[GitHub] [spark] viirya commented on a change in pull request #32272: [SPARK-35172][SS] The implementation of RocksDBCheckpointMetadata

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viirya commented on a change in pull request #32272:
URL: https://github.com/apache/spark/pull/32272#discussion_r618074831



##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/RocksDBFileManager.scala
##########
@@ -0,0 +1,165 @@
+/*
+ * 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.state
+
+import java.io.File
+import java.nio.charset.StandardCharsets.UTF_8
+import java.nio.file.Files
+
+import scala.collection.Seq
+
+import com.fasterxml.jackson.annotation.JsonInclude.Include
+import com.fasterxml.jackson.databind.{DeserializationFeature, ObjectMapper}
+import com.fasterxml.jackson.module.scala.{DefaultScalaModule, ScalaObjectMapper}
+import org.json4s.NoTypeHints
+import org.json4s.jackson.Serialization
+
+/**
+ * Classes to represent metadata of checkpoints saved to DFS. Since this is converted to JSON, any
+ * changes to this MUST be backward-compatible.
+ */
+case class RocksDBCheckpointMetadata(
+    sstFiles: Seq[RocksDBSstFile],
+    logFiles: Seq[RocksDBLogFile],
+    numKeys: Long) {
+  import RocksDBCheckpointMetadata._
+
+  def json: String = {
+    // We turn this field into a null to avoid write a empty logFiles field in the json.
+    val nullified = if (logFiles.isEmpty) this.copy(logFiles = null) else this

Review comment:
       why we need to avoid it?




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