[GitHub] [arrow] Dandandan commented on a change in pull request #9016: ARROW-11037: [Rust] Optimized creation of string array from iterator.

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

Dandandan commented on a change in pull request #9016:
URL: https://github.com/apache/arrow/pull/9016#discussion_r549109082



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File path: rust/arrow/src/array/array_string.rs
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@@ -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:
       Might be interesting to test here whether it is cheaper to calculate offsets + total size first for `values` buffer based on final `length_so_far` so that it doesn't require extra allocations.




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