[GitHub] [iceberg] abmo-x commented on a diff in pull request #7363: Spark 3.2: Optimized add_files procedure's listPartitions

["abmo-x (via GitHub)" <gi...@apache.org>]

abmo-x commented on code in PR #7363:
URL: https://github.com/apache/iceberg/pull/7363#discussion_r1189039431


##########
spark/v3.2/spark/src/main/scala/org/apache/spark/sql/execution/datasources/InMemoryPartitionPathsIndex.scala:
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@@ -0,0 +1,122 @@
+/*
+ * 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.datasources
+import org.apache.hadoop.fs._
+import org.apache.spark.sql.SparkSession
+import org.apache.spark.sql.types.StructType
+import scala.collection.mutable
+
+
+/**
+ * Implement our own in-memory index which will only list directories to avoid unnecessary file
+ * listings. Should ONLY be used to get partition directory paths. Uses table's schema to only
+ * visit partition dirs using number of partition columns depth recursively. Does NOT return files
+ * within leaf dir.
+ */
+class InMemoryPartitionPathsIndex(
+                         sparkSession: SparkSession,
+                         rootPath :Path,
+                         parameters: Map[String, String],
+                         userSpecifiedSchema: StructType,
+                         fileStatusCache: FileStatusCache = NoopCache,
+                         override val metadataOpsTimeNs: Option[Long] = None)
+  extends PartitioningAwareFileIndex(
+    sparkSession, parameters, Some(userSpecifiedSchema), fileStatusCache) {
+
+  override val rootPaths = Seq(rootPath)
+
+  @volatile private var cachedLeafFiles: mutable.LinkedHashMap[Path, FileStatus] = _
+  @volatile private var cachedLeafDirToChildrenFiles: Map[Path, Array[FileStatus]] = _
+  @volatile private var cachedPartitionSpec: PartitionSpec = _
+
+  refresh0()
+
+  override def partitionSpec(): PartitionSpec = {
+    if (cachedPartitionSpec == null) {
+        cachedPartitionSpec = inferPartitioning()
+    }
+    logTrace(s"Partition spec: $cachedPartitionSpec")
+    cachedPartitionSpec
+  }
+
+  override def allFiles(): Seq[FileStatus] = cachedLeafFiles.values.toSeq
+
+  override protected def leafFiles: mutable.LinkedHashMap[Path, FileStatus] = cachedLeafFiles
+
+  override protected def leafDirToChildrenFiles: Map[Path, Array[FileStatus]] = cachedLeafDirToChildrenFiles
+
+  override def refresh(): Unit = {
+    fileStatusCache.invalidateAll()
+    refresh0()
+  }
+
+  private def refresh0(): Unit = {
+    val files = listLeafDirs(rootPath, 0)
+    cachedLeafFiles =
+      new mutable.LinkedHashMap[Path, FileStatus]() ++= files.map(f => f.getPath -> f)
+    cachedLeafDirToChildrenFiles = files.map( f => (f.getPath, Array(createEmptyChildDataFileStatus(f))))
+      .toMap
+    cachedPartitionSpec = null
+  }
+
+  override def equals(other: Any): Boolean = other match {
+    case hdfs: InMemoryFileIndex => rootPaths.toSet == hdfs.rootPaths.toSet
+    case _ => false
+  }
+
+  override def hashCode(): Int = rootPaths.toSet.hashCode()
+
+  /**
+   * recursively lists only the partition dirs. Uses the number of partition cols

Review Comment:
   @szehon-ho 
   correct, original method may distribute the task to list files.
   
   However, in our implementation as we **don't** list files and _only_ list directories, we don't need parallelism as listing  just dirs will be quicker or not that many compared to listing files in each dir.



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