Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/12435#discussion_r60133882
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSinkLog.scala
---
@@ -0,0 +1,241 @@
+/*
+ * 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 org.apache.hadoop.fs.{Path, PathFilter}
+import org.json4s.NoTypeHints
+import org.json4s.jackson.Serialization
+import org.json4s.jackson.Serialization.{read, write}
+
+import org.apache.spark.sql.SQLContext
+import org.apache.spark.sql.internal.SQLConf
+
+/**
+ * @param path the file path
+ * @param size the file size
+ * @param action the file action. Must be either "add" or "delete".
+ */
+case class FileLog(path: String, size: Long, action: String)
+
+/**
+ * A special log for [[FileStreamSink]]. It will write one log file for
each batch. The first line
+ * of the log file is the version number, and there are multiple JSON
lines following. Each JSON
+ * line is a JSON format of [[FileLog]].
+ *
+ * As reading from many small files is usually pretty slow,
[[FileStreamSinkLog]] will compact log
+ * files every "spark.sql.sink.file.log.compactLen" batches into a big
file. When doing a compact,
+ * it will read all history logs and merge them with the new batch. During
the compaction, it will
+ * also delete the files that are deleted (marked by [[FileLog.action]]).
When the reader uses
+ * `allLogs` to list all files, this method only returns the visible files
(drops the deleted
+ * files).
+ */
+class FileStreamSinkLog(sqlContext: SQLContext, path: String)
+ extends HDFSMetadataLog[Seq[FileLog]](sqlContext, path) {
+
+ import FileStreamSinkLog._
+
+ private implicit val formats = Serialization.formats(NoTypeHints)
+
+ /**
+ * 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. The user
+ * should set a reasonable `fileExpiredTimeMS`. We will wait until then
so that the compaction
+ * file is guaranteed to be visible for all readers
+ */
+ private val fileExpiredTimeMS =
sqlContext.getConf(SQLConf.FILE_STREAM_SINK_LOG_EXPIRED_TIME)
+
+ private val isDeletingExpiredLog =
sqlContext.getConf(SQLConf.FILE_STREAM_SINK_LOG_DELETE)
+
+ private val compactLength =
sqlContext.getConf(SQLConf.FILE_STREAM_SINK_LOG_COMPACT_LEN)
+
+ override def batchIdToPath(batchId: Long): Path = {
+ if (isCompactionBatch(batchId, compactLength)) {
+ 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(logs: Seq[FileLog]): Array[Byte] = {
+ (VERSION +: logs.map(write(_))).mkString("\n").getBytes(UTF_8)
+ }
+
+ override def deserialize(bytes: Array[Byte]): Seq[FileLog] = {
+ 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 != VERSION) {
+ throw new IllegalStateException(s"Unknown log version: ${version}")
+ }
+ lines.toSeq.slice(1, lines.length).map(read[FileLog](_))
+ }
+
+ override def add(batchId: Long, logs: Seq[FileLog]): Boolean = {
+ if (isCompactionBatch(batchId, compactLength)) {
+ 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.
+ */
+ private def compact(batchId: Long, logs: Seq[FileLog]): Boolean = {
+ val validBatches = getValidBatchesBeforeCompactionBatch(batchId,
compactLength)
+ val allLogs = validBatches.flatMap(batchId => get(batchId)).flatten ++
logs
+ if (super.add(batchId, compactLogs(allLogs))) {
+ if (isDeletingExpiredLog) {
+ deleteExpiredLog(batchId)
+ }
+ true
+ } else {
+ // Return false as there is another writer.
+ false
+ }
+ }
+
+ /**
+ * Returns all file logs except the deleted files.
+ */
+ def allLogs(): Array[FileLog] = {
--- End diff --
nit: Can you move the public method higher up over the private methods?
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