Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/7752#discussion_r36039963
--- Diff:
sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/UnsafeArrayData.java
---
@@ -0,0 +1,354 @@
+/*
+ * 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.math.BigDecimal;
+import java.math.BigInteger;
+
+import org.apache.spark.sql.catalyst.InternalRow;
+import org.apache.spark.sql.types.*;
+import org.apache.spark.unsafe.PlatformDependent;
+import org.apache.spark.unsafe.array.ByteArrayMethods;
+import org.apache.spark.unsafe.hash.Murmur3_x86_32;
+import org.apache.spark.unsafe.types.CalendarInterval;
+import org.apache.spark.unsafe.types.UTF8String;
+
+/**
+ * An Unsafe implementation of Array which is backed by raw memory instead
of Java objects.
+ *
+ * Each tuple has two parts: [offsets] [values]
+ *
+ * In the `offsets` region, we store 4 bytes per element, represents the
start address of this
+ * element in `values` region. We can get the length of this element by
subtracting next offset.
+ * Note that offset can by negative which means this element is null.
+ *
+ * In ghe `values` region, we store the content of elements. As we can get
length info, so elements
+ * can be variable-length.
+ *
+ * Note that when we write out this array, we should write out the
`numElements` at first 4 bytes,
+ * then follows content. When we read in an array, we should read first 4
bytes as `numElements`
+ * and take the rest as content.
+ *
+ * Instances of `UnsafeArrayData` act as pointers to row data stored in
this format.
+ */
+// todo: there is a lof of duplicated code between UnsafeRow and
UnsafeArrayData.
--- End diff --
He's already done with it hasn't he?
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