Re: [PR] [SS][SPARK-46816] Add base support for new arbitrary state management operator, single valueState type, multiple state variables and underlying support for column families for RocksDBStateStoreProvider with/without changelog checkpointing [spark]

["anishshri-db (via GitHub)" <gi...@apache.org>]

anishshri-db commented on code in PR #43961:
URL: https://github.com/apache/spark/pull/43961#discussion_r1463844823


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sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/ValueStateImpl.scala:
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@@ -0,0 +1,109 @@
+/*
+ * 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.Serializable
+
+import org.apache.commons.lang3.SerializationUtils
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.execution.streaming.state.StateStore
+import org.apache.spark.sql.streaming.ValueState
+import org.apache.spark.sql.types._
+
+/**
+ * Class that provides a concrete implementation for a single value state associated with state
+ * variables used in the streaming transformWithState operator.
+ * @param store - reference to the StateStore instance to be used for storing state
+ * @param stateName - name of logical state partition
+ * @tparam S - data type of object that will be stored
+ */
+class ValueStateImpl[S](
+    store: StateStore,
+    stateName: String) extends ValueState[S] with Logging {
+
+  // TODO: validate places that are trying to encode the key and check if we can eliminate/
+  // add caching for some of these calls.
+  private def encodeKey(): UnsafeRow = {
+    val keyOption = ImplicitKeyTracker.getImplicitKeyOption
+    if (!keyOption.isDefined) {
+      throw new UnsupportedOperationException("Implicit key not found for operation on" +
+        s"stateName=$stateName")
+    }
+
+    val schemaForKeyRow: StructType = new StructType().add("key", BinaryType)
+    val keyByteArr = SerializationUtils.serialize(keyOption.get.asInstanceOf[Serializable])
+    val keyEncoder = UnsafeProjection.create(schemaForKeyRow)
+    val keyRow = keyEncoder(InternalRow(keyByteArr))
+    keyRow
+  }
+
+  private def encodeValue(value: S): UnsafeRow = {
+    val schemaForValueRow: StructType = new StructType().add("value", BinaryType)
+    val valueByteArr = SerializationUtils.serialize(value.asInstanceOf[Serializable])
+    val valueEncoder = UnsafeProjection.create(schemaForValueRow)
+    val valueRow = valueEncoder(InternalRow(valueByteArr))
+    valueRow
+  }
+
+  /** Function to check if state exists. Returns true if present and false otherwise */
+  override def exists(): Boolean = {
+    getImpl() != null
+  }
+
+  /** Function to return Option of value if exists and None otherwise */
+  override def getOption(): Option[S] = {
+    val retRow = getImpl()
+    if (retRow != null) {
+      val resState = SerializationUtils
+        .deserialize(retRow.getBinary(0))
+        .asInstanceOf[S]
+      Some(resState)
+    } else {
+      None
+    }
+  }
+
+  /** Function to return associated value with key if exists and null otherwise */
+  override def get(): S = {

Review Comment:
   Not really. Most APIs for get queries would return null. The expectation is for users to check if the key exists first. But if it doesn't - then users can still filter on null being returned. 
   
   Similar approach for RocksDB - https://javadoc.io/doc/org.rocksdb/rocksdbjni/6.8.1/org/rocksdb/RocksDB.html#get(byte[])



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