[GitHub] [spark] viirya commented on a change in pull request #26935: [SPARK-30294][SS] Explicitly defines read-only StateStore and optimize for HDFSBackedStateStore

[GitBox <gi...@apache.org>]

viirya commented on a change in pull request #26935:
URL: https://github.com/apache/spark/pull/26935#discussion_r498629306



##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateStoreRDD.scala
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@@ -29,6 +29,57 @@ import org.apache.spark.sql.internal.SessionState
 import org.apache.spark.sql.types.StructType
 import org.apache.spark.util.SerializableConfiguration
 
+/**
+ * An RDD that allows computations to be executed against [[ReadOnlyStateStore]]s. It
+ * uses the [[StateStoreCoordinator]] to get the locations of loaded state stores
+ * and use that as the preferred locations.
+ */
+class ReadOnlyStateStoreRDD[T: ClassTag, U: ClassTag](
+    dataRDD: RDD[T],
+    storeReadFunction: (ReadOnlyStateStore, Iterator[T]) => Iterator[U],
+    checkpointLocation: String,
+    queryRunId: UUID,
+    operatorId: Long,
+    storeVersion: Long,
+    keySchema: StructType,
+    valueSchema: StructType,
+    indexOrdinal: Option[Int],
+    sessionState: SessionState,
+    @transient private val storeCoordinator: Option[StateStoreCoordinatorRef],
+    extraOptions: Map[String, String] = Map.empty) extends RDD[U](dataRDD) {
+
+  private val storeConf = new StateStoreConf(sessionState.conf, extraOptions)
+
+  // A Hadoop Configuration can be about 10 KB, which is pretty big, so broadcast it
+  private val hadoopConfBroadcast = dataRDD.context.broadcast(
+    new SerializableConfiguration(sessionState.newHadoopConf()))
+
+  override protected def getPartitions: Array[Partition] = dataRDD.partitions
+
+  /**
+   * Set the preferred location of each partition using the executor that has the related
+   * [[StateStoreProvider]] already loaded.
+   */
+  override def getPreferredLocations(partition: Partition): Seq[String] = {
+    val stateStoreProviderId = StateStoreProviderId(
+      StateStoreId(checkpointLocation, operatorId, partition.index),
+      queryRunId)
+    storeCoordinator.flatMap(_.getLocation(stateStoreProviderId)).toSeq
+  }
+
+  override def compute(partition: Partition, ctxt: TaskContext): Iterator[U] = {
+    val storeProviderId = StateStoreProviderId(
+      StateStoreId(checkpointLocation, operatorId, partition.index),
+      queryRunId)
+
+    val store = StateStore.getReadOnly(
+      storeProviderId, keySchema, valueSchema, indexOrdinal, storeVersion,

Review comment:
       Sounds too complicated, and it's also a bit weird and read-only store calls both abort and close. Let's keep with original abort and commit for now.




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