Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/13680#discussion_r79559429
--- Diff:
sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/UnsafeArrayData.java
---
@@ -25,55 +25,58 @@
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 array has four parts:
+ * [numElements][null bits][values or offset&length][variable length
portion]
*
- * The `numElements` is 4 bytes storing the number of elements of this
array.
+ * The `numElements` is 8 bytes storing the number of elements of this
array.
*
- * In the `offsets` region, we store 4 bytes per element, represents the
relative offset (w.r.t. the
- * base address of the array) 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 the `null bits` region, we store 1 bit per element, represents
whether a element has null
--- End diff --
`an element is null`
---
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