Github user sameeragarwal commented on a diff in the pull request:
https://github.com/apache/spark/pull/14174#discussion_r71254476
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/RowBasedHashMapGenerator.scala
---
@@ -0,0 +1,338 @@
+/*
+ * 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.aggregate
+
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import
org.apache.spark.sql.catalyst.expressions.aggregate.{AggregateExpression,
DeclarativeAggregate}
+import org.apache.spark.sql.catalyst.expressions.codegen.{CodegenContext,
ExprCode}
+import org.apache.spark.sql.types._
+
+/**
+ * This is a helper class to generate an append-only row-based hash map
that can act as a 'cache'
+ * for extremely fast key-value lookups while evaluating aggregates (and
fall back to the
+ * `BytesToBytesMap` if a given key isn't found). This is 'codegened' in
HashAggregate to speed
+ * up aggregates w/ key.
+ *
+ * We also have VectorizedHashMapGenerator, which generates a append-only
vectorized hash map.
+ * We choose one of the two as the 1st level, fast hash map during
aggregation.
+ *
+ * NOTE: This row-based hash map currently doesn't support nullable keys
and falls back to the
+ * `BytesToBytesMap` to store them.
+ */
+class RowBasedHashMapGenerator(
--- End diff --
One thing that might be nice to do (perhaps as part of a small followup PR)
is to reduce the code duplication between this and the
`VectorizedHashMapGenerator` by having these 2 just extend a base class
`HashMapGenerator`.
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