Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/13680#discussion_r68538811
--- Diff:
sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/UnsafeArrayData.java
---
@@ -25,17 +25,21 @@
import org.apache.spark.sql.types.*;
import org.apache.spark.unsafe.Platform;
import org.apache.spark.unsafe.array.ByteArrayMethods;
+import org.apache.spark.unsafe.bitset.BitSetMethods;
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 three parts: [numElements] [offsets] [values]
+ * Each tuple has three four: [numElements] [null bits] [values] [variable
length portion]
*
* The `numElements` is 4 bytes storing the number of elements of this
array.
*
+ * In the `null bits` region, we store 1 bit per element, represents
whether a element has null
+ * Its total size is ceil(numElements / 8) bytes, and it is aligned to
8-byte word boundaries.
+ *
* In the `offsets` region, we store 4 bytes per element, represents the
relative offset (w.r.t. the
--- End diff --
we should update this, it's not `offset` region anymore
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