible for testing
   private[log] def latestProducerSnapshotOffset: Option[Long] = lock synchronized {
     producerStateManager.latestSnapshotOffset
   }

   // visible for testing
   private[log] def oldestProducerSnapshotOffset: Option[Long] = lock synchronized {
     producerStateManager.oldestSnapshotOffset
   }

   // visible for testing
   private[log] def latestProducerStateEndOffset: Long = lock synchronized {
     producerStateManager.mapEndOffset
   }

   /**
    * Truncate this log so that it ends with the greatest offset < targetOffset.
    *
    * @param targetOffset The offset to truncate to, an upper bound on all offsets in the log after truncation is complete.
    * @return True iff targetOffset < logEndOffset
    */
   private[log] def truncateTo(targetOffset: Long): Boolean = {
     maybeHandleIOException(s"Error while truncating log to offset $targetOffset for $topicPartition in dir ${dir.getParent}") {
       if (targetOffset < 0)
         throw new IllegalArgumentException(s"Cannot truncate partition $topicPartition to a negative offset (%d).".format(targetOffset))
       if (targetOffset >= logEndOffset) {
         info(s"Truncating to $targetOffset has no effect as the largest offset in the log is ${logEndOffset - 1}")
         false
       } else {
         info(s"Truncating to offset $targetOffset")
         lock synchronized {
           checkIfMemoryMappedBufferClosed()
           if (segments.firstEntry.getValue.baseOffset > targetOffset) {
             truncateFullyAndStartAt(targetOffset)
           } else {
             val deletable = logSegments.filter(segment => segment.baseOffset > targetOffset)
             deletable.foreach(deleteSegment)
             activeSegment.truncateTo(targetOffset)
             updateLogEndOffset(targetOffset)
             this.recoveryPoint = math.min(targetOffset, this.recoveryPoint)
             this.logStartOffset = math.min(targetOffset, this.logStartOffset)
             leaderEpochCache.foreach(_.truncateFromEnd(targetOffset))
             loadProducerState(targetOffset, reloadFromCleanShutdown = false)
           }
           true
         }
       }
     }
   }

   /**
    *  Delete all data in the log and start at the new offset
    *
    *  @param newOffset The new offset to start the log with
    */
   private[log] def truncateFullyAndStartAt(newOffset: Long) {
     maybeHandleIOException(s"Error while truncating the entire log for $topicPartition in dir ${dir.getParent}") {
       debug(s"Truncate and start at offset $newOffset")
       lock synchronized {
         checkIfMemoryMappedBufferClosed()
         val segmentsToDelete = logSegments.toList
         segmentsToDelete.foreach(deleteSegment)
         addSegment(LogSegment.open(dir,
           baseOffset = newOffset,
           config = config,
           time = time,
           fileAlreadyExists = false,
           initFileSize = initFileSize,
           preallocate = config.preallocate))
         updateLogEndOffset(newOffset)
         leaderEpochCache.foreach(_.clearAndFlush())

         producerStateManager.truncate()
         producerStateManager.updateMapEndOffset(newOffset)
         updateFirstUnstableOffset()

         this.recoveryPoint = math.min(newOffset, this.recoveryPoint)
         this.logStartOffset = newOffset
       }
     }
   }

   /**
    * The time this log is last known to have been fully flushed to disk
    */
   def lastFlushTime: Long = lastFlushedTime.get

   /**
    * The active segment that is currently taking appends
    */
   def activeSegment = segments.lastEntry.getValue

   /**
    * All the log segments in this log ordered from oldest to newest
    */
   def logSegments: Iterable[LogSegment] = segments.values.asScala

   /**
    * Get all segments beginning with the segment that includes "from" and ending with the segment
    * that includes up to "to-1" or the end of the log (if to > logEndOffset)
    */
   def logSegments(from: Long, to: Long): Iterable[LogSegment] = {
     lock synchronized {
       val view = Option(segments.floorKey(from)).map { floor =>
         segments.subMap(floor, to)
       }.getOrElse(segments.headMap(to))
       view.values.asScala
     }
   }

   override def toString = "Log(" + dir + ")"

   /**
    * This method performs an asynchronous log segment delete by doing the following:
    * <ol>
    *   <li>It removes the segment from the segment map so that it will no longer be used for reads.
    *   <li>It renames the index and log files by appending .deleted to the respective file name
    *   <li>It schedules an asynchronous delete operation to occur in the future
    * </ol>
    * This allows reads to happen concurrently without synchronization and without the possibility of physically
    * deleting a file while it is being read from.
    *
    * This method does not need to convert IOException to KafkaStorageException because it is either called before all logs are loaded
    * or the immediate caller will catch and handle IOException
    *
    * @param segment The log segment to schedule for deletion
    */
   private def deleteSegment(segment: LogSegment) {
     info(s"Scheduling log segment [baseOffset ${segment.baseOffset}, size ${segment.size}] for deletion.")
     lock synchronized {
       segments.remove(segment.baseOffset)
       asyncDeleteSegment(segment)
     }
   }

