Dandandan commented on a change in pull request #9016:
URL: https://github.com/apache/arrow/pull/9016#discussion_r549110164



##########
File path: rust/arrow/src/array/array_string.rs
##########
@@ -126,25 +126,28 @@ impl<OffsetSize: StringOffsetSizeTrait> 
GenericStringArray<OffsetSize> {
     }
 
     pub(crate) fn from_vec(v: Vec<&str>) -> Self {
-        let mut offsets = Vec::with_capacity(v.len() + 1);
-        let mut values = Vec::new();
+        let mut offsets =
+            MutableBuffer::new((v.len() + 1) * 
std::mem::size_of::<OffsetSize>());
+        let mut values = MutableBuffer::new(0);

Review comment:
       Probably the offset buffer is also faster after converting it to 
`typed_data_mut::<OffsetSize>` and iterating it with `iter_mut`, this way it 
can skip the capacity checks, and also current conversion to a byte slice may 
add some overhead?




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