Github user zsxwing commented on a diff in the pull request:
https://github.com/apache/spark/pull/12435#discussion_r60279243
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSinkLog.scala
---
@@ -0,0 +1,255 @@
+/*
+ * 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
+
+/**
+ * The status of a file outputted by [[FileStreamSink]]. A file is visible
only if it appears in
+ * the sink log and its action is not "delete".
+ *
+ * @param path the file path
+ * @param size the file size
+ * @param action the file action. Must be either "add" or "delete".
+ */
+case class SinkFileStatus(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 [[SinkFileStatus]].
+ *
+ * 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
+ * compaction, it will read all old log files and merge them with the new
batch. During the
+ * compaction, it will also delete the files that are deleted (marked by
[[SinkFileStatus.action]]).
+ * When the reader uses `allFiles` to list all files, this method only
returns the visible files
+ * (drops the deleted files).
+ */
+class FileStreamSinkLog(sqlContext: SQLContext, path: String)
+ extends HDFSMetadataLog[Seq[SinkFileStatus]](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 `fileCleanupDelayMs`. We will wait until then
so that the compaction
+ * file is guaranteed to be visible for all readers
+ */
+ private val fileCleanupDelayMs =
sqlContext.getConf(SQLConf.FILE_SINK_LOG_CLEANUP_DELAY)
--- End diff --
@steveloughran thanks for pointing out it. I updated the codes. Now it will
try to access the next compaction/aggregate file directly. However, a cleanup
delay is still helpful to avoid a live lock.
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