[GitHub] [arrow-rs] tustvold commented on a diff in pull request #3695: feat: Sort kernel for `RunArray`

["tustvold (via GitHub)" <gi...@apache.org>]

tustvold commented on code in PR #3695:
URL: https://github.com/apache/arrow-rs/pull/3695#discussion_r1106244242


##########
arrow-array/src/run_iterator.rs:
##########
@@ -57,13 +57,8 @@ where
 {
     /// create a new iterator
     pub fn new(array: TypedRunArray<'a, R, V>) -> Self {
-        let current_front_physical: usize =
-            array.run_array().get_physical_index(0).unwrap();
-        let current_back_physical: usize = array
-            .run_array()
-            .get_physical_index(array.len() - 1)
-            .unwrap()
-            + 1;
+        let current_front_physical: usize = array.run_array().get_start_physical_index();
+        let current_back_physical: usize = array.run_array().get_end_physical_index() + 1;

Review Comment:
   ```suggestion
           let current_front_physical = array.run_array().get_start_physical_index();
           let current_back_physical = array.run_array().get_end_physical_index() + 1;
   ```



##########
arrow-ord/src/sort.rs:
##########
@@ -599,6 +618,206 @@ fn insert_valid_values<T>(result_slice: &mut [u32], offset: usize, valids: &[(u3
     append_valids(&mut result_slice[offset..offset + valids.len()]);
 }
 
+// Sort run array and return sorted run array.
+// The output RunArray will be encoded at the same level as input run array.
+// For e.g. an input RunArray { run_ends = [2,4,6,8], values = [1,2,1,2] }
+// will result in output RunArray { run_ends = [2,4,6,8], values = [1,1,2,2] }
+// and not RunArray { run_ends = [4,8], values = [1,2] }
+fn sort_run(

Review Comment:
   How much of a performance difference does this special case have? At least for query engines, it is very rare to be sorting a single column by itself, more common is sorting multiple columns by one (i.e. sort_to_indices) or more (i.e. lexsort_to_indices) other columns? 



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