[GitHub] [arrow] Dandandan commented on a change in pull request #8485: ARROW-10002: [Rust] Remove trait specialization from arrow crate

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Dandandan commented on a change in pull request #8485:
URL: https://github.com/apache/arrow/pull/8485#discussion_r535140816



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File path: rust/arrow/src/array/builder.rs
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@@ -253,8 +253,18 @@ pub trait BufferBuilderTrait<T: ArrowPrimitiveType> {
 }
 
 impl<T: ArrowPrimitiveType> BufferBuilderTrait<T> for BufferBuilder<T> {
-    default fn new(capacity: usize) -> Self {
-        let buffer = MutableBuffer::new(capacity * mem::size_of::<T::Native>());
+    #[inline]
+    fn new(capacity: usize) -> Self {
+        let buffer = if T::DATA_TYPE == DataType::Boolean {

Review comment:
       @jorgecarleitao 
   
   I see this in profiling for BufferBuilderTrait append:
   
   ![image](https://user-images.githubusercontent.com/163737/101012554-4c1dfc00-3563-11eb-9b00-f92eac06b7ae.png)
   
   Which accounts for 9% of the instruction fetches according to callgrind when running the TPHC 12 benchmark.
   
   So it seems the `if T::DATA_TYPE == DataType::Boolean` is not being optimized out and goes into the partial eq implementation (or the profiler is wrong), maybe because the implementation there is not easy to optimize / specialize for this case. I will check if another implementation (pattern match?) solves this.




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