Github user tejasapatil commented on a diff in the pull request:
https://github.com/apache/spark/pull/16909#discussion_r101201086
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/ExternalAppendOnlyUnsafeRowArray.scala
---
@@ -0,0 +1,218 @@
+/*
+ * 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.util.ConcurrentModificationException
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.{SparkEnv, TaskContext}
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import
org.apache.spark.sql.execution.ExternalAppendOnlyUnsafeRowArray.DefaultInitialSizeOfInMemoryBuffer
+import org.apache.spark.util.collection.unsafe.sort.{UnsafeExternalSorter,
UnsafeSorterIterator}
+
+/**
+ * An append-only array for [[UnsafeRow]]s that spills content to disk
when there a predefined
+ * threshold of rows is reached.
+ *
+ * Setting spill threshold faces following trade-off:
+ *
+ * - If the spill threshold is too high, the in-memory array may occupy
more memory than is
+ * available, resulting in OOM.
+ * - If the spill threshold is too low, we spill frequently and incur
unnecessary disk writes.
+ * This may lead to a performance regression compared to the normal case
of using an
+ * [[ArrayBuffer]] or [[Array]].
+ */
+private[sql] class ExternalAppendOnlyUnsafeRowArray(numRowsSpillThreshold:
Int) extends Logging {
+ private val initialSizeOfInMemoryBuffer =
+ Math.min(DefaultInitialSizeOfInMemoryBuffer, numRowsSpillThreshold)
+
+ private val inMemoryBuffer = new
ArrayBuffer[UnsafeRow](initialSizeOfInMemoryBuffer)
+
+ private var spillableArray: UnsafeExternalSorter = _
+ private var numRows = 0
+
+ // A counter to keep track of total modifications done to this array
since its creation.
+ // This helps to invalidate iterators when there are changes done to the
backing array.
+ private var modificationsCount: Long = 0
+
+ private var numFieldsPerRow = 0
+
+ def length: Int = numRows
+
+ def isEmpty: Boolean = numRows == 0
+
+ /**
+ * Clears up resources (eg. memory) held by the backing storage
+ */
+ def clear(): Unit = {
+ if (spillableArray != null) {
+ // The last `spillableArray` of this task will be cleaned up via
task completion listener
+ // inside `UnsafeExternalSorter`
+ spillableArray.cleanupResources()
+ spillableArray = null
+ } else {
+ inMemoryBuffer.clear()
+ }
+ numFieldsPerRow = 0
+ numRows = 0
+ modificationsCount += 1
+ }
+
+ def add(unsafeRow: UnsafeRow): Unit = {
+ if (numRows < numRowsSpillThreshold) {
+ inMemoryBuffer += unsafeRow.copy()
+ } else {
+ if (spillableArray == null) {
+ logInfo(s"Reached spill threshold of $numRowsSpillThreshold rows,
switching to " +
+ s"${classOf[UnsafeExternalSorter].getName}")
+
+ // We will not sort the rows, so prefixComparator and
recordComparator are null
+ spillableArray = UnsafeExternalSorter.create(
+ TaskContext.get().taskMemoryManager(),
+ SparkEnv.get.blockManager,
+ SparkEnv.get.serializerManager,
+ TaskContext.get(),
+ null,
+ null,
+ if (numRowsSpillThreshold > 2) numRowsSpillThreshold / 2 else 1,
+ SparkEnv.get.memoryManager.pageSizeBytes,
+ numRowsSpillThreshold,
+ false)
+
+ inMemoryBuffer.foreach(existingUnsafeRow =>
+ spillableArray.insertRecord(
+ existingUnsafeRow.getBaseObject,
+ existingUnsafeRow.getBaseOffset,
+ existingUnsafeRow.getSizeInBytes,
+ 0,
+ false)
+ )
+ inMemoryBuffer.clear()
+ numFieldsPerRow = unsafeRow.numFields()
+ }
+
+ spillableArray.insertRecord(
+ unsafeRow.getBaseObject,
+ unsafeRow.getBaseOffset,
+ unsafeRow.getSizeInBytes,
+ 0,
+ false)
+ }
+
+ numRows += 1
+ modificationsCount += 1
+ }
+
+ /**
+ * Creates an [[Iterator]] for the current rows in the array starting
from a user provided index
+ *
+ * If there are subsequent [[add()]] or [[clear()]] calls made on this
array after creation of
+ * the iterator, then the iterator is invalidated thus saving clients
from thinking that they
+ * have read all the data while there were new rows added to this array.
+ */
+ def generateIterator(startIndex: Int): Iterator[UnsafeRow] = {
+ if (startIndex < 0 || (numRows > 0 && startIndex > numRows)) {
+ throw new ArrayIndexOutOfBoundsException(
+ "Invalid `startIndex` provided for generating iterator over the
array. " +
+ s"Total elements: $numRows, requested `startIndex`: $startIndex")
+ }
+
+ if (spillableArray == null) {
+ new InMemoryBufferIterator(startIndex)
+ } else {
+ new SpillableArrayIterator(spillableArray.getIterator,
numFieldsPerRow, startIndex)
+ }
+ }
+
+ def generateIterator(): Iterator[UnsafeRow] = generateIterator(0)
--- End diff --
self review : will change this to `generateIterator(startIndex = 0)`
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