[SPARK-15698][SQL][Streaming] Add the ability to remove the old MetadataLog in FileStreamSource

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala

@@ -0,0 +1,245 @@
+/*
+ * 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 java.io.IOException
+import java.nio.charset.StandardCharsets.UTF_8
+
+import scala.reflect.ClassTag
+
+import org.apache.hadoop.fs.{Path, PathFilter}
+
+import org.apache.spark.sql.SparkSession
+
+/**
+ * An abstract class for compactible metadata logs. It will write one log file for each batch.
+ * The first line of the log file is the version number, and there are multiple serialized
+ * metadata lines following.
+ *
+ * As reading from many small files is usually pretty slow, also too many
+ * small files in one folder will mess the FS, [[CompactibleFileStreamLog]] will
+ * compact log files every 10 batches by default into a big file. When
+ * doing a compaction, it will read all old log files and merge them with the new batch.
+ */
+abstract class CompactibleFileStreamLog[T: ClassTag](
+    metadataLogVersion: String,
+    sparkSession: SparkSession,
+    path: String)
+  extends HDFSMetadataLog[Array[T]](sparkSession, path) {
+
+  import CompactibleFileStreamLog._
+
+  /**
+   * If we delete the old files after compaction at once, there is a race condition in S3: other
+   * processes may see the old files are deleted but still cannot see the compaction file using
+   * "list". The `allFiles` handles this by looking for the next compaction file directly, however,
+   * a live lock may happen if the compaction happens too frequently: one processing keeps deleting
+   * old files while another one keeps retrying. Setting a reasonable cleanup delay could avoid it.
+   */
+  protected def fileCleanupDelayMs: Long
+
+  protected def isDeletingExpiredLog: Boolean
+
+  protected def compactInterval: Int
+
+  /**
+   * Serialize the data into encoded string.
+   */
+  protected def serializeData(t: T): String
+
+  /**
+   * Deserialize the string into data object.
+   */
+  protected def deserializeData(encodedString: String): T
+
+  /**
+   * Filter out the obsolete logs.
+   */
+  def compactLogs(logs: Seq[T]): Seq[T]
+
+  override def batchIdToPath(batchId: Long): Path = {
+    if (isCompactionBatch(batchId, compactInterval)) {
+      new Path(metadataPath, s"$batchId$COMPACT_FILE_SUFFIX")
+    } else {
+      new Path(metadataPath, batchId.toString)
+    }
+  }
+
+  override def pathToBatchId(path: Path): Long = {
+    getBatchIdFromFileName(path.getName)
+  }
+
+  override def isBatchFile(path: Path): Boolean = {
+    try {
+      getBatchIdFromFileName(path.getName)
+      true
+    } catch {
+      case _: NumberFormatException => false
+    }
+  }
+
+  override def serialize(logData: Array[T]): Array[Byte] = {
+    (metadataLogVersion +: logData.map(serializeData)).mkString("\n").getBytes(UTF_8)
+  }
+
+  override def deserialize(bytes: Array[Byte]): Array[T] = {
+    val lines = new String(bytes, UTF_8).split("\n")
+    if (lines.length == 0) {
+      throw new IllegalStateException("Incomplete log file")
+    }
+    val version = lines(0)
+    if (version != metadataLogVersion) {
+      throw new IllegalStateException(s"Unknown log version: ${version}")
+    }
+    lines.slice(1, lines.length).map(deserializeData)
+  }
+
+  override def add(batchId: Long, logs: Array[T]): Boolean = {
+    if (isCompactionBatch(batchId, compactInterval)) {
+      compact(batchId, logs)
+    } else {
+      super.add(batchId, logs)
+    }
+  }
+
+  /**
+   * Compacts all logs before `batchId` plus the provided `logs`, and writes them into the
+   * corresponding `batchId` file. It will delete expired files as well if enabled.
+   */
+  private def compact(batchId: Long, logs: Array[T]): Boolean = {
+    val validBatches = getValidBatchesBeforeCompactionBatch(batchId, compactInterval)
+    val allLogs = validBatches.flatMap(batchId => super.get(batchId)).flatten ++ logs
+    if (super.add(batchId, compactLogs(allLogs).toArray)) {
+      if (isDeletingExpiredLog) {
+        deleteExpiredLog(batchId)
+      }
+      true
+    } else {
+      // Return false as there is another writer.
+      false
+    }
+  }
+
+  /**
+   * Returns all files except the deleted ones.
+   */
+  def allFiles(): Array[T] = {
+    var latestId = getLatest().map(_._1).getOrElse(-1L)
+    // There is a race condition when `FileStreamSink` is deleting old files and `StreamFileCatalog`