   /**
    * Perform an asynchronous delete on the given file.
    *
    * This method assumes that the file exists and the method is not thread-safe.
    *
    * This method does not need to convert IOException (thrown from changeFileSuffixes) to KafkaStorageException because
    * it is either called before all logs are loaded or the caller will catch and handle IOException
    *
    * @throws IOException if the file can't be renamed and still exists
    */
   private def asyncDeleteSegment(segment: LogSegment) {
     segment.changeFileSuffixes("", Log.DeletedFileSuffix)
     def deleteSeg() {
       info(s"Deleting segment ${segment.baseOffset}")
       maybeHandleIOException(s"Error while deleting segments for $topicPartition in dir ${dir.getParent}") {
         segment.deleteIfExists()
       }
     }
     scheduler.schedule("delete-file", deleteSeg _, delay = config.fileDeleteDelayMs)
   }

   /**
    * Swap one or more new segment in place and delete one or more existing segments in a crash-safe manner. The old
    * segments will be asynchronously deleted.
    *
    * This method does not need to convert IOException to KafkaStorageException because it is either called before all logs are loaded
    * or the caller will catch and handle IOException
    *
    * The sequence of operations is:
    * <ol>
    *   <li> Cleaner creates one or more new segments with suffix .cleaned and invokes replaceSegments().
    *        If broker crashes at this point, the clean-and-swap operation is aborted and
    *        the .cleaned files are deleted on recovery in loadSegments().
    *   <li> New segments are renamed .swap. If the broker crashes before all segments were renamed to .swap, the
    *        clean-and-swap operation is aborted - .cleaned as well as .swap files are deleted on recovery in
    *        loadSegments(). We detect this situation by maintaining a specific order in which files are renamed from
    *        .cleaned to .swap. Basically, files are renamed in descending order of offsets. On recovery, all .swap files
    *        whose offset is greater than the minimum-offset .clean file are deleted.
    *   <li> If the broker crashes after all new segments were renamed to .swap, the operation is completed, the swap
    *        operation is resumed on recovery as described in the next step.
    *   <li> Old segment files are renamed to .deleted and asynchronous delete is scheduled.
    *        If the broker crashes, any .deleted files left behind are deleted on recovery in loadSegments().
    *        replaceSegments() is then invoked to complete the swap with newSegment recreated from
    *        the .swap file and oldSegments containing segments which were not renamed before the crash.
    *   <li> Swap segment(s) are renamed to replace the existing segments, completing this operation.
    *        If the broker crashes, any .deleted files which may be left behind are deleted
    *        on recovery in loadSegments().
    * </ol>
    *
    * @param newSegments The new log segment to add to the log
    * @param oldSegments The old log segments to delete from the log
    * @param isRecoveredSwapFile true if the new segment was created from a swap file during recovery after a crash
    */
   private[log] def replaceSegments(newSegments: Seq[LogSegment], oldSegments: Seq[LogSegment], isRecoveredSwapFile: Boolean = false) {
     lock synchronized {
       val sortedNewSegments = newSegments.sortBy(_.baseOffset)
       // Some old segments may have been removed from index and scheduled for async deletion after the caller reads segments
       // but before this method is executed. We want to filter out those segments to avoid calling asyncDeleteSegment()
       // multiple times for the same segment.
       val sortedOldSegments = oldSegments.filter(seg => segments.containsKey(seg.baseOffset)).sortBy(_.baseOffset)

       checkIfMemoryMappedBufferClosed()
       // need to do this in two phases to be crash safe AND do the delete asynchronously
       // if we crash in the middle of this we complete the swap in loadSegments()
       if (!isRecoveredSwapFile)
         sortedNewSegments.reverse.foreach(_.changeFileSuffixes(Log.CleanedFileSuffix, Log.SwapFileSuffix))
       sortedNewSegments.reverse.foreach(addSegment(_))

       // delete the old files
       for (seg <- sortedOldSegments) {
         // remove the index entry
         if (seg.baseOffset != sortedNewSegments.head.baseOffset)
           segments.remove(seg.baseOffset)
         // delete segment
         asyncDeleteSegment(seg)
       }
       // okay we are safe now, remove the swap suffix
       sortedNewSegments.foreach(_.changeFileSuffixes(Log.SwapFileSuffix, ""))
     }
   }

