HyukjinKwon commented on a change in pull request #25602: [SPARK-28613][SQL] 
Add config option for limiting uncompressed result size in SQL
URL: https://github.com/apache/spark/pull/25602#discussion_r321570821
 
 

 ##########
 File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/SizeLimitingByteArrayDecoder.scala
 ##########
 @@ -0,0 +1,80 @@
+/*
+ * 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
+
+import java.io.{ByteArrayInputStream, DataInputStream}
+
+import org.apache.spark.{SparkEnv, SparkException}
+import org.apache.spark.internal.{config, Logging}
+import org.apache.spark.io.CompressionCodec
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.util.Utils
+
+/**
+ * Provides methods for converting compressed byte arrays back to UnsafeRows.
+ * Additionally, can enforce a limit on the total, decoded size of all decoded 
UnsafeRows.
+ * Enforcing the limit is controlled via a sql config and if it is turned on 
the encoder will
+ * throw a SparkException when the limit is reached.
+ */
+private[spark] class SizeLimitingByteArrayDecoder(
+     nFields: Int,
+     sqlConf: SQLConf) extends Logging {
+  private var totalUncompressedResultSize = 0L
+  private val maxUncompressedResultSize = sqlConf.maxUncompressedResultSize
+
+  /**
+   * Decodes the byte arrays back to UnsafeRows and puts them into buffer.
+   */
+  def decodeUnsafeRows(bytes: Array[Byte]): Iterator[InternalRow] = {
+    val codec = CompressionCodec.createCodec(SparkEnv.get.conf)
+    val bis = new ByteArrayInputStream(bytes)
+    val ins = new DataInputStream(codec.compressedInputStream(bis))
+
+    new Iterator[InternalRow] {
+      private var sizeOfNextRow = ins.readInt()
+
+      override def hasNext: Boolean = sizeOfNextRow >= 0
+
+      override def next(): InternalRow = {
+        ensureCanFetchMoreResults(sizeOfNextRow)
+        val bs = new Array[Byte](sizeOfNextRow)
+        ins.readFully(bs)
+        val row = new UnsafeRow(nFields)
+        row.pointTo(bs, sizeOfNextRow)
+        sizeOfNextRow = ins.readInt()
+        row
+      }
+    }
+  }
+
+  private def ensureCanFetchMoreResults(sizeOfNextRow: Int): Unit = {
+    totalUncompressedResultSize += sizeOfNextRow
 
 Review comment:
   Yea, I don't think it's useful. I think there's no point here since it's 
already collected.

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