Github user zsxwing commented on a diff in the pull request:

    https://github.com/apache/spark/pull/13513#discussion_r79518675
  
    --- Diff: 
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSourceLog.scala
 ---
    @@ -0,0 +1,133 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You under the Apache License, Version 2.0
    + * (the "License"); you may not use this file except in compliance with
    + * the License.  You may obtain a copy of the License at
    + *
    + *    http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +
    +package org.apache.spark.sql.execution.streaming
    +
    +import scala.collection.mutable
    +
    +import org.json4s.NoTypeHints
    +import org.json4s.jackson.Serialization
    +
    +import org.apache.spark.sql.SparkSession
    +import org.apache.spark.sql.execution.streaming.FileStreamSource.FileEntry
    +import org.apache.spark.sql.internal.SQLConf
    +
    +class FileStreamSourceLog(
    +    metadataLogVersion: String,
    +    sparkSession: SparkSession,
    +    path: String)
    +  extends CompactibleFileStreamLog[FileEntry](metadataLogVersion, 
sparkSession, path) {
    +
    +  import CompactibleFileStreamLog._
    +
    +  // Configurations about metadata compaction
    +  protected override val compactInterval =
    +  sparkSession.conf.get(SQLConf.FILE_SOURCE_LOG_COMPACT_INTERVAL)
    +  require(compactInterval > 0,
    +    s"Please set ${SQLConf.FILE_SOURCE_LOG_COMPACT_INTERVAL.key} (was 
$compactInterval) to a " +
    +      s"positive value.")
    +
    +  protected override val fileCleanupDelayMs =
    +    sparkSession.conf.get(SQLConf.FILE_SOURCE_LOG_CLEANUP_DELAY)
    +
    +  protected override val isDeletingExpiredLog =
    +    sparkSession.conf.get(SQLConf.FILE_SOURCE_LOG_DELETION)
    +
    +  private implicit val formats = Serialization.formats(NoTypeHints)
    +
    +  // A fixed size log cache to cache the file entries belong to the 
compaction batch. It is used
    +  // to avoid scanning the compacted log file to retrieve it's own batch 
data.
    +  private val cacheSize = compactInterval
    +  private val fileEntryCache = new mutable.LinkedHashMap[Long, 
Array[FileEntry]]
    +
    +  private def updateCache(batchId: Long, logs: Array[FileEntry]): Unit = {
    +    if (fileEntryCache.size >= cacheSize) {
    +      fileEntryCache.drop(1)
    +    }
    +
    +    fileEntryCache.put(batchId, logs)
    +  }
    +
    +  protected override def serializeData(data: FileEntry): String = {
    +    Serialization.write(data)
    +  }
    +
    +  protected override def deserializeData(encodedString: String): FileEntry 
= {
    +    Serialization.read[FileEntry](encodedString)
    +  }
    +
    +  def compactLogs(logs: Seq[FileEntry]): Seq[FileEntry] = {
    +    logs
    +  }
    +
    +  override def add(batchId: Long, logs: Array[FileEntry]): Boolean = {
    +    if (super.add(batchId, logs) && isCompactionBatch(batchId, 
compactInterval)) {
    +      updateCache(batchId, logs)
    +      true
    +    } else if (!isCompactionBatch(batchId, compactInterval)) {
    +      true
    +    } else {
    +      false
    +    }
    +  }
    +
    +  override def get(startId: Option[Long], endId: Option[Long]): 
Array[(Long, Array[FileEntry])] = {
    +    val startBatchId = startId.getOrElse(0L)
    +    val endBatchId = getLatest().map(_._1).getOrElse(0L)
    +
    +    val (existedBatches, removedBatches) = (startBatchId to 
endBatchId).map { id =>
    +      if (isCompactionBatch(id, compactInterval) && 
fileEntryCache.contains(id)) {
    +        (id, Some(fileEntryCache(id)))
    +      } else {
    +        val logs = super.get(id).map(_.filter(_.batchId == id))
    +        (id, logs)
    +      }
    +    }.partition(_._2.isDefined)
    +
    +    // The below code may only be happened when original metadata log file 
has been removed, so we
    +    // have to get the batch from latest compacted log file. This is quite 
time-consuming and may
    +    // not be happened in the current FileStreamSource code path, since we 
only fetch the
    +    // latest metadata log file.
    +    val searchKeys = removedBatches.map(_._1)
    +    val retrievedBatches = if (searchKeys.nonEmpty) {
    +      logWarning(s"Get batches from removed files, this is unexpected in 
the current code path!!!")
    +      val latestBatchId = getLatest().map(_._1).getOrElse(-1L)
    +      if (latestBatchId < 0) {
    +        Map.empty[Long, Option[Array[FileEntry]]]
    +      } else {
    +        val latestCompactedBatchId = getAllValidBatches(latestBatchId, 
compactInterval)(0)
    +        val allLogs = new mutable.HashMap[Long, 
mutable.ArrayBuffer[FileEntry]]
    +
    +        super.get(latestCompactedBatchId).foreach { entries =>
    --- End diff --
    
    Thanks for your clarifying.


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