Github user sameeragarwal commented on a diff in the pull request:
https://github.com/apache/spark/pull/14174#discussion_r71924045
--- Diff:
sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/RowBasedKeyValueBatch.java
---
@@ -0,0 +1,182 @@
+/*
+ * 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.catalyst.expressions;
+
+import java.io.IOException;
+
+import org.apache.spark.memory.MemoryConsumer;
+import org.apache.spark.memory.TaskMemoryManager;
+import org.apache.spark.sql.types.*;
+import org.apache.spark.unsafe.memory.MemoryBlock;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * RowBasedKeyValueBatch stores key value pairs in contiguous memory
region.
+ *
+ * Each key or value is stored as a single UnsafeRow. Each record contains
one key and one value
+ * and some auxiliary data, which differs based on implementation:
+ * i.e., `FixedLengthRowBasedKeyValueBatch` and
`VariableLengthRowBasedKeyValueBatch`.
+ *
+ * We use `FixedLengthRowBasedKeyValueBatch` if all fiends in the key and
the value are fixed-length
+ * data types. Otherwise we use `VariableLengthRowBasedKeyValueBatch`.
+ *
+ * RowBasedKeyValueBatch is backed by a single page / MemoryBlock
(defaults to 64MB). If the page
+ * is full, the aggregate logic should fallback to a second level, larger
hash map. We intentionally
+ * use the single-page design because it simplifies memory address
encoding & decoding for each
+ * key-value pair. Because the maximum capacity for RowBasedKeyValueBatch
is only 2^16, it is
+ * unlikely we need a second page anyway. Filling the page requires an
average size for key value
+ * pairs to be larger than 1024 bytes.
+ *
+ */
+public abstract class RowBasedKeyValueBatch extends MemoryConsumer {
+ protected final Logger logger =
LoggerFactory.getLogger(RowBasedKeyValueBatch.class);
+
+ protected static final int DEFAULT_CAPACITY = 1 << 16;
--- End diff --
This and `DEFAULT_PAGE_SIZE` can probably be private?
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