   /**
     * This function does not acquire Log.lock. The caller has to make sure log segments don't get deleted during
     * this call, and also protects against calling this function on the same segment in parallel.
     *
     * Currently, it is used by LogCleaner threads on log compact non-active segments only with LogCleanerManager's lock
     * to ensure no other logcleaner threads and retention thread can work on the same segment.
     */
   private[log] def getFirstBatchTimestampForSegments(segments: Iterable[LogSegment]): Iterable[Long] = {
     segments.map {
       segment =>
         segment.getFirstBatchTimestamp()
     }
   }

   /**
    * remove deleted log metrics
    */
   private[log] def removeLogMetrics(): Unit = {
     removeMetric("NumLogSegments", tags)
     removeMetric("LogStartOffset", tags)
     removeMetric("LogEndOffset", tags)
     removeMetric("Size", tags)
   }

   /**
    * Add the given segment to the segments in this log. If this segment replaces an existing segment, delete it.
    * @param segment The segment to add
    */
   @threadsafe
   def addSegment(segment: LogSegment): LogSegment = this.segments.put(segment.baseOffset, segment)

   private def maybeHandleIOException[T](msg: => String)(fun: => T): T = {
     try {
       fun
     } catch {
       case e: IOException =>
         logDirFailureChannel.maybeAddOfflineLogDir(dir.getParent, msg, e)
         throw new KafkaStorageException(msg, e)
     }
   }

   private[log] def retryOnOffsetOverflow[T](fn: => T): T = {
     while (true) {
       try {
         return fn
       } catch {
         case e: LogSegmentOffsetOverflowException =>
           info(s"Caught segment overflow error: ${e.getMessage}. Split segment and retry.")
           splitOverflowedSegment(e.segment)
       }
     }
     throw new IllegalStateException()
   }

   /**
    * Split a segment into one or more segments such that there is no offset overflow in any of them. The
    * resulting segments will contain the exact same messages that are present in the input segment. On successful
    * completion of this method, the input segment will be deleted and will be replaced by the resulting new segments.
    * See replaceSegments for recovery logic, in case the broker dies in the middle of this operation.
    * <p>Note that this method assumes we have already determined that the segment passed in contains records that cause
    * offset overflow.</p>
    * <p>The split logic overloads the use of .clean files that LogCleaner typically uses to make the process of replacing
    * the input segment with multiple new segments atomic and recoverable in the event of a crash. See replaceSegments
    * and completeSwapOperations for the implementation to make this operation recoverable on crashes.</p>
    * @param segment Segment to split
    * @return List of new segments that replace the input segment
    */
   private[log] def splitOverflowedSegment(segment: LogSegment): List[LogSegment] = {
     require(isLogFile(segment.log.file), s"Cannot split file ${segment.log.file.getAbsoluteFile}")
     require(segment.hasOverflow, "Split operation is only permitted for segments with overflow")

     info(s"Splitting overflowed segment $segment")

     val newSegments = ListBuffer[LogSegment]()
     try {
       var position = 0
       val sourceRecords = segment.log

       while (position < sourceRecords.sizeInBytes) {
         val firstBatch = sourceRecords.batchesFrom(position).asScala.head
         val newSegment = LogCleaner.createNewCleanedSegment(this, firstBatch.baseOffset)
         newSegments += newSegment

         val bytesAppended = newSegment.appendFromFile(sourceRecords, position)
         if (bytesAppended == 0)
           throw new IllegalStateException(s"Failed to append records from position $position in $segment")

         position += bytesAppended
       }

       // prepare new segments
       var totalSizeOfNewSegments = 0
       newSegments.foreach { splitSegment =>
         splitSegment.onBecomeInactiveSegment()
         splitSegment.flush()
         splitSegment.lastModified = segment.lastModified
         totalSizeOfNewSegments += splitSegment.log.sizeInBytes
       }
       // size of all the new segments combined must equal size of the original segment
       if (totalSizeOfNewSegments != segment.log.sizeInBytes)
         throw new IllegalStateException("Inconsistent segment sizes after split" +
           s" before: ${segment.log.sizeInBytes} after: $totalSizeOfNewSegments")

       // replace old segment with new ones
       info(s"Replacing overflowed segment $segment with split segments $newSegments")
       replaceSegments(newSegments.toList, List(segment), isRecoveredSwapFile = false)
       newSegments.toList
     } catch {
       case e: Exception =>
         newSegments.foreach { splitSegment =>
           splitSegment.close()
           splitSegment.deleteIfExists()
         }
         throw e
     }
   }
 }

