[GitHub] [arrow] jorgecarleitao commented on a change in pull request #9235: ARROW-11291: [Rust] Add extend to MutableBuffer (-25% for aritmetic, -97% for length)

[GitBox <gi...@apache.org>]

jorgecarleitao commented on a change in pull request #9235:
URL: https://github.com/apache/arrow/pull/9235#discussion_r559224772



##########
File path: rust/arrow/src/compute/kernels/length.rs
##########
@@ -30,16 +29,16 @@ where
     OffsetSize: OffsetSizeTrait,
 {
     // note: offsets are stored as u8, but they can be interpreted as OffsetSize
-    let offsets = array.data_ref().clone().buffers()[0].clone();
+    let offsets = &array.data_ref().buffers()[0];
     // this is a 30% improvement over iterating over u8s and building OffsetSize, which
     // justifies the usage of `unsafe`.
     let slice: &[OffsetSize] =
         &unsafe { offsets.typed_data::<OffsetSize>() }[array.offset()..];
 
-    let lengths: Vec<OffsetSize> = slice
-        .windows(2)
-        .map(|offset| offset[1] - offset[0])
-        .collect();
+    let lengths = slice.windows(2).map(|offset| offset[1] - offset[0]);
+
+    let mut buffer = MutableBuffer::new(0);
+    buffer.extend_from_exact_iter(lengths);
 

Review comment:
       This is the main difference in this PR for the length: we extend from the iterator instead of extending a vector and then memcopying the data.




----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org