Github user jlhitt commented on a diff in the pull request:
https://github.com/apache/spark/pull/14762#discussion_r78978059
--- Diff:
common/unsafe/src/main/java/org/apache/spark/unsafe/array/ByteArrayMethods.java
---
@@ -47,13 +47,20 @@ public static int roundNumberOfBytesToNearestWord(int
numBytes) {
public static boolean arrayEquals(
Object leftBase, long leftOffset, Object rightBase, long
rightOffset, final long length) {
int i = 0;
- while (i <= length - 8) {
- if (Platform.getLong(leftBase, leftOffset + i) !=
- Platform.getLong(rightBase, rightOffset + i)) {
- return false;
- }
- i += 8;
- }
+
+ // This attempts to speed up the memcmp type of operation, but there
is no way
+ // to guarantee that the offsets will be on a word boundary in order
to use
+ // Platform.getLong
--- End diff --
No. The only way it can be used with the 8 byte copy is if both leftOffset
and rightOffset either start on proper word boundries, or are off of boundries
by the same degree. In practice, this absolute alignment between left and
right offsets happens very rarely. So rarely that the performance impact of
checking for it every time negates any advantage you get from performing it.
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