+    // is calling this method. This loop will retry the reading to deal with the
+    // race condition.
+    while (true) {
+      if (latestId >= 0) {
+        try {
+          val logs =
+            getAllValidBatches(latestId, compactInterval).flatMap(id => super.get(id)).flatten
+          return compactLogs(logs).toArray
+        } catch {
+          case e: IOException =>
+            // Another process using `CompactibleFileStreamLog` may delete the batch files when
+            // `StreamFileCatalog` are reading. However, it only happens when a compaction is
+            // deleting old files. If so, let's try the next compaction batch and we should find it.
+            // Otherwise, this is a real IO issue and we should throw it.
+            latestId = nextCompactionBatchId(latestId, compactInterval)
+            super.get(latestId).getOrElse {
+              throw e
+            }
+        }
+      } else {
+        return Array.empty
+      }
+    }
+    Array.empty
+  }
+
+  /**
+   * Since all logs before `compactionBatchId` are compacted and written into the
+   * `compactionBatchId` log file, they can be removed. However, due to the eventual consistency of
+   * S3, the compaction file may not be seen by other processes at once. So we only delete files
+   * created `fileCleanupDelayMs` milliseconds ago.
+   */
+  private def deleteExpiredLog(compactionBatchId: Long): Unit = {
+    val expiredTime = System.currentTimeMillis() - fileCleanupDelayMs
+    fileManager.list(metadataPath, new PathFilter {
+      override def accept(path: Path): Boolean = {
+        try {
+          val batchId = getBatchIdFromFileName(path.getName)
+          batchId < compactionBatchId
+        } catch {
+          case _: NumberFormatException =>
+            false
+        }
+      }
+    }).foreach { f =>
+      if (f.getModificationTime <= expiredTime) {
+        fileManager.delete(f.getPath)
+      }
+    }
+  }
+}
+
+object CompactibleFileStreamLog {
+  val COMPACT_FILE_SUFFIX = ".compact"
+
+  def getBatchIdFromFileName(fileName: String): Long = {
+    fileName.stripSuffix(COMPACT_FILE_SUFFIX).toLong
+  }
+
+  /**
+   * Returns if this is a compaction batch. FileStreamSinkLog will compact old logs every
+   * `compactInterval` commits.
+   *
+   * E.g., if `compactInterval` is 3, then 2, 5, 8, ... are all compaction batches.
+   */
+  def isCompactionBatch(batchId: Long, compactInterval: Int): Boolean = {
+    (batchId + 1) % compactInterval == 0
+  }
+
+  /**
+   * Returns all valid batches before the specified `compactionBatchId`. They contain all logs we
+   * need to do a new compaction.
+   *
+   * E.g., if `compactInterval` is 3 and `compactionBatchId` is 5, this method should returns
+   * `Seq(2, 3, 4)` (Note: it includes the previous compaction batch 2).
+   */
+  def getValidBatchesBeforeCompactionBatch(
+      compactionBatchId: Long,
+      compactInterval: Int): Seq[Long] = {
+    assert(isCompactionBatch(compactionBatchId, compactInterval),
+      s"$compactionBatchId is not a compaction batch")
+    (math.max(0, compactionBatchId - compactInterval)) until compactionBatchId
+  }
+
+  /**
+   * Returns all necessary logs before `batchId` (inclusive). If `batchId` is a compaction, just
+   * return itself. Otherwise, it will find the previous compaction batch and return all batches
+   * between it and `batchId`.
+   */
+  def getAllValidBatches(batchId: Long, compactInterval: Long): Seq[Long] = {
+    assert(batchId >= 0)
+    val start = math.max(0, (batchId + 1) / compactInterval * compactInterval - 1)
+    start to batchId
+  }
+
+  /**
+   * Returns the next compaction batch id after `batchId`.
+   */
+  def nextCompactionBatchId(batchId: Long, compactInterval: Long): Long = {
+    (batchId + compactInterval + 1) / compactInterval * compactInterval - 1
+  }
+}

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSink.scala

@@ -56,7 +56,8 @@ class FileStreamSink(
 
   private val basePath = new Path(path)
   private val logPath = new Path(basePath, FileStreamSink.metadataDir)
-  private val fileLog = new FileStreamSinkLog(sparkSession, logPath.toUri.toString)
+  private val fileLog =
+    new FileStreamSinkLog(FileStreamSinkLog.VERSION, sparkSession, logPath.toUri.toString)
   private val hadoopConf = sparkSession.sessionState.newHadoopConf()
   private val fs = basePath.getFileSystem(hadoopConf)