Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/10435#discussion_r48646183
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/misc.scala
---
@@ -177,3 +179,44 @@ case class Crc32(child: Expression) extends
UnaryExpression with ImplicitCastInp
})
}
}
+
+/**
+ * A function that calculates hash value for a group of expressions.
+ *
+ * Internally this function will write arguments into an [[UnsafeRow]],
and calculate hash code of
+ * the unsafe row using murmur3 hasher with a seed.
+ * We should use this hash function for both shuffle and bucket, so that
we can guarantee shuffle
+ * and bucketing have same data distribution.
+ */
+case class Murmur3Hash(children: Seq[Expression], seed: Int) extends
Expression {
+ def this(arguments: Seq[Expression]) = this(arguments, 42)
--- End diff --
use 42 as default seed, which is same with `UnsafeRow.hashCode`, should we
make `42` a constant variable in `Murmur3_x86_32`?
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