Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/21662#discussion_r199286349
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamingLimitExec.scala
---
@@ -0,0 +1,96 @@
+/*
+ * 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.util.concurrent.TimeUnit.NANOSECONDS
+
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.Attribute
+import org.apache.spark.sql.catalyst.expressions.GenericInternalRow
+import org.apache.spark.sql.catalyst.expressions.UnsafeProjection
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import org.apache.spark.sql.catalyst.plans.physical.{AllTuples,
Distribution, Partitioning}
+import org.apache.spark.sql.execution.{SparkPlan, UnaryExecNode}
+import org.apache.spark.sql.execution.streaming.state.StateStoreOps
+import org.apache.spark.sql.types.{LongType, NullType, StructField,
StructType}
+import org.apache.spark.util.CompletionIterator
+
+/**
+ * A physical operator for executing a streaming limit, which makes sure
no more than streamLimit
+ * rows are returned.
+ */
+case class StreamingLimitExec(
+ streamLimit: Long,
+ child: SparkPlan,
+ stateInfo: Option[StatefulOperatorStateInfo] = None)
+ extends UnaryExecNode with StateStoreWriter {
+
+ private val keySchema = StructType(Array(StructField("key", NullType)))
+ private val valueSchema = StructType(Array(StructField("value",
LongType)))
+
+ override protected def doExecute(): RDD[InternalRow] = {
+ metrics // force lazy init at driver
+
+ child.execute().mapPartitionsWithStateStore(
+ getStateInfo,
+ keySchema,
+ valueSchema,
+ indexOrdinal = None,
+ sqlContext.sessionState,
+ Some(sqlContext.streams.stateStoreCoordinator)) { (store, iter) =>
+ val key = UnsafeProjection.create(keySchema)(new
GenericInternalRow(Array[Any](null)))
+ val numOutputRows = longMetric("numOutputRows")
+ val numUpdatedStateRows = longMetric("numUpdatedStateRows")
+ val allUpdatesTimeMs = longMetric("allUpdatesTimeMs")
+ val commitTimeMs = longMetric("commitTimeMs")
+ val updatesStartTimeNs = System.nanoTime
+
+ val startCount: Long =
Option(store.get(key)).map(_.getLong(0)).getOrElse(0L)
+ var rowCount = startCount
+
+ val result = iter.filter { r =>
+ val x = rowCount < streamLimit
--- End diff --
I think its okay due to `override def requiredChildDistribution:
Seq[Distribution] = AllTuples :: Nil`.
+1 to making sure there are tests with more than one partition though.
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