Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/2792#discussion_r88861382
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/runtime/aggregate/IncrementalAggregateReduceFunction.scala
---
@@ -0,0 +1,69 @@
+/*
+ * 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.flink.api.table.runtime.aggregate
+
+import org.apache.flink.api.common.functions.ReduceFunction
+import org.apache.flink.api.table.Row
+import org.apache.flink.util.Preconditions
+
+/**
+ * For Incremental intermediate aggregate Rows, merge every row into
aggregate buffer.
+ *
+ * @param aggregates The aggregate functions.
+ * @param groupKeysMapping The index mapping of group keys between
intermediate aggregate Row
+ * and output Row.
+ */
+class IncrementalAggregateReduceFunction(
+ private val aggregates: Array[Aggregate[_]],
+ private val groupKeysMapping: Array[(Int, Int)],
+ private val intermediateRowArity: Int)extends ReduceFunction[Row] {
+
+ Preconditions.checkNotNull(aggregates)
+ Preconditions.checkNotNull(groupKeysMapping)
+ @transient var accumulatorRow:Row = _
+
+ /**
+ * For Incremental intermediate aggregate Rows, merge value1 and value2
+ * into aggregate buffer, return aggregate buffer.
+ *
+ * @param value1 The first value to combined.
+ * @param value2 The second value to combined.
+ * @return The combined value of both input values.
+ *
+ */
+ override def reduce(value1: Row, value2: Row): Row = {
+
+ if(null == accumulatorRow){
+ accumulatorRow = new Row(intermediateRowArity)
+ }
+
+ // Initiate intermediate aggregate value.
+ aggregates.foreach(_.initiate(accumulatorRow))
--- End diff --
I think a lot of people would use it for production use cases. (Maybe
you're confusing this with the old distinction between `MemStateBackend` and
`FsStateBackend`? Internally, both memory and file backend now use a
`HeapStateBackend` but for the file backend the contents are checkpointed to a
FileSystem.)
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