 /**
  * Helper functions for logs
  */
 object Log {

   /** a log file */
   val LogFileSuffix = ".log"

   /** an index file */
   val IndexFileSuffix = ".index"

   /** a time index file */
   val TimeIndexFileSuffix = ".timeindex"

   val ProducerSnapshotFileSuffix = ".snapshot"

   /** an (aborted) txn index */
   val TxnIndexFileSuffix = ".txnindex"

   /** a file that is scheduled to be deleted */
   val DeletedFileSuffix = ".deleted"

   /** A temporary file that is being used for log cleaning */
   val CleanedFileSuffix = ".cleaned"

   /** A temporary file used when swapping files into the log */
   val SwapFileSuffix = ".swap"

   /** Clean shutdown file that indicates the broker was cleanly shutdown in 0.8 and higher.
    * This is used to avoid unnecessary recovery after a clean shutdown. In theory this could be
    * avoided by passing in the recovery point, however finding the correct position to do this
    * requires accessing the offset index which may not be safe in an unclean shutdown.
    * For more information see the discussion in PR#2104
    */
   val CleanShutdownFile = ".kafka_cleanshutdown"

   /** a directory that is scheduled to be deleted */
   val DeleteDirSuffix = "-delete"

   /** a directory that is used for future partition */
   val FutureDirSuffix = "-future"

   private[log] val DeleteDirPattern = Pattern.compile(s"^(\\S+)-(\\S+)\\.(\\S+)$DeleteDirSuffix")
   private[log] val FutureDirPattern = Pattern.compile(s"^(\\S+)-(\\S+)\\.(\\S+)$FutureDirSuffix")

   val UnknownLogStartOffset = -1L

   def apply(dir: File,
             config: LogConfig,
             logStartOffset: Long,
             recoveryPoint: Long,
             scheduler: Scheduler,
             brokerTopicStats: BrokerTopicStats,
             time: Time = Time.SYSTEM,
             maxProducerIdExpirationMs: Int,
             producerIdExpirationCheckIntervalMs: Int,
             logDirFailureChannel: LogDirFailureChannel): Log = {
     val topicPartition = Log.parseTopicPartitionName(dir)
     val producerStateManager = new ProducerStateManager(topicPartition, dir, maxProducerIdExpirationMs)
     new Log(dir, config, logStartOffset, recoveryPoint, scheduler, brokerTopicStats, time, maxProducerIdExpirationMs,
       producerIdExpirationCheckIntervalMs, topicPartition, producerStateManager, logDirFailureChannel)
   }

   /**
    * Make log segment file name from offset bytes. All this does is pad out the offset number with zeros
    * so that ls sorts the files numerically.
    *
    * @param offset The offset to use in the file name
    * @return The filename
    */
   def filenamePrefixFromOffset(offset: Long): String = {
     val nf = NumberFormat.getInstance()
     nf.setMinimumIntegerDigits(20)
     nf.setMaximumFractionDigits(0)
     nf.setGroupingUsed(false)
     nf.format(offset)
   }

   /**
    * Construct a log file name in the given dir with the given base offset and the given suffix
    *
    * @param dir The directory in which the log will reside
    * @param offset The base offset of the log file
    * @param suffix The suffix to be appended to the file name (e.g. "", ".deleted", ".cleaned", ".swap", etc.)
    */
   def logFile(dir: File, offset: Long, suffix: String = ""): File =
     new File(dir, filenamePrefixFromOffset(offset) + LogFileSuffix + suffix)

   /**
    * Return a directory name to rename the log directory to for async deletion.
    * The name will be in the following format: "topic-partitionId.uniqueId-delete".
    * If the topic name is too long, it will be truncated to prevent the total name
    * from exceeding 255 characters.
    */
   def logDeleteDirName(topicPartition: TopicPartition): String = {
     val uniqueId = java.util.UUID.randomUUID.toString.replaceAll("-", "")
     val suffix = s"-${topicPartition.partition()}.${uniqueId}${DeleteDirSuffix}"
     val prefixLength = Math.min(topicPartition.topic().size, 255 - suffix.size)
     s"${topicPartition.topic().substring(0, prefixLength)}${suffix}"
   }

   /**
    * Return a future directory name for the given topic partition. The name will be in the following
    * format: topic-partition.uniqueId-future where topic, partition and uniqueId are variables.
    */
   def logFutureDirName(topicPartition: TopicPartition): String = {
     logDirNameWithSuffix(topicPartition, FutureDirSuffix)
   }

   private def logDirNameWithSuffix(topicPartition: TopicPartition, suffix: String): String = {
     val uniqueId = java.util.UUID.randomUUID.toString.replaceAll("-", "")
     s"${logDirName(topicPartition)}.$uniqueId$suffix"
   }

   /**
    * Return a directory name for the given topic partition. The name will be in the following
    * format: topic-partition where topic, partition are variables.
    */
   def logDirName(topicPartition: TopicPartition): String = {
     s"${topicPartition.topic}-${topicPartition.partition}"
   }

   /**
    * Construct an index file name in the given dir using the given base offset and the given suffix
    *
    * @param dir The directory in which the log will reside
    * @param offset The base offset of the log file
    * @param suffix The suffix to be appended to the file name ("", ".deleted", ".cleaned", ".swap", etc.)
    */
   def offsetIndexFile(dir: File, offset: Long, suffix: String = ""): File =
     new File(dir, filenamePrefixFromOffset(offset) + IndexFileSuffix + suffix)

   /**
    * Construct a time index file name in the given dir using the given base offset and the given suffix
    *
    * @param dir The directory in which the log will reside
    * @param offset The base offset of the log file
    * @param suffix The suffix to be appended to the file name ("", ".deleted", ".cleaned", ".swap", etc.)
    */
   def timeIndexFile(dir: File, offset: Long, suffix: String = ""): File =
     new File(dir, filenamePrefixFromOffset(offset) + TimeIndexFileSuffix + suffix)

   def deleteFileIfExists(file: File, suffix: String = ""): Unit =
     Files.deleteIfExists(new File(file.getPath + suffix).toPath)

   /**
    * Construct a producer id snapshot file using the given offset.
    *
    * @param dir The directory in which the log will reside
    * @param offset The last offset (exclusive) included in the snapshot
    */
   def producerSnapshotFile(dir: File, offset: Long): File =
     new File(dir, filenamePrefixFromOffset(offset) + ProducerSnapshotFileSuffix)

   /**
    * Construct a transaction index file name in the given dir using the given base offset and the given suffix
    *
    * @param dir The directory in which the log will reside
    * @param offset The base offset of the log file
    * @param suffix The suffix to be appended to the file name ("", ".deleted", ".cleaned", ".swap", etc.)
    */
   def transactionIndexFile(dir: File, offset: Long, suffix: String = ""): File =
     new File(dir, filenamePrefixFromOffset(offset) + TxnIndexFileSuffix + suffix)

   def offsetFromFileName(filename: String): Long = {
     filename.substring(0, filename.indexOf('.')).toLong
   }

   def offsetFromFile(file: File): Long = {
     offsetFromFileName(file.getName)
   }

   /**
    * Calculate a log's size (in bytes) based on its log segments
    *
    * @param segments The log segments to calculate the size of
    * @return Sum of the log segments' sizes (in bytes)
    */
   def sizeInBytes(segments: Iterable[LogSegment]): Long =
     segments.map(_.size.toLong).sum

   /**
    * Parse the topic and partition out of the directory name of a log
    */
   def parseTopicPartitionName(dir: File): TopicPartition = {
     if (dir == null)
       throw new KafkaException("dir should not be null")

     def exception(dir: File): KafkaException = {
       new KafkaException(s"Found directory ${dir.getCanonicalPath}, '${dir.getName}' is not in the form of " +
         "topic-partition or topic-partition.uniqueId-delete (if marked for deletion).\n" +
         "Kafka's log directories (and children) should only contain Kafka topic data.")
     }

     val dirName = dir.getName
     if (dirName == null || dirName.isEmpty || !dirName.contains('-'))
       throw exception(dir)
     if (dirName.endsWith(DeleteDirSuffix) && !DeleteDirPattern.matcher(dirName).matches ||
         dirName.endsWith(FutureDirSuffix) && !FutureDirPattern.matcher(dirName).matches)
       throw exception(dir)

     val name: String =
       if (dirName.endsWith(DeleteDirSuffix) || dirName.endsWith(FutureDirSuffix)) dirName.substring(0, dirName.lastIndexOf('.'))
       else dirName

     val index = name.lastIndexOf('-')
     val topic = name.substring(0, index)
     val partitionString = name.substring(index + 1)
     if (topic.isEmpty || partitionString.isEmpty)
       throw exception(dir)

     val partition =
       try partitionString.toInt
       catch { case _: NumberFormatException => throw exception(dir) }

     new TopicPartition(topic, partition)
   }

   private def isIndexFile(file: File): Boolean = {
     val filename = file.getName
     filename.endsWith(IndexFileSuffix) || filename.endsWith(TimeIndexFileSuffix) || filename.endsWith(TxnIndexFileSuffix)
   }

   private def isLogFile(file: File): Boolean =
     file.getPath.endsWith(LogFileSuffix)

 }